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Sulphurdioxide, Sulphuric acid and
Hydrogen sulphide (Solved)
Question .1. (i) Give equations for the following conversions:
(a) Sulphur dioxide to Sulphur
(b) Sulphur dioxide to sodium sulphite
(c) sodium sulphite to Sulphur dioxide.
(ii) (a)Write the equation for the laboratory preparation of Sulphur dioxide from sodium sulphite.
(b) How is the SO2 collected?
(c) What does the method of collection tell you about the density of SO2?
(d) What do you see when SO2 is bubbled through an acidified K2Cr2O7 solution?
(iii) Write one equation in each case to show the action of Sulphur dioxide as:
(a) a reducing agent
(b) an oxidizing agent
(c) an acid anhydride.
(iv) When burning Sulphur [i.e. SO2] reacts with H2O, a compound is formed. Name the compound.
(v) Give the balanced equation for reaction between SO 2 and moist Cl2.
(vi) Write a balanced equation for: SO2 and sodium hydroxide solution. [formation of normal salt].
(vii) What type of substance will liberate Sulphur dioxide from sodium sulphite.
(viii) Write the equation for the reaction by which Sulphur dioxide is converted into sodium
sulphite.
Answer :
(i) (a) 2Mg [heated] + SO2 → 2MgO + S.
(b) 2NaOH SO2 → Na2SO3 + H2O.
(c) Na2SO3 + H2SO4 → Na2SO4 + H2O + SO2
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Na2SO3 + 2HCl → 2NaCl + H2O + SO2.
(ii) (a) Na2SO3 + 2HCl → 2NaCl + H2O + SO2.
(b) Sulphur dioxide is collected by upward displacement of air.
(c) Sulphur dioxide is 2.2 times heavier than air.
(d) When SO2 is bubbled through acidified solution of K2Cr2O7, the orange colour of potassium dichromate solution
turns to clear green due to formation of chromium sulphate:
K2Cr2O7 + H2SO4 + 3SO2 → Cr2(SO4)2 + H2O.
(iii) (a) 2HNO3 + SO2 → 2NO2 + H2SO4.
(b) 2Mg [heated] + SO2 → 2MgO + S.
(c) H2O + SO2 → H2SO3.
(iv) sulphurous acid.
(v) SO2 + Cl2 + 2H2O → 2HCl + H2SO4.
(vi) 2NaOH + SO2 → Na2SO3 + H2O.
(vii) Any mineral acid HCl, H2SO4 or HNO3.
(viii) Na2O + SO2 → Na2SO3.
Question .2. (i) Give one similarity and two differences between bleaching action of SO2 gas and
chlorine gas.
(ii) From the following gases – ammonia, chlorine, hydrogen chloride, Sulphur dioxide, select the
gas that matches the description given below and answer the questions that follow: Gas A is a
reducing agent which contains oxygen.
(a) What is the name of the gas A?
(b) What would you observe if gas A is bubbled through acidified potassium dichromate solution.
(iii) Write the observations and balanced equations for the reaction: A paper dipped in potassium
permanganate solution is put on the mouth of a test-tube containing Sulphur dioxide gas.
(iv) From the gases – ammonia, hydrogen chloride, hydrogen sulphide, Sulphur dioxide – select
the following:
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(a) This gas can be oxidized to Sulphur.
(b) This gas decolourises potassium permanganate solution.
(c) This gas can be obtained by the reaction between copper and concentrated sulphuric acid.
(v) The bleaching action of Cl 2 is permanent whereas the bleaching action of SO2 is temporary.
(a) Give a reason why chlorine is not used to bleach silk.
(b) State the similarity in the use of Sulphur dioxide and chlorine as bleaching agent.
(c) Explain the bleaching action of Sulphur dioxide with the help of chemical equations.
(d) Why is bleaching by Sulphur dioxide only temporary.
(vi) State what is observed when Sulphur dioxide is passed through a jar containing bromine
water.
(vii) Give a reason why Sulphur dioxide is used as an antichlor.
Answer :
(i)
Chlorine
Sulphur dioxide
Similarity : Presence of moisture
is essential for bleaching.
Cl2 + H2O → HCl + HOCl
SO2 + 2H2O → H2SO4+ [H]
Dissimilarity
1. Bleaches by oxidation.
1. Bleaches by reduction.
2. Bleaching is permanent.
2. Bleaching is temporary.
3. Strong bleaching agent.
3. Mild bleaching agent.
(ii) (a) Sulphur dioxide. (b) Orange coloured acidified potassium dichromate solution changes to green.
(iii) Pink colour of paper is disappeared.
2KMnO4 + 2H2O + 5SO2 → 2MnSO4 + K2SO4 + 2H2SO4.
(iv) (a) Hydrogen sulphide. (b) Sulphur dioxide. (c) Sulphur dioxide.
(v) (a) Chlorine damages the silk.
(b) Both act as bleaching agents in presence of moisture.
(c) SO2 (g) + 2H2O → H2SO4 (aq.) + 2[H]
2[H] + colouring matter → Colourless matter.
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(d) Because oxygen present in air oxidizes the reduced dye.
(vi) Red colour of bromine water disappears.
(vii) Sulphur dioxide acts as a reducing agent, reduces halogens to hydrogen halides.
SO2 + 2H2O + Cl2 → 2HCl + H2SO4.
Question .3. (i) Name the oxide of Sulphur which reacts with water to give sulphuric acid.
(ii) In the Contact Process, the direct reaction between oxide of Sulphur and water is avoided. In
this process, what does the oxide of Sulphur react with instead of water and what is the name of
the product?
(iii) (a) What is the purpose of the Contact Process.
(b) Name the catalyst used in the Contact Process.
(c) Write the balanced equation for the reaction in the process which takes place in the presence
of catalyst.
(iv) (a) Name the catalyst used industrially which speeds up the conversion of SO 2 and SO3in the
production of sulphuric acid in the laboratory or industrially.
(b) Write the equation for the conversion of Sulphur dioxide to Sulphur trioxide. Why does this
reaction supply energy.
(c) What is the name of the compound formed between SO 3 and sulphuric acid.
(v) State the name of the process by which H2SO4 is manufactured. Name the catalyst used.
(vi) Name the catalyst which helps in the conversion of Sulphur dioxide to Sulphur trioxide.
(vii) 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-step procedure is used. Write
the equations for the two steps involved.
(viii) Name the process used for the large scale manufacture of sulphuric acid.
Answer : (i) Sulphur trioxide.
(ii) Concentrated sulphuric acid. Oleum or Pyrosulphuric acid.
(iii) (a) To manufacture sulphuric acid.
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(b) Vanadium pentaoxide or platinised asbestos.
(c)
V2O2
2SO2 + O2 → 2SO3
450ºC
(iv) (a) Vanadium pentaoxide or platinised asbestos.
(b)
V2O2
2SO2 + O2 → 2SO3
450ºC
The reaction supplies energy as the reaction is exothermic in nature.
(c) Oleum or Pyrosulphuric acid.
(v) H2SO4 is manufactured by Contact Process. The catalyst used in the process is Vanadium pentaoxide or
Platinised asbestos.
(vi) Vanadium pentaoxide or Platinised asbestos.
(vii) SO3 + H2SO4 → H2S2O7 (Oleum).
H2S2O7 + H2O → 2H2SO4.
(viii) Contact Process.
Question .4. (i) Write correctly balanced equation for the reaction between Iron and dilute
sulphuric acid.
(ii) Write correctly balanced equations for the reaction of dilute sulphuric acid with each of the
following: (a) Copper carbonate
(b) Lead nitrate solution
(c) Zinc hydroxide.
(iii) Write a balanced equation for the reaction between zinc and dilute sulphuric acid.
(iv) Write equation for: (a) Dilute H2SO4 – producing H2.
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(b) Between Pb(NO3)2 solution and dil. H2SO4.
(v) State the substance/s reacted with dilute or concentrated sulphuric acid to form the following
gases:
(a) Hydrogen (b) Carbon dioxide.
State whether the acid used in each case is dilute or concentrated.
(vi) Write the equation for the laboratory preparation of:
(a) Sodium sulphate using dilute sulphuric acid.
(b) Lead sulphate using dilute sulphuric acid.
(vii) Write balanced equation for the reaction between
(a) Potassium hydrogen carbonate and dilute sulphuric acid.
(b) Sodium nitrate and concentrate sulphuric acid.
(viii) What do you see when concentrated sulphuric acid is added to copper sulphate-5-water.
(ix) “Concentrated sulphuric acid is used in the laboratory preparation of nitric acid and
hydrochloric acid because it is ________ [less volatile / stronger] in comparison to these two
acids.”
(x) Write the equations for the laboratory preparation of the following salts using sulphuric acid.
(a) Copper sulphate from copper.
(b) Lead sulphate from lead nitrate.
(xi) Choose the property of sulphuric acid (A, B, C or D), which is relevant to each of the
preparations [a] to [c] : A: Dil. acid (typical acid properties), B: Non-volatile acid, C: Oxidizing agent, D: Dehydrating
agent.
(a) Preparation of hydrogen chloride.
(b) Preparation of ethane from ethanol.
(c) Preparation of copper sulphate from copper oxide.
(xii) Which property of sulphuric acid accounts for its use as a dehydrating agent.
(xiii) 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.
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Answer : (i) Fe + H2SO4 (dil.) → FeSO4 + H2.
(ii) (a) CuCO3 + H2SO4 (dil.) → CuSO4 + H2O + CO2.
(b) Pb(NO3)2 + H2SO4 (dil.) → PbSO4 ↓ + 2HNO3.
(c) Zn(OH)2 + H2SO4 (dil.) → ZnSO4 + 2H2O.
(iii) Zn + H2SO4 (dil.) → ZnSO4 + H2.
(iv) (a) Zn + H2SO4 (dil.) → ZnSO4 + H2.
(b) Pb(NO3)2 + H2SO4 (dil.) → PbSO4 ↓ + 2HNO3.
(v) (a) Active metals like Zn or Fe with dilute sulphuric acid.
(b) Carbonates or bicarbonates of metals with dilute sulphuric acid.
(vi) (a) Na2O + H2SO4 (dil.) → Na2SO4 + H2O.
2NaOH + H2SO4 (dil.) → Na2SO4 + 2H2O.
Na2SO3 + H2SO4 (dil.) → Na2SO4 + H2O + SO2.
2NaHSO3 + H2SO4 (dil.) → Na2SO4 + 2H2SO4 + 2SO2.
(b) Pb(NO3)2 + H2SO4 (dil.) → 2HNO3 + PbSO4 ↓
(vii) (a) 2KHCO3 + H2SO4 (dil.) → K2SO4 + 2H2O + 2CO2.
(b) NaNO3 + H2SO4 (conc.) → NaHSO4 + HNO3 (vap.)
(viii)
H2SO4
CuSO4.5H2O → CuSO4 + 5H2O.
[blue hydrous] [conc.] [white anhydrous]
(ix) Less volatile.
(x) (a) Cu + 2H2SO4 (conc.) → CuSO4 + 2H2O + SO2.
(b) Pb(NO3)2 + H2SO4 → 2HNO3 + PbSO4 ↓.
(xi) (a) B (non-volatile acid). (b) D (dehydrating agent). (c) A (dilute acid).
(xii) Sulphuric acid’s high affinity for water accounts for its use as a dehydrating agent.
(xiii) Oxidizing agent :
S + 2H2SO4 (conc.) → 3SO2 + 2H2O.
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Non volatile acid :
2NaNO3 + H2SO4 (conc.) → Na2SO4 + 2HNO3.
Question .5. (i) What do you observe when barium chloride solution is added to dilute sulphuric
acid.
(ii) Supply the word (or words) that will make the sentence into a correct statement and rewrite the
sentence. Copper sulphate crystals are dehydrated by sulphuric acid.
(iii) Explain how a reagent chosen from : - ammonium hydroxide, barium chloride, sodium
chloride, sodium hydroxide, sulphuric acid and nitric acidenables to distinguish between the two
acids mentioned therein.
Answer : (i) A white precipitate of barium sulphate is formed which is insoluble in all mineral acids.
(ii) Blue hydrous copper sulphate turns into white anhydrous copper sulphate due to removal of water of
crystallization by concentrated sulphuric acid.
(iii) With BaCl2 solution, sulphuric acid will give white precipitate while nitric acid will not give any precipitate.
Question .6. (i) When H2S reacts with oxidizing agents, what substance is always a product of the
reaction.
(ii) State the colour of the precipitate formed when H2S is bubbled through copper sulphate
solution.
(iii) State how you can obtain H2S from iron (II) sulphide.
(iv) Name a gas which smells of rotten eggs.
(v) What is observed when hydrogen sulphide gas is passed through lead acetate solution.
(vi) Select the correct compound from the list given – Ammonia, Copper oxide, Copper sulphate,
Hydrogen chloride, Hydrogen sulphide, Lead bromide – which matches the description given
below: The compounds smells of rotten eggs.
Answer : (i) Sulphur.
(ii) Black precipitate of CuS.
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CuSO4 + H2S → CuS ↓ + H2SO4.
(iii) Hydrogen sulphide is obtained by the action of dilute H2SO4 on iron (II) sulphide.
(iv) Hydrogen sulphide.
(v) When hydrogen sulphide gas is passed through lead acetate solution, black coloured precipitate of lead sulphide
is formed.
Pb(CH3COO)2 + H2S → PbS ↓ + 2CH3COOH.
(vi) Hydrogen sulphide.