Get notes, summary, questions and answers, MCQs, extras, competency-based questions and PDFs of Study of Compounds-Sulphuric Acid: ICSE Class 10 Chemistry (Concise/Selina). However, the notes should only be treated as references, and changes should be made according to the needs of the students.
Summary
Sulphuric acid is a very important chemical compound. Its chemical formula is H2SO4. It is often called the “King of Chemicals” because it is used to make so many other things in many industries. A long time ago, it was known as “oil of vitriol.” This name came about because it was an oily liquid made by heating crystals called green vitriol.
Sulphuric acid can be prepared in a few ways. One method involves oxidizing a water solution of sulphur dioxide using oxygen, chlorine, or bromine. Another way is by reacting sulphur with concentrated nitric acid. For making large amounts, a method called the Contact Process is used. This process has several steps. First, sulphur dioxide gas is made, either by burning sulphur or by roasting iron pyrites. Then, this gas, mixed with air, must be cleaned very well to remove any dust or impurities like arsenic oxide, as these can stop the process from working efficiently.
After cleaning and drying, the sulphur dioxide and oxygen mixture is passed over a catalyst, usually vanadium pentoxide, at a temperature of about 450°C. The catalyst helps sulphur dioxide react with oxygen to form sulphur trioxide. This reaction gives out heat. The sulphur trioxide gas is then absorbed in concentrated sulphuric acid to form a substance called oleum, or pyrosulphuric acid. Sulphur trioxide is not mixed directly with water because this reaction produces a lot of heat and can create a mist of acid that is hard to collect. Finally, the oleum is carefully mixed with water to get sulphuric acid of the desired strength.
Sulphuric acid has different properties depending on whether it is dilute (mixed with a lot of water) or concentrated (has very little water). Pure sulphuric acid is a colorless, odorless, oily liquid. It is denser than water and dissolves in water in all amounts, releasing a lot of heat. It is hygroscopic, meaning it can absorb moisture from the air, so it should be kept in tightly closed bottles.
When dilute, sulphuric acid acts as a typical acid. It reacts with metals that are more reactive than hydrogen to produce hydrogen gas and a metal sulphate. It neutralizes bases (like metal oxides and hydroxides) to form salt and water. It also reacts with metal carbonates and bicarbonates to release carbon dioxide gas, and with metal sulphides to release hydrogen sulphide gas. It reacts with sulphites to release sulphur dioxide gas.
Concentrated sulphuric acid has some special properties. It has a high boiling point, making it a non-volatile acid. This means it can be used to make other acids that are more volatile (evaporate easily), like hydrochloric acid and nitric acid, from their salts. Concentrated sulphuric acid is a strong oxidizing agent, especially when hot. It can oxidize non-metals like carbon and sulphur, and metals like copper. In these reactions, the sulphuric acid itself is reduced to sulphur dioxide. It is also a powerful dehydrating agent, meaning it can remove water from other substances. For example, it removes water from sugar, leaving behind a black mass of carbon. It also removes water from blue copper (II) sulphate crystals, turning them white.
Sulphuric acid has many uses. It is used to make fertilizers, such as ammonium sulphate and superphosphate of lime. It is used in making other chemicals, including hydrochloric acid, nitric acid, dyes, drugs, and explosives like TNT. It is used in metallurgy for extracting metals and for cleaning metal surfaces (pickling). It is also used in lead-acid batteries (like those in cars) and in refining oil.
To test for sulphuric acid or soluble sulphate salts, barium chloride solution is added. If sulphuric acid or a sulphate is present, a white solid (precipitate) of barium sulphate forms. This white solid does not dissolve in strong acids like hydrochloric acid or nitric acid.
Workbook solutions (Concise/Selina)
Intext Questions and Answers I
1. Comment, sulphuric acid is referred to as :
(a) King of chemicals,
(b) Oil of vitriol.
Answer: (a) Sulphuric acid is rightly called the ‘King of Chemicals’ because there is no other manufactured compound which is used by such a large number of key industries.
(b) In the later Middle Ages, sulphuric acid was obtained as an oily viscous liquid by heating crystals of green vitriol, and was, therefore, known by the name of oil of vitriol.
2. Sulphuric acid is manufactured by Contact process.
(a) Give two balanced equations to obtain SO₂ in this process,
(b) Give the conditions for the oxidation of SO₂,
(c) Name the catalyst used.
(d) Why H₂SO₄ is not obtained by directly reacting SO₃ with water?
(e) Name the chemical used to dissolve SO₃ and also name the product formed. Give all the main reactions of this process.
Answer: (a) Two balanced equations to obtain SO₂ in the Contact process are:
- 4FeS₂ (Iron pyrites) + 11O₂ → 2Fe₂O₃ + 8SO₂.
- S + O₂ → SO₂.
(b) The conditions for the oxidation of SO₂ to SO₃ are:
(i) Low temperature: The temperature should be as low as possible. The yield has been found to be maximum at about 410-450°C.
(ii) High pressure: High pressure favours the reaction. Hence the pressure of 1 – 2 atmosphere is used.
(iii) Excess of oxygen: This increases the production of sulphur trioxide.
(iv) A suitable catalyst: Vanadium pentoxide (V₂O₅) or platinum (Pt) is used. The catalyst is initially heated to 450°C.
(c) The catalyst used is vanadium pentoxide (V₂O₅) or platinum (Pt). Vanadium pentoxide is commonly used.
(d) H₂SO₄ is not obtained by directly reacting SO₃ with water because sulphur trioxide does not dissolve in water satisfactorily and it gives a lot of heat and forms misty droplets of sulphuric acid, so it is not directly absorbed by water.
(e) The chemical used to dissolve SO₃ is concentrated sulphuric acid (98%). The product formed is H₂S₂O₇ (oleum or pyrosulphuric acid).
The main reactions of this process are:
- Formation of Sulphur dioxide:
S + O₂ → SO₂; or 4FeS₂ + 11O₂ → 2 Fe₂O₃ + 8SO₂ - Conversion of purified SO₂ to SO₃:
2SO₂ + O₂ –(V₂O₅/Pt, 400-450°C)–> 2SO₃ - Conversion of sulphur trioxide into oleum:
SO₃ + H₂SO₄ → H₂S₂O₇ - Dilution of oleum:
H₂S₂O₇ + H₂O → 2 H₂SO₄.
3. Why the impurity of arsenic oxide must be removed before passing the mixture of SO₂ and air through the catalytic chamber?
Answer: The impurity of arsenic oxide must be removed because it poisons the catalyst, meaning the catalyst loses its efficiency. Platinum, if used as a catalyst, easily gets poisoned by impurities like arsenic (III) oxide.
4.
(a) Name the catalyst which helps in the conversion of sulphur dioxide to sulphur trioxide in step C.
Answer: The catalyst which helps in the conversion of sulphur dioxide to sulphur trioxide in step C is vanadium pentoxide (V₂O₅) or platinum (Pt).
(b) In the Contact process for the manufacture of sulphuric acid, sulphur trioxide is not converted to sulphuric acid by reacting it with water. Instead a two-steps procedure is used. Write the equations for the two steps involved in D.
Answer: The two steps involved in D, where sulphur trioxide is converted to sulphuric acid, are:
SO₃ + H₂SO₄ → H₂S₂O₇ (oleum or pyrosulphuric acid)
H₂S₂O₇ + H₂O → 2H₂SO₄
(c) What type of substance will liberate sulphur dioxide from sodium sulphite in step E?
Answer: An acid (dilute) will liberate sulphur dioxide from sodium sulphite in step E. For example, Na₂SO₃ + H₂SO₄ (dil) → Na₂SO₄ + H₂O + SO₂↑.
(d) Write the equation for the reaction by which sulphur dioxide is converted to sodium sulphite in step F.
Answer: SO₂ + 2NaOH → Na₂SO₃ + H₂O
Exercise
MCQs
1. The gas evolved when dil. sulphuric acid reacts with iron sulphide :
(a) Hydrogen sulphide (b) Sulphur dioxide
(c) Sulphur trioxide
(d) Vapour of sulphuric acid
Answer: (a) Hydrogen sulphide
2. In the given equation-H₂S+H₂SO₄ → S + 2H₂O + SO₂ : Identify the role played by conc. H₂SO₄.
(a) Non-volatile acid
(b) Oxidising agent
(c) Dehydrating agent (d) None of the above
Answer: (b) Oxidising agent
3. Dilute sulphuric acid will produce a white precipitate when added to a solution of:
(a) Copper nitrate
(b) Zinc nitrate
(c) Lead nitrate
(d) Sodium nitrate
Answer: (c) Lead nitrate
4. On passing SO₂ through chlorine water, the acid produced is :
(a) H₂SO₃
(b) HNO₃
(c) H₂SO₄
(d) H₃PO₄
Answer: (c) H₂SO₄
5. When HCl is prepared by the reaction of NaCl with H₂SO₄, the property of H₂SO₄ exhibited is :
(a) Dehydrating agent (b) Drying agent
(c) Oxidising property (d) Non volatile acid
Answer: (d) Non volatile acid
6. The catalyst preferred in contact process is :
(a) Pt
(b) V₂O₅
(c) Fe
(d) Pd
Answer: (b) V₂O₅
7. The substance added to SO₃ to manufacture H₂SO₄ by contact process is :
(a) H₂O
(b) H₂SO₄
(c) H₂S₂O₇
(d) H₂S
Answer: (b) H₂SO₄
8. The role of sulphuric acid in the reaction given below is : S + 2H₂SO₄ → 3SO₂ + 2H₂O
(a) Non volatile acid
(b) Oxidising agent
(c) Dehydrating agent
(d) None of the above
Answer: (b) Oxidising agent
9. Dilute H₂SO₄ and conc. H₂SO₄ can be distinguished by:
(a) Copper
(b) Silver
(c) Gold
(d) Platinum
Answer: (a) Copper
10. On adding conc. H₂SO₄ to cane sugar, the colour observed is :
(a) yellow
(b) black
(c) green
(d) violet
Answer: (b) black
11. The acid which produces charcoal from sugar is :
(a) conc. HNO₃
(b) conc. HCl
(c) conc. H₂SO₄
(d) conc. H₃PO₄
Answer: (c) conc. H₂SO₄
12. The substance which can be used as a drying as well as dehydrating agent is :
(a) conc. H₂SO₄
(b) conc. HNO₃
(c) conc. HCl
(d) conc. H₂CO₃
Answer: (a) conc. H₂SO₄
13. The compound formed by the oxidation of sulphur by nitric acid is :
P Sulphuric acid Q Nitrogen dioxide
R Sulphur dioxide
(a) Only P
(b) Only Q
(c) Only R
(d) Both P and Q
Answer: (d) Both P and Q
14. Assertion (A): Sulphuric acid is known as the oil of vitriol.
Reason (R) : Sulphuric acid was first obtained by heating crystals of green vitriol.
1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.
(a) (1)
(b) (2)
(c) (3)
(d) (4)
Answer: (a) (1)
15. Assertion (A): V₂O₅ or Pt is used in the catalytic oxidation of sulphur dioxide.
Reason (R) : The catalytic oxidation of SO₂ is an exothermic reaction, so it requires to be heated to about 450°C only in the beginning.
1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.
(a) (1)
(b) (2)
(c) (3)
(d) (4)
Answer: (b) (2)
16. Assertion (A): Sulphuric acid when dissolved in water forms a basic salt.
Reason (R): Sulphuric acid ionises in two stages, it is a dibasic acid.
1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.
(a) (1)
(b) (2)
(c) (3)
(d) (4)
Answer: (d) (4)
17. Assertion (A): Pure sulphuric acid is almost a non-conductor of electricity.
Reason (R): Dilute sulphuric acid is a good conductor of electricity.
1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.
(a) (1)
(b) (2)
(c) (3)
(d) (4)
Answer: (b) (2)
18. Assertion (A): Impurity of arsenic oxide must be removed before passing the mixture of SO₂ and air through the catalytic chamber.
Reason (R): Arsenic oxide poisons the catalyst.
1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.
(a) (1)
(b) (2)
(c) (3)
(d) (4)
Answer: (a) (1)
19. Assertion (A): Concentrated sulphuric acid is kept in air tight bottles.
Reason (R): Air contains impurities, therefore H₂SO₄ will get spoiled.
1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.
(a) (1)
(b) (2)
(c) (3)
(d) (4)
Answer: (b) (2)
20. Assertion (A): Sulphuric acid acts as an oxidising agent.
Reason (R) : Sulphuric acid produces hydrogen on reacting with zinc.
1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.
(a) (1)
(b) (2)
(c) (3)
(d) (4)
Answer: (b) (2)
Very Short Answer Type
1. Following are the typical properties of dilute acid. Complete them by inserting suitable words :
(a) Active metal + acid → …………+ …………….
Answer: Active metal + acid → metallic sulphate + hydrogen.
(b) Base +Acid → ……………. + …………….
Answer: Base + Acid → salt + water.
(c) Carbonate/hydrogen carbonate + Acid → …………………+……………..+……………..
Answer: Carbonate/hydrogen carbonate + Acid → salt + water + carbon dioxide.
(d) Sulphite/hydrogen sulphite + Acid → ………………..+……………….+……………
Answer: Sulphite/hydrogen sulphite + Acid → salt + water + sulphur dioxide.
(e) Sulphide + Acid → ……………….. + ……………….
Answer: Sulphide + Acid → salt + hydrogen sulphide.
2. Name:
(a) The acid formed when sulphur dioxide dissolves in water.
Answer: The acid formed when sulphur dioxide dissolves in water is Sulphurous acid.
(b) The gas released when sodium carbonate is added to a solution of sulphur dioxide.
Answer: The gas released when sodium carbonate is added to a solution of sulphur dioxide is Carbon dioxide.
(c) Liquid E that can be dehydrated to produce ethene.
Answer: Liquid E that can be dehydrated to produce ethene is Ethyl alcohol (Ethanol).
(c) Liquid E that can be dehydrated to produce ethene.
Answer: Liquid E that can be dehydrated to produce ethene is Ethyl alcohol (Ethanol).
(d) The gas that can be oxidised to sulphur.
Answer: The gas that can be oxidised to sulphur is Hydrogen sulphide (H₂S).
(e) The solution which liberates sulphur dioxide gas from sodium sulphite.
Answer: The solution which liberates sulphur dioxide gas from sodium sulphite is Dilute sulphuric acid (H₂SO₄).
(e) The solution which liberates sulphur dioxide gas from sodium sulphite.
Answer: The solution which liberates sulphur dioxide gas from sodium sulphite is Dilute sulphuric acid (H₂SO₄).
(f) The gas produced on reaction of dilute sulphuric acid with a metallic sulphide.
Answer: The gas produced on reaction of dilute sulphuric acid with a metallic sulphide is Hydrogen sulphide (H₂S).
(g) A dilute mineral acid which forms a white precipitate when treated with barium chloride solution.
Answer: The dilute mineral acid which forms a white precipitate when treated with barium chloride solution is Dilute sulphuric acid (H₂SO₄).
(h) The acid which produces sugar charcoal from sugar.
Answer: The acid which produces sugar charcoal from sugar is Concentrated sulphuric acid (H₂SO₄).
(i) The acid on mixing with lead nitrate solution produces a white precipitate which is insoluble even on heating.
Answer: The acid on mixing with lead nitrate solution that produces a white precipitate which is insoluble even on heating is Sulphuric acid (H₂SO₄).
(a) The acid formed when sulphur dioxide dissolves in water.
Answer: The acid formed when sulphur dioxide dissolves in water is Sulphurous acid.
(b) The gas released when sodium carbonate is added to a solution of sulphur dioxide is Carbon dioxide.
(c) Liquid E that can be dehydrated to produce ethene is Ethyl alcohol.
(d) The gas that can be oxidised to sulphur is Hydrogen sulphide.
(e) The solution which liberates sulphur dioxide gas from sodium sulphite is dilute sulphuric acid.
(f) The gas produced on reaction of dilute sulphuric acid with a metallic sulphide is Hydrogen sulphide.
(g) A dilute mineral acid which forms a white precipitate when treated with barium chloride solution is dilute sulphuric acid.
(h) The acid which produces sugar charcoal from sugar is concentrated sulphuric acid.
(i) The acid on mixing with lead nitrate solution that produces a white precipitate which is insoluble even on heating is sulphuric acid.
3. What is the name given to the salts of : (a) sulphurous acid, (b) sulphuric acid ?
Answer: (a) The salts of sulphurous acid are called sulphites.
(b) The salts of sulphuric acid are called sulphates.
4. What property of conc. H₂SO₄:
(a) is used in the action when sugar turns black in its presence.
(b) allows it to be used in the preparation of HCl and HNO₃ acids.
Answer: (a) The property of conc. H₂SO₄ used in the action when sugar turns black in its presence is its dehydrating agent property.
(b) The property of conc. H₂SO₄ that allows it to be used in the preparation of HCl and HNO₃ acids is its non-volatile nature.
5. State the property of sulphuric acid shown by the reaction of conc. sulphuric acid when heated with
(a) potassium nitrate
(b) carbon
(c) ethanol
Answer: The property of sulphuric acid shown by the reaction of conc. sulphuric acid when heated with:
(a) potassium nitrate is its non-volatile nature.
(b) carbon is its oxidising agent property.
(c) ethanol is its dehydrating agent property.
6. Some properties of Sulphuric acid are listed below. Choose the property A, B, C or D which is responsible for the reactions (i) to (iv). Some properties may be repeated:
A. Typical acid
B. Dehydrating agent
C. Non-volatile acid
D. Oxidizing agent
(i) C₁₂H₂₂O₁₁ + nH₂SO₄ → 12C + 11H₂O + nH₂SO₄
(ii) NaCl + H₂SO₄ → NaHSO₄ + HCl
(iii) CuO + H₂SO₄ → CuSO₄ + H₂O
(iv) Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂
Answer: The property responsible for the reactions is:
(i) For C₁₂H₂₂O₁₁ + nH₂SO₄ → 12C + 11H₂O + nH₂SO₄, the property is B. Dehydrating agent.
(ii) For NaCl + H₂SO₄ → NaHSO₄ + HCl, the property is C. Non-volatile acid.
(iii) For CuO + H₂SO₄ → CuSO₄ + H₂O, the property is A. Typical acid.
(iv) For Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂, the property is A. Typical acid.
7. Some properties of sulphuric acid are listed below. Choose the role played by sulphuric acid as A, B, C or D which is responsible for the reactions (i) to (v). Some role/s may be repeated.
(A) Dilute acid
(B) Dehydrating agent
(C) Non-volatile acid
(D) Oxidising agent
(a) CuSO₄.5H₂O –conc. H₂SO₄–> CuSO₄ + 5H₂O
(b) S + 2H₂SO₄ [conc.] → 3SO₂ + 2H₂O
(c) NaNO₃ + H₂SO₄ [conc.] <200°C→ NaHSO₄ + HNO₃
(d) MgO + H₂SO₄ → MgSO₄ + H₂O
(e) Zn + 2H₂SO₄ [conc.] → ZnSO₄ + SO₂ + 2H₂O
Answer: The role played by sulphuric acid in the reactions is:
(a) In CuSO₄.5H₂O –conc. H₂SO₄–> CuSO₄ + 5H₂O, sulphuric acid acts as a (B) Dehydrating agent.
(b) In S + 2H₂SO₄ [conc.] → 3SO₂ + 2H₂O, sulphuric acid acts as an (D) Oxidising agent.
(c) In NaNO₃ + H₂SO₄ [conc.] <200°C→ NaHSO₄ + HNO₃, sulphuric acid acts as a (C) Non-volatile acid.
(d) In MgO + H₂SO₄ → MgSO₄ + H₂O, sulphuric acid acts as a (A) Dilute acid (displaying typical acid property).
(e) In Zn + 2H₂SO₄ [conc.] → ZnSO₄ + SO₂ + 2H₂O, sulphuric acid acts as an (D) Oxidising agent.
8. Copy and complete the following table relating to an important industrial process and its final output.
Answer: The completed table is as follows:
9. Copy and complete the following table :
Answer: The completed table is as follows:
Short Answer Type
1. Give reasons for the following:
(a) Sulphuric acid forms two types of salts with NaOH,
Answers: Sulphuric acid forms two types of salts with NaOH because sulphuric acid is a dibasic acid. It ionises in two stages.
(b) A piece of wood becomes black when concentrated sulphuric acidispoured on it,
Answers: A piece of wood becomes black when concentrated sulphuric acid is poured on it because concentrated sulphuric acid is a powerful dehydrating agent. Cellulose, a component of wood, is a carbohydrate, and when it reacts with concentrated sulphuric acid, it is dehydrated to a black spongy mass of carbon. The wood is said to get charred.
(c) Brisk effervescence is seen when oil of vitriol is added to sodium carbonate.
Answer: Brisk effervescence is seen when oil of vitriol (sulphuric acid) is added to sodium carbonate because sulphuric acid liberates carbon dioxide from metallic carbonates. The reaction is: Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂↑. The evolution of carbon dioxide gas causes the brisk effervescence.
2. Why is water not added to concentrated H₂SO₄ in order to dilute it?
Answer: Water is never poured on acid to dilute it as a large amount of heat is evolved which changes poured water to steam. The steam so formed causes spurting of acid which can cause burn injuries. Therefore, dilution is done by pouring acid on a given amount of water in a controlled manner by continuous stirring; otherwise, acid being heavier will settle down. The evolved heat is dissipated in the water itself and hence the spurting of the acid is minimized.
3. Why is:
(a) concentrated sulphuric acid kept in air tight bottles?
Answer: (a) Concentrated sulphuric acid is kept in air tight bottles because it is a dense, oily, hygroscopic liquid. It absorbs moisture from the air, so H₂SO₄ should always be kept stoppered to prevent it from absorbing atmospheric moisture and becoming diluted.
(b) H₂SO₄ is not used as a drying agent for H₂S?
Answers: H₂SO₄ is not used as a drying agent for H₂S because concentrated sulphuric acid reacts with hydrogen sulphide. The reaction is: H₂S + H₂SO₄ (conc.) → S + 2H₂O + SO₂↑. Since it reacts with H₂S, it cannot be used to dry it.
(c) Sulphuric acid used in the preparation of HCI and HNO₃? Give equations in both cases.
Answers: Sulphuric acid is used in the preparation of HCl and HNO₃ because concentrated sulphuric acid has a high boiling point (338°C) and so, it is considered to be a non-volatile acid. It is, therefore, used for preparing volatile acids like hydrochloric acid and nitric acid from their salts by double decomposition.
The equations are:
For HCl: NaCl + H₂SO₄ (conc.) → NaHSO₄ + HCl
For HNO₃: NaNO₃ + H₂SO₄ (conc.) → NaHSO₄ + HNO₃
State your observation when –
(a) Sugar crystals are added to a hard glass test tube containing conc. sulphuric aicd.
Answer: When sugar crystals are added to a hard glass test tube containing conc. sulphuric acid, the sugar reacts immediately to give a black spongy mass of carbon which rises up. Steam is given off and the whole mass gets heated due to an exothermic reaction. The sugar is said to get charred.
(b) Conc. H₂SO₄ is added to a crystal of hydrated copper sulphate.
Answers: When conc. H₂SO₄ is added to a crystal of hydrated copper sulphate (CuSO₄.5H₂O), which is blue, it becomes white (anhydrous copper sulphate). This is because conc. sulphuric acid removes the water of crystallisation from the salt.
5. Give balanced equation(s) for :
(a) Reaction of dilute sulphuric acid when poured over sodium sulphite.
Answer: Reaction of dilute sulphuric acid when poured over sodium sulphite:
Na₂SO₃ + H₂SO₄ (dil) → Na₂SO₄ + H₂O + SO₂↑
(b) Manufacture of sulphuric acid by the contact process.
Answer: The main reactions are:
1. S + O₂ → SO₂ (or 4FeS₂ + 11O₂ → 2Fe₂O₃ + 8SO₂)
2. 2SO₂ + O₂ ⇌ (V₂O₅/Pt catalyst, 400-450°C) 2SO₃
3. SO₃ + H₂SO₄ → H₂S₂O₇ (oleum)
4. H₂S₂O₇ + H₂O → 2H₂SO₄
(c) Heating sulphur with conc. sulphuric acid.
Answer: Heating sulphur with conc. sulphuric acid:
S + 2H₂SO₄ (conc.) → 3SO₂ + 2H₂O
(d) Dehydration of sugar crystals by concentrated sulphuric acid.
Answer: Dehydration of sugar crystals by concentrated sulphuric acid:
C₁₂H₂₂O₁₁ (s) (Cane Sugar) + Conc. H₂SO₄ → 12C(s) + 11H₂O
(e) Action of concentrated sulphuric acid on carbon.
Answer: Action of concentrated sulphuric acid on carbon:
C + 2H₂SO₄ (conc.) → CO₂ + 2H₂O + 2SO₂↑
6. Write the equations for the following reactions :
(a) dil. H₂SO₄ and barium chloride:
Answer: BaCl₂ + H₂SO₄ → BaSO₄↓ + 2HCl
(b) dil. H₂SO₄ and sodium sulphide:
Answer: Na₂S + H₂SO₄ (dil) → Na₂SO₄ + H₂S↑
(c) Zinc sulphide and dilute sulphuric acid:
Answer: ZnS + H₂SO₄ (dil) → ZnSO₄ + H₂S↑
7. Dilute and concentrated sulphuric acid can be distinguished by using metals copper and zinc. Explain by giving balanced equations.
Answer: Dilute and concentrated sulphuric acid can be distinguished using copper and zinc as follows:
- With Zinc (Zn):
- Dilute H₂SO₄: Zinc reacts with dilute sulphuric acid to produce hydrogen gas.
Zn + H₂SO₄ (dil) → ZnSO₄ + H₂↑ - Concentrated H₂SO₄: Zinc reacts with concentrated sulphuric acid to produce sulphur dioxide gas, not hydrogen.
Zn + 2H₂SO₄ (conc.) → ZnSO₄ + 2H₂O + SO₂↑
- Dilute H₂SO₄: Zinc reacts with dilute sulphuric acid to produce hydrogen gas.
- With Copper (Cu):
- Dilute H₂SO₄: Copper does not react with dilute sulphuric acid as it is below hydrogen in the activity series.
Cu + H₂SO₄ (dil) → No reaction - Concentrated H₂SO₄: Copper reacts with hot concentrated sulphuric acid to produce sulphur dioxide gas.
Cu + 2H₂SO₄ (conc.) → CuSO₄ + 2H₂O + SO₂↑
- Dilute H₂SO₄: Copper does not react with dilute sulphuric acid as it is below hydrogen in the activity series.
Thus, zinc produces different gases with dilute and concentrated H₂SO₄. Copper reacts only with concentrated H₂SO₄, producing SO₂ gas, and shows no reaction with dilute H₂SO₄. The evolution of pungent SO₂ gas (which can turn acidified potassium dichromate solution green) is characteristic of reactions with concentrated sulphuric acid.
8. Give two balanced reactions of each type to show the following properties of sulphuric acid :
(a) Acidic nature:
Answer: 1. Reaction with an active metal:
Mg + H₂SO₄ (dil) → MgSO₄ + H₂↑
2. Neutralisation of a base (metal oxide):
CuO + H₂SO₄ (dil.) → CuSO₄ + H₂O
(b) Oxidising agent (reactions with conc. H₂SO₄):
Answer:1. Oxidation of a non-metal (carbon):
C + 2H₂SO₄ (conc.) → CO₂ + 2H₂O + 2SO₂↑
2. Oxidation of a metal (copper):
Cu + 2H₂SO₄ (conc.) → CuSO₄ + 2H₂O + SO₂↑
(c) Dehydrating nature (reactions with conc. H₂SO₄):
Answer: 1. Dehydration of hydrated copper (II) sulphate:
CuSO₄.5H₂O + Conc. H₂SO₄ → CuSO₄(s) + 5H₂O
2. Dehydration of cane sugar:
C₁₂H₂₂O₁₁ (s) + Conc. H₂SO₄ → 12C(s) + 11H₂O
(d) Non-volatile nature (reactions with conc. H₂SO₄):
Answer: 1. Preparation of hydrochloric acid:
NaCl + H₂SO₄ (conc.) → NaHSO₄ + HCl
2. Preparation of nitric acid:
NaNO₃ + H₂SO₄ (conc.) → NaHSO₄ + HNO₃
9. Give a chemical test to distinguish between :
(a) Dilute sulphuric acid and dilute hydrochloric acid, (using lead nitrate solution):
Answer: Add lead nitrate solution to both acids.
Dilute sulphuric acid: Forms a white precipitate of lead sulphate (PbSO₄) which is insoluble even on heating.
Pb(NO₃)₂ + H₂SO₄ (dil) → PbSO₄↓ + 2HNO₃
Dilute hydrochloric acid: May form a white precipitate of lead chloride (PbCl₂), especially if the solution is concentrated. However, lead chloride is soluble in hot water. If a precipitate forms, it will dissolve on heating, unlike lead sulphate.
Pb(NO₃)₂ + 2HCl (dil) → PbCl₂↓ + 2HNO₃ (precipitate soluble in hot water)
(b) Dilute sulphuric acid and conc. sulphuric acid:
Answer: Add copper turnings to both acids and warm if necessary.
Dilute sulphuric acid: No reaction occurs with copper.
Concentrated sulphuric acid: Reacts with copper to evolve sulphur dioxide gas, which has a pungent smell and turns acidified potassium dichromate paper green.
Cu + 2H₂SO₄ (conc.) → CuSO₄ + 2H₂O + SO₂↑
(c) Dilute sulphuric acid and dilute hydrochloric acid [using barium chloride solution]:
Answer: Add barium chloride solution to both acids.
Dilute sulphuric acid: Forms a white precipitate of barium sulphate (BaSO₄), which is insoluble in dilute hydrochloric acid or nitric acid.
BaCl₂ + H₂SO₄ (dil) → BaSO₄↓ + 2HCl
Dilute hydrochloric acid: No precipitate is formed with barium chloride solution.
10. State the conditions required for the conversion of sulphur dioxide to sulphur trioxide to take place.
Answer: The conditions required for the conversion of sulphur dioxide (SO₂) to sulphur trioxide (SO₃) in the Contact process are:
(i) Temperature: The temperature should be as low as possible, as the reaction is exothermic. The optimum yield is found at about 410-450°C.
(ii) Pressure: High pressure favours the reaction, but acid-resistant towers are difficult to build. Hence a pressure of 1 – 2 atmospheres is used.
(iii) Catalyst: A suitable catalyst is used, typically vanadium pentoxide (V₂O₅). Platinum (Pt) can also be used but is more expensive and easily poisoned.
(iv) Excess of oxygen: An excess of oxygen increases the production of sulphur trioxide.
11. Making use only of substances given : dil. sulphuric acid, sodium carbonate, zinc, sodium sulphite, lead, calcium carbonate: Give equations for the reactions by which you could obtain:
Answer: (a) Hydrogen:
Zn + H₂SO₄ (dil) → ZnSO₄ + H₂↑
(b) Sulphur dioxide:
Na₂SO₃ + H₂SO₄ (dil) → Na₂SO₄ + H₂O + SO₂↑
(c) Carbon dioxide:
Na₂CO₃ + H₂SO₄ (dil) → Na₂SO₄ + H₂O + CO₂↑
(or CaCO₃ + H₂SO₄ (dil) → CaSO₄ + H₂O + CO₂↑)
(d) Zinc carbonate [2 steps]:
Step 1: Formation of zinc sulphate solution.
Zn + H₂SO₄ (dil) → ZnSO₄ + H₂
Step 2: Precipitation of zinc carbonate using sodium carbonate solution.
ZnSO₄ + Na₂CO₃ → ZnCO₃↓ + Na₂SO₄
12. Give equations for the action of sulphuric acid on
(a) Potassium hydrogen carbonate (assuming dilute sulphuric acid):
Answer: 2KHCO₃ + H₂SO₄ (dil) → K₂SO₄ + 2H₂O + 2CO₂↑
(b) Sulphur (assuming concentrated sulphuric acid):
Answer: S + 2H₂SO₄ (conc.) → 3SO₂ + 2H₂O
13. In the manufacture of sulphuric acid by contact process give the equations for the conversion of sulphur trioxide to sulphuric acid.
Answer: The conversion of sulphur trioxide (SO₃) to sulphuric acid (H₂SO₄) in the Contact process involves two steps:
- Absorption of sulphur trioxide in concentrated sulphuric acid to form oleum (pyrosulphuric acid):
SO₃ + H₂SO₄ (conc.) → H₂S₂O₇ - Dilution of oleum with water to obtain sulphuric acid of the desired strength:
H₂S₂O₇ + H₂O → 2H₂SO₄
14. Give a balanced equation for the conversion of zinc oxide to zinc sulphate.
Answer: ZnO + H₂SO₄ (dil) → ZnSO₄ + H₂O
Long Answer Type
1. What property of conc. H2SO4 is made use of in each of the following cases? Give an equation for the reaction in each case:
Answer: (a) In the production of HCl gas when it reacts with a chloride, the non-volatile nature of concentrated sulphuric acid is made use of. Concentrated sulphuric acid has a high boiling point and is used for preparing volatile acids like hydrochloric acid from their salts by double decomposition.
The equation for the reaction is:
NaCl + H2SO4 (conc.) → NaHSO4 + HCl
(b) In the preparation of CO from HCOOH, the dehydrating property of concentrated sulphuric acid is used.
The equation for the reaction is:
HCOOH –Conc. H2SO4–> CO + H2O
(Formic acid)
(c) As a source of hydrogen by diluting it and adding a strip of magnesium, the acidic property of dilute sulphuric acid is used. Dilute sulphuric acid reacts with metals, which are above hydrogen in the activity series to form metallic sulphate and hydrogen.
The equation for the reaction is:
Mg + H2SO4 (dil) → MgSO4 + H2↑
(d) In the preparation of sulphur dioxide by warming a mixture of conc. sulphuric acid and copper-turnings, the oxidising property of concentrated sulphuric acid is used. On thermal decomposition, it yields nascent oxygen [O], which oxidises metals.
The equation for the reaction is:
Cu + 2H2SO4 (conc.) → CuSO4 + 2H2O + SO2 ↑
(e) When hydrogen chloride gas is passed through concentrated sulphuric acid, its property as a drying agent is made use of. Concentrated sulphuric acid is used to dry gases like HCl gas.
(f) Its reaction with:
(i) Ethanol: The dehydrating property of concentrated H2SO4 is used. Organic compounds like ethyl alcohol are dehydrated by conc. H2SO4.
The equation for the reaction is:
C2H5OH –Conc. H2SO4, 170°C–> C2H4 + H2O
(Ethyl alcohol) (Ethylene)
(ii) Carbon: The oxidising property of concentrated sulphuric acid is used. Nascent oxygen from the thermal decomposition of H2SO4 oxidises non-metals like carbon.
The equation for the reaction is:
C + 2H2SO4 (conc.) → CO2 + 2H2O + 2SO2↑
2. (a) Which property of sulphuric acid accounts for its use as a dehydrating agent?
Answer: The property of sulphuric acid that accounts for its use as a dehydrating agent is its great affinity for water. It readily removes chemically combined water molecules, i.e., elements of water from other compounds, thus it acts as a dehydrating agent.
(b) Concentrated sulphuric acid is both an oxidizing agent and a non-volatile acid. Write one equation each to illustrate the above mentioned properties of sulphuric acid.
Answer: To illustrate the oxidizing agent property of concentrated sulphuric acid, an equation is:
C + 2H2SO4 (conc.) → CO2 + 2H2O + 2SO2↑
To illustrate the non-volatile acid property of concentrated sulphuric acid, an equation is:
NaCl + H2SO4 (conc.) → NaHSO4 + HCl
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