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Summary
Ammonia, with the chemical formula NH3, is a gas recognized by its strong, sharp smell. It is found in small quantities in the air and in traces in natural water. It also exists in combined forms, such as ammonium chloride. Because ammonia dissolves very easily in water, it does not occur as a mineral in the earth. The characteristic smell near decaying organic matter or toilets is often due to ammonia, which is produced when bacteria break down urea present in urine.
In the laboratory, ammonia gas is commonly prepared by heating an ammonium salt, like ammonium chloride, with an alkali, such as calcium hydroxide (also known as slaked lime). The mixture is heated in a flask that is tilted downwards. This position prevents any water formed during the chemical reaction from flowing back onto the hot glass, which could cause it to break. The ammonia gas produced is then dried by passing it through a tower containing quicklime (calcium oxide). Other drying agents, like concentrated sulphuric acid, are not suitable because ammonia is a basic gas and would react with these acidic substances. Ammonia gas is collected by the downward displacement of air because it is lighter than air. It cannot be collected over water because it dissolves in water very readily.
Industrially, ammonia is manufactured by the Haber’s Process. This important process combines nitrogen gas (obtained from the air) and hydrogen gas (often sourced from natural gas) in a 1:3 ratio by volume. The chemical reaction is N₂ + 3H₂ ⇌ 2NH₃, and it releases heat. For this reaction to occur efficiently, specific conditions are maintained: a temperature of about 450-500°C, very high pressure (above 200 atmospheres), and a catalyst made of finely divided iron. A substance called a promoter, like molybdenum, is also used to enhance the efficiency of the iron catalyst. The ammonia formed is separated from unreacted nitrogen and hydrogen by cooling the mixture, which causes the ammonia to turn into a liquid. The unreacted gases are then recycled back into the process to produce more ammonia.
Ammonia is a colorless gas with a pungent smell and is significantly lighter than air. One of its most distinct physical properties is its very high solubility in water. The “fountain experiment” clearly demonstrates this: when a few drops of water are introduced into a flask filled with ammonia gas, the ammonia dissolves rapidly. This creates an area of low pressure inside the flask. As a result, red litmus solution from a container below is forced up through a tube into the flask, emerging as a blue fountain. This color change also shows that a solution of ammonia in water is alkaline, or basic.
While dry ammonia gas is neutral, when it dissolves in water, it forms ammonium hydroxide (NH₄OH), which is a weak base. Ammonia gas can burn in oxygen with a greenish-yellow flame, producing nitrogen gas and water vapor. If a catalyst like platinum is present and the temperature is high (around 800°C), ammonia reacts with oxygen to form nitric oxide. This is a key step in the industrial production of nitric acid. Ammonia also acts as a reducing agent. For example, it can remove oxygen from hot copper (II) oxide, changing the black colored oxide into reddish-brown copper metal, while the ammonia itself is converted into nitrogen and water. When ammonia reacts with chlorine gas, the products depend on which gas is in excess. If ammonia is in excess, nitrogen gas and white fumes of ammonium chloride are formed. However, if chlorine is in excess, an explosive yellow liquid called nitrogen trichloride is produced. Ammonia readily reacts with acids to form ammonium salts. For instance, with hydrochloric acid, it forms ammonium chloride. An aqueous solution of ammonia (ammonium hydroxide) reacts with solutions of many metal salts to form precipitates of metal hydroxides, which often have characteristic colors.
Ammonia gas can be identified by its distinctive sharp smell. It also turns moist red litmus paper blue. Another common test is to bring a glass rod dipped in concentrated hydrochloric acid near ammonia; if ammonia is present, dense white fumes of ammonium chloride will be observed.
Ammonia has numerous important uses. Liquid ammonia is used as a refrigerant in ice-making plants and refrigeration systems because it absorbs a large amount of heat when it evaporates, thus causing cooling. Aqueous ammonia is used as a cleaning agent to remove grease stains from clothes and to clean windows and tiles. Ammonia is very important in the manufacture of nitrogenous fertilizers, such as urea and ammonium sulphate, which are essential for plant growth. It is also used to make explosives like ammonium nitrate, in the production of nitric acid, and in the manufacture of various other chemicals and materials, including nylon.
Workbook solutions (Concise/Selina)
Intext Questions and Answers I
1. (a) State the type of bonding present in ammonia, show by a diagram.
Answer: Ammonia has covalent bonding. The Lewis diagram or dot diagram shows a lone pair on the nitrogen atom and three shared pairs of electrons with three hydrogen atoms.
(b) What is the formula of liquid ammonia ? Account for the basic nature of this compound.
Answer: The formula of liquid ammonia is NH₃. Its aqueous solution is a weak base; the basic nature is due to a lone pair of electrons on its nitrogen atom. An aqueous solution of ammonia [NH₄OH] is a weak base. It dissociates partially to give hydroxyl ions [OH⁻].
2. (a) Write a balanced chemical equation for the lab preparation of ammonia. (2018)
Answer: The balanced chemical equation for the lab preparation of ammonia is:
2NH₄Cl + Ca(OH)₂ → CaCl₂ + 2H₂O + 2NH₃↑
(b) How is ammonia dried and collected in the laboratory?
Answer: In order to get dry ammonia, the gas is passed through a drying tower containing lumps of quicklime (CaO). Ammonia gas is collected in inverted gas jars by the downward displacement of air.
(c) Ammonia cannot be collected over water. Give reason.
Answer: Ammonia cannot be collected over water because it is highly soluble in water.
3. (a) Explain with a diagram the preparation of aqueous ammonia.
Answer: An aqueous solution of ammonia is prepared by dissolving ammonia in water. The rate of dissolution of ammonia in water is very high, therefore, back suction of water is possible. To avoid this, a funnel is attached to the outer end of the delivery tube with rubber tubing. Water is taken in a container and only a small portion of the mouth of the funnel is dipped in water. As ammonia dissolves in water at a higher rate than its production in the flask, the pressure in the funnel above water level decreases for a moment, and water rushes into the funnel. As a result, the rim of the funnel loses its contact with water. Since, ammonia produced pushes the water down, the funnel comes in contact with water again. In this way, ammonia dissolves in water without back suction of water.
(b) Why drying agents such as, P₂O₅ and CaCl₂ are not used to dry NH₃?
Answer: Drying agents like phosphorous pentoxide (P₂O₅) and anhydrous calcium chloride (CaCl₂) are not used to dry NH₃ because ammonia, being basic, reacts with them.
6NH₃ + P₂O₅ + 3H₂O → 2(NH₄)₃PO₄ (ammonium phosphate)
CaCl₂ + 4NH₃ → CaCl₂.4NH₃ (addition compound)
4. A substance ‘A’ was heated with slaked lime and a gas ‘B’ with a pungent smell was obtained. Name the substances A and B and give a balanced equation.
Answer: Substance ‘A’ is an ammonium salt, for example, ammonium chloride (NH₄Cl). Gas ‘B’ is ammonia (NH₃).
A balanced equation is: 2NH₄Cl(s) + Ca(OH)₂(s) → CaCl₂(s) + 2H₂O + 2NH₃↑
5. Ammonia is manufactured by Haber Process.
(a) Under what conditions do the reactants combine to form ammonia ? Give a balanced equation for the reaction.
Answer: The favourable conditions for reactants to combine to form ammonia in Haber’s Process are:
Temperature: Optimum temperature is 450-500 °C.
Pressure: Above 200 atm. (Practically, a pressure of about 250 atm. is used).
Catalyst: Finely divided iron.
Promoter: Traces of molybdenum or Al₂O₃.
The balanced equation for the reaction is: N₂ + 3H₂ ⇌ 2NH₃ + heat.
(b) In what ratio by volume, are the above gases used?
Answer: Nitrogen and hydrogen are used in the ratio of 1:3 by volume.
(c) State one possible source of each reactant used in Haber Process.
Answer: Nitrogen gas is obtained by fractional distillation of liquid air. Hydrogen gas is obtained from water gas (Bosch process) or from natural gas.
(d) State whether the formation of ammonia is promoted by the use of high pressure or low pressure?
Answer: Four volumes of reactants produce two volumes of product, hence high pressure favours the formation of ammonia.
(e) Mention two possible ways by which ammonia produced is removed from unchanged gases.
Answer: Ammonia is separated from the unreacted nitrogen and hydrogen by:
- Liquefaction — Ammonia is liquified easily as compared to nitrogen and hydrogen.
- Absorbing in water because NH₃ is highly soluble in water, while N₂ and H₂ are very slightly soluble.
(f) What is the function of:
(i) finely divided iron,
Answer: Finely divided iron is used as a catalyst. The speed of the reaction can be improved by using a catalyst, which is finely divided iron, obtained by the reduction of iron oxide. Finely divided catalyst has more surface area, this increases the efficiency of the catalyst.
(ii) molybdenum in the above process?
Answer: Molybdenum or Al₂O₃ is used as a promoter to increase the efficiency of the catalyst.
(g) What is the percentage formation of ammonia?
Answer: About 15% of the reacting gases get converted to ammonia in a single pass.
(h) How can this percentage formation be increased ?
Answer: The unchanged nitrogen and hydrogen are recirculated through the plant to get more ammonia. By re-circulating in this way, an eventual yield of 98% can be achieved.
6. Give reasons:
(a) Ammonium compounds do not occur as minerals.
Answer: Ammonia and ammonium compounds being highly soluble in water, do not occur as minerals.
(b) Ammonium nitrate is not used in the preparation of ammonia.
Answer: Though all ammonium salts, on heating with alkalies give NH₃, yet NH₄NO₃ (explosive in nature) on warming with alkalies do not produce ammonia because it decomposes on heating: NH₄NO₃ → N₂O + 2H₂O.
(c) Conc H₂SO₄ is a good drying agent, yet it is not used to dry NH₃.
Answer: Conc. H₂SO₄ is not used to dry NH₃ because ammonia, being basic, reacts with it: 2NH₃ + H₂SO₄ → (NH₄)₂SO₄.
(d) In the lab. preparation of ammonia
(i) calcium hydroxide is used in excess.
Answer: In the lab preparation of ammonia, excess of calcium hydroxide is mixed well with ammonium chloride. A higher ratio by weight of the alkali is used as it may counteract the loss by sublimation of NH₄Cl.
(ii) Flask is fitted in slanting position.
Answer: In the lab preparation of ammonia, the flask is fitted in a slanting position, mouth downwards. The flask is tilted in such a way that the water formed in the reaction does not trickle back into the heated flask and thus break it.
7. State the following conditions required in the Habers process
(a) Temperature
(b) Pressure
(c) Catalyst
Answer: The conditions required in the Haber’s process are:
(a) Temperature: Optimum temperature is 450-500 °C.
(b) Pressure: Above 200 atm. (Practically, a pressure of about 250 atm. is used).
(c) Catalyst: Finely divided iron.
8. Choose the correct word or phrase from the brackets to complete the following sentences and write balanced equations for the same.
(a) Ammonium chloride is a soluble salt prepared by …………….. [precipitation, neutralization].
Answer: Ammonium chloride is a soluble salt prepared by neutralization.
NH₃ (gas) + HCl (gas) → NH₄Cl (solid)
or
NH₄OH [aq.] + HCl → NH₄Cl + H₂O
(b) When ammonium chloride is heated, it undergoes ……………….(thermal decomposition/dissociation).
Answer: When ammonium chloride is heated, it undergoes thermal dissociation.
NH₄Cl ⇌ NH₃ + HCl
(c) Heating ammonium chloride with sodium hydroxide produces …………….. [ammonia, nitrogen].
Answer: Heating ammonium chloride with sodium hydroxide produces ammonia.
NH₄Cl(s) + NaOH(s) → NaCl(s) + H₂O + NH₃↑
9. An element has 2 electrons in its N shell. It reacts with a non-metal of atomic number 7. The compound formed reacts with warm water and produces a basic gas. Identify the elements and write the balanced chemical reactions.
Answer:
Given:
An element (let’s call it X) has 2 electrons in its N shell.
A non-metal (let’s call it Y) has an atomic number of 7.
The compound formed by X and Y reacts with warm water to produce a basic gas.
To find:
- Identify element X and element Y.
- Write the balanced chemical reaction for the formation of the compound.
- Write the balanced chemical reaction of the compound with warm water.
Solution:
Step 1: Identification of the Elements
(i) Identifying Element X (The Metal):
The electron shells are designated as K, L, M, N, corresponding to the principal quantum numbers n = 1, 2, 3, 4.
The element has 2 electrons in its N shell (n=4). This means the inner shells (K, L, M) are completely filled according to the 2, 8, 8 rule for the first 20 elements.
- K shell (n=1) = 2 electrons
- L shell (n=2) = 8 electrons
- M shell (n=3) = 8 electrons
- N shell (n=4) = 2 electrons (as given)
Total number of electrons = Atomic Number (Z)
=> Z = 2 + 8 + 8 + 2 = 20.
The element with atomic number 20 is Calcium (Ca). It is a metal.
(ii) Identifying Element Y (The Non-metal):
It is given that the atomic number of the non-metal is 7.
The element with atomic number 7 is Nitrogen (N).
Step 2: Formation of the Compound and its Balanced Chemical Reaction
Calcium (Ca) is in Group 2, so it loses 2 electrons to form a cation with a valency of +2 (Ca²⁺).
Nitrogen (N) has an electronic configuration of 2, 5. It needs 3 electrons to complete its octet, so it gains 3 electrons to form an anion with a valency of -3 (N³⁻).
To form a neutral compound, we use the criss-cross method for valencies:
- Element: Ca N
- Valency: +2 -3
- Formula: Ca₃N₂
The compound formed is **Calcium Nitride (Ca₃N₂) **.
The balanced chemical reaction for its formation is:
3Ca(s) + N₂(g) → Ca₃N₂(s)
Step 3: Reaction with Warm Water and its Balanced Chemical Reaction
The problem states that the compound (Calcium Nitride) reacts with warm water to produce a basic gas. Metal nitrides react with water to form the corresponding metal hydroxide and ammonia gas. Ammonia (NH₃) is a well-known basic gas.
The products are Calcium Hydroxide (Ca(OH)₂) and Ammonia (NH₃).
The balanced chemical reaction is:
Ca₃N₂(s) + 6H₂O(l) → 3Ca(OH)₂(aq) + 2NH₃(g)
10. The following reactions are carried out :
The following reactions are carried out
A: Nitrogen + metal ⟶ compound X.
B: X + water ⟶ ammonia + another compound.
C: Ammonia + metal oxide ⟶ metal + water + N2
One metal that can be used for reaction A is magnesium.
(a) Write the formula of the compound X formed
(b) Write the correctly balanced equation for reaction B where X is the compound formed.
(c) What property of ammonia is demonstrated by reaction C ?
Answer: (a) The formula of the compound X, which is magnesium nitride, is Mg3N2.
(b) The correctly balanced equation for reaction B is:
Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3↑
(c) Reaction C demonstrates that ammonia is a reducing agent. Ammonia reduces heated metallic oxides to give metals, water vapour and nitrogen.
11. Correct the following:
(a) A reddish brown precipitate is obtained when ammonium hydroxide is added to ferrous sulphate.
Answer: A dirty green precipitate is obtained when ammonium hydroxide is added to ferrous sulphate. [FeSO₄ + 2NH₄OH → (NH₄)₂SO₄ + Fe(OH)₂↓ (Dirty green)]
(b) Liquid ammonia is a solution of NH₃.
Answer: Liquid ammonia is dry ammonia liquefied by applying high pressure. (Aqueous solution of ammonia or Liquor ammonia fortis is a solution of NH₃ in water).
(c) Finely divided platinum is used in Haber Process.
Answer: Finely divided iron is used in Haber Process.
(d) Conc. H₂SO₄ is a drying agent for NH₃.
Answer: Conc. H₂SO₄ is not a drying agent for NH₃ as it reacts with ammonia. Quicklime (CaO) is a drying agent for NH₃.
(e) Ammonium salts, on heating, decompose to give ammonia.
Answer: Ammonium salts, on heating with alkalies, give ammonia. (Some ammonium salts like ammonium chloride on heating undergo thermal dissociation to give ammonia, e.g., NH₄Cl ⇌ NH₃ + HCl. Others like ammonium nitrate decompose to N₂O and H₂O).
12. Choose the correct option from the following :
Ammonia can be obtained by adding water to
A : Ammonium chloride,
B : Ammonium nitrite,
C : Magnesium nitride,
D : Magnesium nitrate.
Answer: C : Magnesium nitride.
(Mg₃N₂ + 6H₂O → 3Mg(OH)₂ + 2NH₃↑)
Exercise
MCQs
1. The catalyst used in Haber’s process is :
(a) Molybdenum
(b) Platinum
(c) Nickel
(d) Iron
Answer: (d) Iron
2. Nitrogen gas can be obtained by heating :
(a) Ammonium nitrate
(b) Ammonium nitrite
(c) Magnesium nitride
(d) Ammonium chloride
Answer: (b) Ammonium nitrite
3. Ammonia can be obtained by adding water to:
(a) NH₄Cl
(b) Mg₃N₂
(c) Mg(NO₃)₂
(d) (NH₄)₂SO₄
Answer: (b) Mg₃N₂
4. The gas collected by downward displacement of air is :
(a) HCl
(b) NH₃
(c) CO₂
(d) H₂S
Answer: (b) NH₃
5. In the Haber’s process, the ratio of reactants nitrogen and hydrogen is :
(a) 2:3
(b) 3:2
(c) 1:3
(d) 3:1
Answer: (c) 1:3
6. When ammonia reacts with an excess of chlorine, the main product formed is :
(a) NH₄Cl
(b) NCl₃
(c) Cl₂
(d) HCl
Answer: (b) NCl₃
7. Ammonia is used in :
(a) Contact process
(b) Haber’s process
(c) Ostwald process
(d) Bayer’s process
Answer: (c) Ostwald process
8. In the following set up for burning ammonia in oxygen, ammonia tube is fitted higher and oxygen tube is kept lower because ?
P Oxygen is lighter than ammonia.
Q Ammonia is lighter than oxygen.
R Ammonia and oxygen mixture is explosive and by keeping them in this position, limited oxygen will react with ammonia.
Which of the following is true ?
(a) Only P
(b) Only Q
(c) Only R
(d) Both P and Q
Answer: (c) Only R
9. Assertion (A): Ammonia does not conduct electricity in gaseous or liquid state.
Reason (R): Ions in ammonia gas or liquid ammonia are not free to move.
(a) (1) Both A and R are true and R is the correct explanation of A.
(b) (2) Both A and R are true but R is not the correct explanation of A.
(c) (3) A is true but R is false.
(d) (4) A is false but R is true.
Answer: (c) (3)
10. Assertion (A): Ammonia is dried by passing through a drying tower containing CaO.
Reason (R): Ammonia being basic in nature reacts with other drying agents.
(a) (1) Both A and R are true and R is the correct explanation of A.
(b) (2) Both A and R are true but R is not the correct explanation of A.
(c) (3) A is true but R is false.
(d) (4) A is false but R is true.
Answer: (a) (1)
11. Assertion (A): Ammonia and its compounds do not occur in minerals.
Reason (R): Ammonia is not soluble in water.
(a) (1) Both A and R are true and R is the correct explanation of A.
(b) (2) Both A and R are true but R is not the correct explanation of A.
(c) (3) A is true but R is false.
(d) (4) A is false but R is true.
Answer: (c) (3)
12. Assertion (A): In the preparation of ammonia, hydrogen is obtained by Bosch process.
Reason (R) : Hydrogen and nitrogen are used in the ratio 1 : 3.
(a) (1) Both A and R are true and R is the correct explanation of A.
(b) (2) Both A and R are true but R is not the correct explanation of A.
(c) (3) A is true but R is false.
(d) (4) A is false but R is true.
Answer: (c) (3)
13. Assertion (A): Haber’s process is used to manufacture ammonia.
Reason (R): The catalyst used in this process is vanadium oxide or platinum.
(a) (1) Both A and R are true and R is the correct explanation of A.
(b) (2) Both A and R are true but R is not the correct explanation of A.
(c) (3) A is true but R is false.
(d) (4) A is false but R is true.
Answer: (c) (3)
14. Assertion (A): Ammonia is recovered by liquification process in Haber’s process.
Reason (R): Nitrogen and hydrogen liquify with difficulty as compared to ammonia.
(a) (1) Both A and R are true and R is the correct explanation of A.
(b) (2) Both A and R are true but R is not the correct explanation of A.
(c) (3) A is true but R is false.
(d) (4) A is false but R is true.
Answer: (a) (1)
15. Assertion (A): Liquid ammonia is used as a refrigerant in ice plants.
Reason (R): CFC, the main refrigerant, causes global warming.
(a) (1) Both A and R are true and R is the correct explanation of A.
(b) (2) Both A and R are true but R is not the correct explanation of A.
(c) (3) A is true but R is false.
(d) (4) A is false but R is true.
Answer: (b) (2)
Very Short Answer Type
1. Name:
(a) the gas which is prepared by Haber’s Process?
Answer: The gas prepared by Haber’s Process is Ammonia.
(b) two gases which produce dense white fumes when reacted with ammonia.
Answer: Two gases which give dense white fumes with ammonia are Hydrogen chloride gas and Chlorine gas.
(c) one salt of ammonia used in:
- (i) dry cell
- (ii) explosives
- (iii) medicine
Answer: One salt of ammonia in each case which is used in:
(i) dry cell is Ammonium chloride.
(ii) explosives is Ammonium nitrate.
(iii) medicine is Ammonium carbonate, used as smelling salt.
(d) an acidic gas which reacts with a basic gas to liberate a neutral gas. Explain briefly.
Answer: An acidic gas which reacts with a basic gas liberating a neutral gas is Hydrogen chloride (when ammonia reacts with chlorine, nitrogen gas is liberated and hydrogen chloride is formed which reacts with excess ammonia).
(e) a metallic chloride that is soluble in ammonium hydroxide.
Answer: A metallic chloride soluble in ammonium hydroxide is Zinc chloride (as its hydroxide, Zn(OH)₂, dissolves in excess ammonium hydroxide).
(f) the gas is obtained when ammonia burns in an atmosphere of oxygen without any catalyst?
Answer: The gas obtained when ammonia burns in an atmosphere of oxygen without any catalyst is Nitrogen (and water vapour).
(g) a nitride of a divalent metal that liberates ammonia when reacted with warm water.
Answer: A nitride of a divalent metal which reacts with warm water liberating ammonia is Magnesium nitride (Mg₃N₂).
(h) an amphoteric oxide that can be reduced by the basic gas ammonia.
Answer: An amphoteric oxide reduced by the basic gas (ammonia) is Lead monoxide (PbO).
(i) a white salt formed by the reaction of an acidic gas and a basic gas.
Answer: A white salt produced by an acidic gas (like HCl) and a basic gas (like NH₃) is Ammonium chloride (NH₄Cl).
(j) The gas burns in oxygen with a greenish-yellow flame?
Answer: The gas that burns in oxygen with a greenish yellow flame is Ammonia.
(k) The gas is produced when excess ammonia reacts with chlorine?
Answer: The gas produced when excess ammonia reacts with chlorine is Nitrogen.
(l) The white crystalline solid, soluble in water, which releases a pungent-smelling gas when heated with sodium hydroxide solution.
Answer: The white crystalline solid that is soluble in water which liberates a pungent smelling gas when heated with sodium hydroxide solution is an ammonium salt like Ammonium chloride.
(m) An alkaline gas which produces dense white fumes when reacted with HCl gas.
Answer: An alkaline gas which produces dense white fumes when reacted with HCl gas is Ammonia.
2. Fill in the blank from the choices given in bracket:
(a) Ammonia gas is collected by ………….. (upward displacement of air, downward displacement of water, downward displacement of air).
(b) Ammonia reacts with excess chorine to form …………… (nitrogen / nitrogen trichloride / ammonium chloride).
Answer: (a) Ammonia gas is collected by downward displacement of air.
(b) Ammonia reacts with excess chlorine to form nitrogen trichloride.
3. Complete the blanks (i) to (v) in the passage given, using the following words.
[Ammonium, reddish brown, hydroxyl, nitrogen dioxide, ammonia, dirty green, alkaline, acidic].
In the presence of a catalyst nitrogen and hydrogen combine to give (i) …………………… gas. When the same gas is passed through water it forms a solution, which will be (ii) …………………… in nature, and will contain the ions (iii) …………………… and (iv) ……………………. A (v) …………………… coloured precipitate of iron [II] hydroxide is formed when the above solution is added to iron [II] sulphate solution.
Answer: In the presence of a catalyst nitrogen and hydrogen combine to give (i) ammonia gas. When the same gas is passed through water it forms a solution, which will be (ii) alkaline in nature, and will contain the ions (iii) ammonium and (iv) hydroxyl. A (v) dirty green coloured precipitate of iron [II] hydroxide is formed when the above solution is added to iron [II] sulphate solution.
4. Name the gas evolved when the following mixtures are heated.
(a) calcium hydroxide and ammonium chloride.
(b) Sodium nitrite and ammonium chloride.
Answer: (a) When calcium hydroxide and ammonium chloride are heated, the gas evolved is Ammonia (NH₃).
(b) When sodium nitrite and ammonium chloride are heated (forming ammonium nitrite in situ, which then decomposes), the gas evolved is Nitrogen (N₂).
5. Name a compound prepared by ammonia and is used as:
Answer: (a) An explosive prepared from ammonia is Ammonium nitrate.
(b) A fertilizer prepared from ammonia is Urea (or ammonium sulphate, ammonium nitrate).
(c) A medicine (smelling salt) prepared from ammonia is Ammonium carbonate.
(d) A laboratory reagent prepared from ammonia is Ammonium hydroxide (ammonia solution).
6. From the list of gases – ammonia, ethane, hydrogen chloride, hydrogen sulphide, select the gas which is used as a reducing agent in reducing copper oxide to copper.
Answer: The gas from the list which is used as a reducing agent in reducing copper oxide to copper is Ammonia.
Short Answer Type
1. Pick the odd member from the list giving reasons:
(a) Ammonia, sulphur dioxide, hydrogen chloride, carbon dioxide.
Answer: The odd member is ammonia.
Reason: Ammonia is alkaline in nature, while sulphur dioxide, hydrogen chloride, and carbon dioxide are generally acidic gases. Ammonia has an alkaline nature and its aqueous solution is a weak base, reacting with acids like hydrogen chloride.
(b) Copper oxide, aluminium oxide, sodium oxide, magnesium oxide.
Answer: The odd member is aluminium oxide.
Reason: Aluminium oxide (Al2O3) is used as a promoter in the Haber’s process for ammonia synthesis and is an amphoteric oxide. Copper oxide is reduced by ammonia, while sodium oxide and magnesium oxide are basic oxides not highlighted for such specific roles or reactions with ammonia in the provided text in the same manner as CuO or Al2O3’s role as a promoter. The most distinct chemical classification is that aluminium oxide is amphoteric, whereas the others are primarily basic oxides.
2. A gas ‘P’ gives dense white fumes with chlorine. Its aqueous solution gives a blue colour with copper (II) hydroxide. Give the name and formula of the gas P.
Answer: The gas ‘P’ is Ammonia. Its formula is NH3.
Ammonia gas reacts with chlorine to produce white fumes of ammonium chloride. An aqueous solution of ammonia (ammonium hydroxide) initially forms a pale blue precipitate of copper(II) hydroxide with copper(II) salts, which then dissolves in excess ammonium hydroxide to give a deep blue solution (due to the formation of tetraamine copper [II] complex), consistent with “gives a blue colour with copper (II) hydroxide”.
3. Copy and complete the following equations.
(a) AIN + H₂O →
Answer: AIN + 3H2O → Al(OH)3 + NH3↑
(b) 2NH₃ + 3PbO →
Answer: 2NH3 + 3PbO → 3Pb + 3H2O + N2↑
(c) NH₃ + 3Cl₂ →
Answer: NH3 + 3Cl2 → NCl3 + 3HCl (when chlorine is in excess)
(d) NH₃ + CO₂ →
Answer: 2NH3 + CO2 → NH2CONH2 + H2O (This reaction occurs at 150°C and 150 atm pressure to form urea)
(i) Which property of ammonia is illustrated by equation (c)?
Answer: Equation (c) (NH3 + 3Cl2 → NCl3 + 3HCl) illustrates that ammonia acts as a reducing agent (as nitrogen in ammonia is oxidized from -3 to +3 in NCl3, and chlorine is reduced). These reactions with chlorine show ammonia is a reducing agent.
(ii) What important fertiliser is prepared from equation (d)? State the conditions.
Answer: The important fertiliser prepared is urea (NH2CONH2). The conditions required are a temperature of 150°C and a pressure of 150 atm.
4. (a) What do you observe when ammonium hydroxide is added to the aqueous solution of:
(i) FeSO₄
Answer: When ammonium hydroxide is added to an aqueous solution of FeSO₄, a dirty green precipitate of ferrous hydroxide, Fe(OH)2, is formed. This precipitate is insoluble in excess ammonium hydroxide.
(ii) Iron (iii) chloride.
Answer: When ammonium hydroxide is added to an aqueous solution of Iron (III) chloride, a reddish brown precipitate of ferric hydroxide, Fe(OH)3, is formed. This precipitate is insoluble in excess ammonium hydroxide.
(iii) Lead nitrate,
Answer: When ammonium hydroxide is added to an aqueous solution of lead nitrate, a white precipitate of lead hydroxide, Pb(OH)2, is formed. This precipitate is insoluble in excess ammonium hydroxide.
(iv) Zinc nitrate ?
Answer: When ammonium hydroxide is added to an aqueous solution of zinc nitrate, a white gelatinous precipitate of zinc hydroxide, Zn(OH)2, is formed. This precipitate is soluble in excess ammonium hydroxide.
(b) Write balanced equation for Q. 4(a).
Answer: The balanced equations for the reactions in Q. 4(a) are:
(i) FeSO₄ + 2NH₄OH → (NH₄)₂SO₄ + Fe(OH)₂↓
(ii) FeCl₃ + 3NH₄OH → 3NH₄Cl + Fe(OH)₃↓
(iii) Pb(NO₃)₂ + 2NH₄OH → 2NH₄NO₃ + Pb(OH)₂↓
(iv) Zn(NO₃)₂ + 2NH₄OH → 2NH₄NO₃ + Zn(OH)₂↓
5. When ammonium hydroxide is added to solution B, a pale blue precipitate is formed. This pale blue precipitate dissolves in excess ammonium hydroxide giving an inky blue solution. What is the cation [positive ion] present in solution B? What is the probable colour of solution B.
Answer: The cation [positive ion] present in solution B is the copper(II) ion (Cu²⁺). The probable colour of solution B (which contains copper(II) ions, such as copper(II) sulphate solution) is blue.
6. Write the equation for the action of heat on :
(a) Ammonium chloride,
Answer: NH4Cl(s) ⇌ NH3(g) + HCl(g)
(b) Ammonium nitrate.
Answer: NH4NO3(s) → N2O(g) + 2H2O(g)
State whether each reaction is an example of thermal decomposition or thermal dissociation.
Answer: The heating of ammonium chloride is an example of thermal dissociation.
The heating of ammonium nitrate is an example of thermal decomposition.
7. Name two gases which can be used to study the fountain experiment. State the common property demonstrated by the fountain experiment.
Answer: Two gases that can be used to study the fountain experiment are ammonia (NH3) and hydrogen chloride (HCl). The common property demonstrated by the fountain experiment is the high solubility of the gas in water.
8. Name the other ion formed when ammonia dissolves in water. Give one test that can be used to detect the presence of the ion produced.
Answer: When ammonia dissolves in water, it forms ammonium ions (NH4⁺) and hydroxide ions (OH⁻). The other ion formed, responsible for the alkaline nature, is the hydroxide ion (OH⁻). A test to detect the presence of hydroxide ions is that the solution turns moist red litmus paper blue, or it turns phenolphthalein solution pink.
9. State the conditions required for: Catalytic oxidation of ammonia to nitric oxide.
Answer: The conditions required for the catalytic oxidation of ammonia to nitric oxide are the presence of a platinum (Pt) catalyst and a temperature of 800°C.
10. Give reasons for the following:
(a) Liquid ammonia is used as a refrigerant in ice plants.
Answer: Liquid ammonia is used as a refrigerant in ice plants because it takes a lot of energy to vaporize (high latent heat of vaporization). This heat is absorbed from the surrounding bodies, which are consequently cooled down. It evaporates rapidly and produces a cooling effect.
(b) Aqueous solution of ammonia is used for removing grease stains from woollen clothes.
Answer: Aqueous solution of ammonia is used for removing grease stains from woollen clothes because aqueous NH3 emulsifies or dissolves fats and grease.
(c) Aqueous solution of ammonia gives a pungent smell.
Answer: Aqueous solution of ammonia gives a pungent smell because ammonia gas, which has a strong, pungent, choking smell, is released from the solution.
(d) Aqueous solution of ammonia conducts electricity.
Answer: Aqueous solution of ammonia conducts electricity because ammonia dissolves in water to form ammonium hydroxide (NH4OH), which is a weak electrolyte and dissociates partially to produce mobile ions, namely ammonium ions (NH4⁺) and hydroxide ions (OH⁻).
11. Write balanced chemical equations for the following:
(a) Ammonium hydroxide is added to ferrous sulphate solution.
Answer: FeSO4(aq) + 2NH4OH(aq) → (NH4)2SO4(aq) + Fe(OH)2(s)↓
(b) Magnesium nitride is treated with warm water.
Answer: Mg3N2(s) + 6H2O(l) → 3Mg(OH)2(s) + 2NH3(g)↑ (upon warming)
(c) Ammonium chloride is heated with sodium hydroxide.
Answer: NH4Cl(s) + NaOH(s) → NaCl(s) + H2O(l) + NH3(g)↑ (on heating)
(d) Chlorine reacts with excess of ammonia.
Answer: 8NH3(g) (excess) + 3Cl2(g) → N2(g) + 6NH4Cl(s)
(e) Ammonia and oxygen in the presence of a catalyst.
Answer: 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) + Heat (Catalyst: Pt, Temperature: 800°C)
(f) Reduction of hot copper (II) oxide to copper using ammonia gas.
Answer: 2NH3(g) + 3CuO(s) → 3Cu(s) + 3H2O(g) + N2(g)↑ (on heating)
(g) To illustrate the reducing nature of ammonia
Answer: 2NH3(g) + 3CuO(s) → 3Cu(s) + N2(g) + 3H2O(g) (on heating). In this reaction, ammonia reduces copper(II) oxide to copper.
(h) Lab. preparation of ammonia using an ammonium salt.
Answer: 2NH4Cl(s) + Ca(OH)2(s) → CaCl2(s) + 2H2O(l) + 2NH3(g)↑ (on heating)
(i) Reaction of ammonia with excess of chlorine.
Answer: NH3(g) + 3Cl2(g) (excess) → NCl3(l) + 3HCl(g)
(j) Reaction of ammonia with sulphuric acid.
Answer: 2NH3(g) + H2SO4(aq) → (NH4)2SO4(aq)
(k) When excess of ammonia is treated with chlorine.
Answer: 8NH3(g) (excess) + 3Cl2(g) → N2(g) + 6NH4Cl(s)
12. Write a balanced equation for a reaction in which ammonia is oxidized by:
(a) a metal oxide,
Answer: 2NH3(g) + 3CuO(s) → 3Cu(s) + N2(g) + 3H2O(g) (on heating). Here ammonia is oxidized to nitrogen by copper(II) oxide.
(b) a gas which is not oxygen.
Answer: 8NH3(g) + 3Cl2(g) → N2(g) + 6NH4Cl(s). Here ammonia is oxidized to nitrogen by chlorine gas.
13. Write a relevant equation to show that ammonia acts as a reducing agent.
Answer: A relevant equation showing ammonia acting as a reducing agent is: 2NH3(g) + 3CuO(s) → 3Cu(s) + N2(g) + 3H2O(g) (on heating). In this reaction, ammonia reduces copper(II) oxide to copper.
14. Rewrite the correct statement with the missing word/s: Magnesium nitride reacts with water to liberate ammonia.
Answer: Magnesium nitride reacts with warm water to liberate ammonia.
15. Distinguish between the following (using ammonia solution):
(a) Calcium chloride and zinc chloride.
Answer: When ammonium hydroxide solution is added dropwise and then in excess:
- To zinc chloride solution: A white gelatinous precipitate of zinc hydroxide forms, which dissolves in excess ammonium hydroxide solution.
- To calcium chloride solution: A white precipitate of calcium hydroxide may form (if concentrations are sufficient), which is insoluble in excess ammonium hydroxide solution. The distinct observation is the solubility of the zinc hydroxide precipitate in excess ammonia solution, which does not occur with calcium hydroxide.
(b) Ferric salt and ferrous salt,
Answer: When ammonium hydroxide solution is added:
- To a ferric salt solution (e.g., FeCl3): A reddish brown precipitate of ferric hydroxide (Fe(OH)3) is formed.
- To a ferrous salt solution (e.g., FeSO4): A dirty green precipitate of ferrous hydroxide (Fe(OH)2) is formed.
Both precipitates are insoluble in excess ammonium hydroxide.
(c) Zinc nitrate and lead nitrate.
Answer: When ammonium hydroxide solution is added dropwise and then in excess:
- To zinc nitrate solution: A white gelatinous precipitate of zinc hydroxide forms, which dissolves in excess ammonium hydroxide solution.
- To lead nitrate solution: A white precipitate of lead hydroxide forms, which is insoluble in excess ammonium hydroxide solution.
16. Give balanced equations for the following conversions:
(a) Ammonia to nitrogen using an acidic gas,
Answer: 2NH3(g) + 3Cl2(g) → N2(g) + 6HCl(g). (Chlorine acts as an oxidizing agent, and hydrogen chloride, an acidic gas, is formed. This shows the conversion of ammonia to nitrogen).
(a) Ammonia to nitrogen using an acidic gas,
Answer: 2NH3(g) + 3Cl2(g) → N2(g) + 6HCl(g). (Chlorine acts as an oxidizing agent, and hydrogen chloride, an acidic gas, is formed. This shows the conversion of ammonia to nitrogen).
(b) Ammonia to brown gas,
Answer: Step 1: 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) (Catalyst: Pt, 800°C)
Step 2: 2NO(g) + O2(g) → 2NO2(g) (brown gas)
(c) Ammonia to nitrogen trichloride,
Answer: NH3(g) + 3Cl2(g) (excess) → NCl3(l) + 3HCl(g)
(d) Ammonia solution to an amphoteric hydroxide,
Answer: Zn(NO3)2(aq) + 2NH4OH(aq) → Zn(OH)2(s)↓ + 2NH4NO3(aq). (Zinc hydroxide is an amphoteric hydroxide).
(e) A nitride of a trivalent metal to ammonia,
Answer: AlN(s) + 3H2O(l) → Al(OH)3(s) + NH3(g)↑ (on warming) (Aluminium is a trivalent metal).
(f) Lead oxide to lead.
Answer: 3PbO(s) + 2NH3(g) → 3Pb(s) + 3H2O(g) + N2(g)↑ (on heating)
17. State two relevant observations for: Ammonium hydroxide solution is added to zinc nitrate solution slowly and then in excess.
Answer: (a) When ammonium hydroxide solution is added slowly to zinc nitrate solution, a white gelatinous precipitate is formed.
(b) On adding excess ammonium hydroxide solution, the white gelatinous precipitate dissolves, resulting in a clear solution.
18. Copy and complete the following table relating to important industrial process:
Answer:
19. Distinguish between the following pairs of compounds using the test given in bracket :
(a) Iron [II] sulphate and iron [III] sulphate [using ammonium hydroxide]
Answer: When ammonium hydroxide is added to an aqueous solution of Iron (II) sulphate (FeSO₄), a dirty green precipitate of Iron (II) hydroxide, Fe(OH)₂, is formed. This precipitate is insoluble in excess ammonium hydroxide.
When ammonium hydroxide is added to an aqueous solution of an Iron (III) salt like Iron (III) chloride (FeCl₃), a reddish brown precipitate of Iron (III) hydroxide, Fe(OH)₃, is formed. This precipitate is also insoluble in excess ammonium hydroxide. The distinction is made by the colour of the precipitate formed.
(b) A lead salt and a zinc salt [using excess ammonium hydroxide]
Answer: When ammonium hydroxide is added to an aqueous solution of a lead salt like lead nitrate, Pb(NO₃)₂, a white precipitate of lead hydroxide, Pb(OH)₂, is formed. This precipitate is insoluble in excess ammonium hydroxide.
When ammonium hydroxide is added to an aqueous solution of a zinc salt like zinc nitrate, Zn(NO₃)₂, a white gelatinous precipitate of zinc hydroxide, Zn(OH)₂, is formed. This precipitate is soluble in excess ammonium hydroxide. The distinction is made by the solubility of the white precipitate in excess ammonium hydroxide.
20. State relevant observations for the following:
(a) Ammonia gas is passed over heated copper (II) oxide.
Answer: When ammonia gas is passed over heated copper (II) oxide, the black copper oxide is reduced to reddish brown copper. Nitrogen gas and water vapour are also formed.
(b) In the absence of catalyst, ammonia is burnt in an atmosphere of oxygen.
Answer: In the absence of a catalyst, when ammonia is burnt in an atmosphere of oxygen, ammonia burns with a greenish yellow flame and produces water vapours and nitrogen.
(c) Ammonium hydroxide is first added in a small quantity and then in excess to a solution of copper sulphate.
Answer: When ammonium hydroxide is first added in a small quantity to a solution of copper sulphate, a pale blue precipitate of copper hydroxide is formed. When ammonium hydroxide is added in excess, the pale blue precipitate dissolves, forming an azure blue (deep blue) soluble complex salt, tetraamine copper [II] sulphate.
(d) Water is added to the product formed, when Al is burnt in a jar of nitrogen gas.
Answer: When Al is burnt in a jar of nitrogen gas, aluminium nitride (AlN) is formed. When water (especially warm water) is added to aluminium nitride, ammonia gas, which has a pungent smell, is liberated, and aluminium hydroxide is also formed.
(d) Water is added to the product formed, when Al is burnt in a jar of nitrogen gas.
Answer: When Al is burnt in a jar of nitrogen gas, aluminium nitride (AlN) is formed. When water (especially warm water) is added to aluminium nitride, ammonia gas, which has a pungent smell, is liberated, and aluminium hydroxide is also formed.
(e) Excess of chlorine gas is reacted with ammonia gas.
Answer: When excess of chlorine gas is reacted with ammonia gas, hydrogen chloride and a yellow coloured highly explosive liquid, nitrogen trichloride (NCl3), are formed.
(f) Calcium hydroxide is heated with ammonium chloride crystals.
Answer: When calcium hydroxide is heated with ammonium chloride crystals, ammonia gas is evolved, which has a pungent, choking smell. This gas turns moist red litmus paper blue
Long Answer Type
1. (a) Is ammonia more dense or less dense than air?
Answer: Ammonia is less dense than air. The vapour density of NH3 is 8.5, while that of air is 14.4, indicating ammonia is lighter than air
(b) What property of ammonia is demonstrated by the Fountain Experiment?
Answer: The Fountain Experiment is used to demonstrate the high solubility of ammonia gas in water.
(c) Write the balanced equation for the reaction between ammonia and sulphuric acid.
Answer: The balanced equation for the reaction between ammonia and sulphuric acid is:
2NH3 + H2SO4 → (NH4)2SO4
(c) Write the balanced equation for the reaction between ammonia and sulphuric acid.
Answer: The balanced equation for the reaction between ammonia and sulphuric acid is:
2NH3 + H2SO4 → (NH4)2SO4
2. Ammonia solution in water gives a blue precipitate when it combines with a solution of copper salt. The blue precipitate further dissolves in excess of ammonia solution to give an azure blue solution. Explain with equation.
Answer: When ammonia solution in water, which is ammonium hydroxide (NH4OH), is added to a solution of a copper salt such as copper sulphate (CuSO4), a pale blue precipitate of copper hydroxide Cu(OH)2 is formed.
The equation is: CuSO4 + 2NH4OH → (NH4)2SO4 + Cu(OH)2↓ (pale blue)
This pale blue precipitate of copper hydroxide dissolves in excess of ammonium hydroxide. This occurs because the copper hydroxide reacts with the excess ammonium hydroxide and the ammonium sulphate already present to form a soluble complex salt, tetraamine copper [II] sulphate, which has an azure blue (deep blue) colour.
The equation for the dissolution is: Cu(OH)2 + (NH4)2SO4 + 2NH4OH → [Cu(NH3)4]SO4 + 4H2O (azure blue solution)
3. Give chemical equation(s) to prove that NH3 contains nitrogen and hydrogen.
Answer: The presence of nitrogen and hydrogen in ammonia (NH3) can be proven by the following reactions:
(i) Burning of ammonia in oxygen: When ammonia burns in oxygen, it produces water vapours and nitrogen. This shows that ammonia contains nitrogen and hydrogen.
4NH3 + 3O2 → 2N2 + 6H2O
(ii) Reduction of metallic oxides: When ammonia gas is passed over heated copper (II) oxide, the black copper oxide is reduced to reddish brown copper, and water vapour and nitrogen gas are formed. The formation of nitrogen and water (containing hydrogen) proves that ammonia is made up of nitrogen and hydrogen.
2NH3 + 3CuO → 3Cu + 3H2O + N2↑
4. When an ammonium salt is warmed with sodium hydroxide solution, a gas is evolved. State three ways in which you could identify this gas.
Answer: The gas evolved when an ammonium salt is warmed with sodium hydroxide solution is ammonia (NH3). Three ways to identify this gas are:
(i) Odour: Ammonia gas has a sharp, characteristic pungent choking smell.
(ii) Effect on litmus paper: Ammonia gas is alkaline in nature and turns moist red litmus paper blue. It also turns moist turmeric paper brown or phenolphthalein solution pink.
(iii) Reaction with hydrogen chloride gas: When a glass rod dipped in concentrated hydrochloric acid is brought near ammonia gas, dense white fumes of ammonium chloride are formed. The reaction is: NH3 + HCl → NH4Cl.
5. A gas ‘A’ reacts with another gas ‘B’ in the presence of a catalyst to give a colourless gas ‘C’. The gas ‘C’ when comes in contact with air produces a brown gas ‘D’. The solution of ‘A’ in water turns red litmus blue. Explain the observations.
Answer: The observations can be explained as follows:
The gas ‘A’ whose solution in water turns red litmus blue is ammonia (NH3), as ammonia is an alkaline gas.
Gas ‘A’ (ammonia) reacts with another gas ‘B’ (oxygen) in the presence of a catalyst (platinum) at about 800°C to give a colourless gas ‘C’, which is nitric oxide (NO). This is the catalytic oxidation of ammonia.
4NH3 (A) + 5O2 (B) –(Pt, 800°C)–> 4NO (C) + 6H2O
The colourless gas ‘C’ (nitric oxide) when it comes in contact with air (oxygen) is oxidized to produce a brown gas ‘D’, which is nitrogen dioxide (NO2).
2NO (C) + O2 (from air) → 2NO2 (D) (brown gas)
The observations are:
- The solution of gas ‘A’ (ammonia) in water is alkaline, hence it turns red litmus paper blue.
- Gas ‘C’ (nitric oxide) formed is a colourless gas.
- Gas ‘D’ (nitrogen dioxide) formed when gas ‘C’ comes in contact with air is a brown gas.
- During the catalytic oxidation of ammonia to nitric oxide, the platinum catalyst continues to glow even after heating is discontinued because the reaction is exothermic.
6. (a) Name the common refrigerant. How does it deplete ozone layer?
Answer: A common type of refrigerant mentioned is freon, which is a chlorofluorocarbon (CFC).
Chlorofluorocarbons (CFCs) deplete the ozone layer. The chlorofluoro carbons are decomposed by the ultraviolet rays from the sun to highly reactive chlorine which is produced in the atomic form (free radical).
CF2Cl2(g) –Ultraviolet–> CF2Cl(g) + Cl(g) (free radical)
This free radical chlorine [Cl] reacts with ozone (O3) to form chlorine monoxide (ClO) and oxygen (O2).
Cl(g) + O3(g) → ClO(g) + O2(g)
This reaction causes the depletion of ozone. Chlorine monoxide further reacts with atomic oxygen (O) present in the atmosphere, which produces more free chlorine radicals.
ClO(g) + O(g) → Cl(g) + O2(g)
This free radical [Cl] again destroys ozone, and the process continues, thereby giving rise to ozone depletion.
(b) What is the alternative of chlorofluorocarbons?
Answer: Suitable alternatives for chlorofluorocarbons are those which are non-ozone depleting. Ammonia itself is an environmentally compatible refrigerant that does not deplete the ozone layer.
(c) State the advantages and disadvantages of using ammonia as refrigerant?
Answer: Advantages of Ammonia as refrigerant:
(i) Ammonia is environmentally compatible. It does not deplete ozone layer and does not contribute towards the global warming.
(ii) It has superior thermodynamic qualities; as a result, ammonia refrigeration systems use less electricity.
(iii) Ammonia has a recognizable odour, and so leaks are not likely to escape detection. Being lighter than air, it goes up in the atmosphere, not affecting life too much on earth in case of small leaks.
Disadvantages of Ammonia as refrigerant:
(i) It is not compatible with copper, so it cannot be used in any system with copper pipes.
(ii) Ammonia is poisonous in high concentration.
7. (a) Which feature of ammonia molecule leads to the formation of the ammonium ion when ammonia dissolves in water?
Answer: The feature of the ammonia molecule that leads to the formation of the ammonium ion when ammonia dissolves in water is the lone pair of electrons on its nitrogen atom. This lone pair allows ammonia to act as a weak base and accept a proton.
(b) Name the other ion formed when ammonia dissolves in water.
Answer: When ammonia dissolves in water, it forms ammonium hydroxide (NH4OH), which then partially dissociates to give ammonium ions (NH4+) and hydroxyl ions (OH-). So, the other ion formed is the hydroxyl ion (OH-).
NH3 + H2O ⇌ NH4OH
NH4OH ⇌ NH4+ + OH-
(c) Give one test that can be used to detect the presence of the ion produced in (b).
Answer: The ion produced in (b) is the hydroxyl ion (OH-), which makes the solution alkaline. One test to detect its presence is to use an indicator. For example, the aqueous solution of ammonia will change the colour of:
- Moist red litmus paper to blue.
- Methyl orange solution from orange to yellow.
- Phenolphthalein solution from colourless to pink.
8. (a) Of the two gases, ammonia and hydrogen chloride, which is more dense? Name the method of collection of this gas.
Answer: Ammonia gas has a vapour density of 8.5, while air has a vapour density of 14.4. Thus, ammonia is lighter than air. Hydrogen chloride (HCl) has a molecular mass of 36.5, so its vapour density is 18.25, making it denser than air and also denser than ammonia. Therefore, hydrogen chloride is more dense than ammonia.
The method of collection for the denser gas, hydrogen chloride, is by the upward displacement of air (also known as downward delivery).
(b) Give one example of a reaction between the above two gases which produces a solid compound.
Answer: When ammonia gas reacts with hydrogen chloride gas, they combine to form a white solid compound, ammonium chloride.
NH3(g) + HCl(g) → NH4Cl(s)
9. Study the flow chart given and give balanced equations to represent the reactions A, B and C.
Mg3N2 –(A)–> NH3 –(B)–> NH4Cl
Answer: Reaction A represents the formation of ammonia (NH3) from magnesium nitride (Mg3N2). This occurs when magnesium nitride reacts with warm water.
Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3↑
Reaction B represents the formation of ammonium chloride (NH4Cl) from ammonia (NH3). This occurs when ammonia gas reacts with hydrogen chloride gas.
NH3 + HCl → NH4Cl
Reaction C is not explicitly shown in the provided flowchart originating from NH4Cl. However, a common reaction involving NH4Cl to regenerate ammonia is its reaction with an alkali like sodium hydroxide.
NH4Cl + NaOH → NaCl + H2O + NH3↑
10. With respect to the manufacture of ammonia, answer the following:
(a) Name the process involved.
Answer: The process involved in the manufacture of ammonia is Haber’s Process.
(b) State the ratio of the reactants taken.
Answer: The reactants, nitrogen and hydrogen, are taken in the ratio of 1:3 by volume, respectively.
(c) State the catalyst used.
Answer: The catalyst used is finely divided iron. Traces of molybdenum or Al2O3 are used as a promoter.
(d) Give the equation for the manufacture of the gas – ammonia.
Answer: The equation for the manufacture of ammonia is:
N2 + 3H2 ⇌ 2NH3 + heat
11. The following questions are based on the preparation of ammonia gas in the laboratory:
(a) Explain why ammonium nitrate is not used in the preparation of ammonia.
Answer: Ammonium nitrate (NH4NO3) is not used in the laboratory preparation of ammonia because it is explosive in nature. Furthermore, on heating, ammonium nitrate decomposes to form nitrous oxide (N2O) and water, rather than ammonia.
NH4NO3 –Δ–> N2O + 2H2O
(b) Name the compound normally used as a drying agent during the process.
Answer: The compound normally used as a drying agent for ammonia gas during its laboratory preparation is quicklime (calcium oxide, CaO).
(c) How is ammonia gas collected. Explain why it is not collected over water.
Answer: Ammonia gas is collected in inverted gas jars by the downward displacement of air.
It is not collected over water because ammonia is highly soluble in water (1 volume of water dissolves about 702 volumes of ammonia at 20°C and 1 atm pressure).
12. The diagram below shows the set up for the laboratory preparation of a pungent alkaline gas.
(a) Name the gas collected in the jar.
Answer: The pungent alkaline gas collected in the jar is ammonia (NH3).
(b) Give a balanced equation for the above preparation.
Answer: The balanced equation for the laboratory preparation of ammonia, typically using ammonium chloride and calcium hydroxide, is:
2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + 2NH3↑
(c) State how the above gas is collected.
Answer: The gas (ammonia) is collected by the downward displacement of air. This is because ammonia is lighter than air. The gas jar is held inverted for collection.
13. Answer the following questions with respect to the given figure.
(a) Identify gas P and gas Q.
Answer: Gas P and Gas Q react in Process R to form NH3. Process R is Haber’s process. Therefore, Gas P is Nitrogen (N2) and Gas Q is Hydrogen (H2), or vice versa.
(b) Give a balanced equation to convert ammonia into gas P by a method other than decomposition. State the property of ammonia used in carrying out the conversion.
Answer: Assuming Gas P is Nitrogen (N2). Ammonia can be converted to nitrogen by reacting it with hot copper (II) oxide. This is not simple decomposition (2NH3 → N2 + 3H2).
The balanced equation is: 2NH3 + 3CuO → N2 + 3Cu + 3H2O
In this reaction, ammonia acts as a reducing agent, as it reduces copper (II) oxide to copper.
(c) Name fertiliser S and give a balanced equation for its preparation.
Answer: Fertiliser S is formed from the reaction of NH3 and H2SO4. Fertiliser S is ammonium sulphate.
The balanced equation for its preparation is: 2NH3 + H2SO4 → (NH4)2SO4
(d) Name process T and state the conditions that enable conversion of ammonia to nitric oxide.
Answer: Process T, the conversion of NH3 to NO (nitric oxide), is the catalytic oxidation of ammonia.
The conditions that enable this conversion are:
- Catalyst: Platinum (Pt)
- Temperature: Around 800°C
- Reactant: Oxygen (O2) is also required.
The equation is: 4NH3 + 5O2 –(Pt, 800°C)–> 4NO + 6H2O
(e) Give a balanced equation for the conversion of brown gas to liquid U.
Answer: The brown gas is nitrogen dioxide (NO2), formed from the oxidation of NO. Liquid U is nitric acid (HNO3). The conversion of nitrogen dioxide to nitric acid can be represented by the equation (in the presence of oxygen and water):
4NO2 + O2 + 2H2O → 4HNO3
(f) Name fertiliser A.
Answer: Liquid U is nitric acid (HNO3). Fertiliser A, derived from nitric acid, is likely ammonium nitrate.
(g) Name process R.
Answer: Process R, where Gas P (N2) and Gas Q (H2) combine to form NH3, is the Haber’s Process for the manufacture of ammonia.
14. The diagram given below describes the manufacturing process of a gas.
(a) Name the process.
Answer: The diagram describes the Haber’s Process for the manufacture of ammonia.
(b) Identify A, B and C.
Answer: A is Nitrogen gas (N2).
B is Hydrogen gas (H2).
C is Liquid ammonia (NH3).
(c) State the ratio of A and B.
Answer: The ratio of A (Nitrogen) to B (Hydrogen) used in the process is 1:3 by volume.
(d) Write the equation involved with their respective conditions.
Answer: The equation involved is:
N2(g) + 3H2(g) ⇌ 2NH3(g) + heat
Respective conditions are:
- Temperature: Optimum temperature is 450-500 °C.
- Pressure: Above 200 atmospheres (practically about 250 atm).
- Catalyst: Finely divided iron.
- Promoter: Traces of molybdenum or Al2O3.
(e) How is the product separated from unreacted reactants?
Answer: The product, ammonia, is separated from the unreacted nitrogen and hydrogen primarily by liquefaction. Ammonia liquefies easily under high pressure and low temperature in the cooling pipes (condenser), whereas nitrogen and hydrogen do not liquefy easily under these conditions and are recirculated. Ammonia can also be separated by absorbing it in water, as NH3 is highly soluble in water while N2 and H2 are very slightly soluble.
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