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Chemistry - Nitric Acid (Solved)
Question .1. Write a balanced equation for the reaction of nitrogen monoxide and oxygen.
Answer : 2NO + O2 → 2NO2.
Question .2. (i) Write the equation for the preparation of nitric acid from potassium nitrate.
(ii) What compounds are required for the laboratory preparation of nitric acid?
(iii) Choose the correct word from the brackets to complete the sentence. Sodium nitrate reacts
with _______ [concentrated / dilute] sulphuric acid to produce nitric acid. Write equation for the
same.
Answer : (i) <200ºC
KNO3 + H2SO4 (conc.) → KHSO4 + HNO3
(ii) (a) Concentrated sulphuric acid and
(b) Nitre or Chile salt petre.
(iii) Concentrated.
NaNO3 + H2SO4 (conc.) → NaHSO4 + HNO3.
Question .3. (i) When nitric acid is prepared by the action of concentrated sulphuric acid on
potassium nitrate, what is the special feature of the apparatus used?
(ii) Explain why only all-glass apparatus should be used for the preparation of nitric acid by
heating concentrated sulphuric acid and potassium nitrate.
Answer : (i) All-glass apparatus is used. Long neck of glass retort is inserted into the neck of receiver which is being
cooled from outside.
(ii) Nitric acid is highly corrosive and therefore destroys rubber and cork of the apparatus.
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Question .4. The first step in the manufacture of HNO 3 is the catalytic oxidation of NH3 . Name the
catalyst used.
Answer : Platinum.
Question .5. (i) State why pure nitric acid takes on a yellowish brown colour when exposed to
light.
(ii) Account for the yellow colour that appears in concentrated nitric acid when it is left standing
in an ordinary glass bottle.
(iii) State what is observed when nitric acid is kept in a reagent bottle for a long time.
Answer : (i) Nitric acid takes yellowish brown colour due to the presence of dissolved nitrogen dioxide.
(ii) Nitric acid slowly decomposes even at room temperature, specially in the presence of sunlight.
4HNO3 → 4NO2 + 2H2O + O2.
Liberated nitrogen dioxide dissolves in the acid and gives a yellow colour.
(iii) Brown vapours are seen in the bottle and the nitric acid turns yellowish in colour.
Question .6. (i) State the conc. acid which will oxidize Sulphur directly to H 2SO4. Write the
equation for the same.
(ii) Write a balanced equation for the reaction of Sulphur and hot concentrated nitric acid.
(iii) Dilute nitric acid is generally considered a typical acid except for its reaction with metals. In
what way is dilute nitric acid different from other acids when it reacts with metals.
Answer : (i) Hot and conc. nitric acid.
S + 6HNO3 (Hot & Conc.) → H2SO4 + 2H2O + 6NO2.
(ii) S + 6HNO3 (Hot & Conc.) → H2SO4 + 2H2O + 6NO2.
(iii) It acts as an oxidizing agent so hydrogen gas is not liberated. Instead NO gas and water are formed.
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Question .7. (i) Write the equations for the reaction between copper and concentrated nitric acid.
(ii) Name a solution which gives nitrogen dioxide with copper.
(iii) Write a balanced for the reaction of conc. HNO 3 when added to copper turnings kept in a
beaker.
(iv) Write the equation for the reaction of dilute nitric acid with copper.
Answer : (i) Cu + 4HNO3 (Conc.) → Cu(NO3)2 + 2H2O + 2NO2.
(ii) Nitric acid.
(iii) Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2.
(iv) 3Cu + 8HNO3 → 3Cu(NO3)2 + 4H2O + 2NO.
Question .8. (i) Describe what you see [observe] when concentrated nitric acid is added to copper.
(ii) Potassium nitrate is produced from KOH and nitric acid. State the type of reaction involved.
Answer : (i) Pinkish red metal dissolves in nitric acid to give blue coloured solution of copper nitrate and a reddish
brown coloured gas of NO2
volves which turns freshly prepared acidified ferrous sulphate solution brown black.
Δ
Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2.
(ii) Neutralization reaction.
Question .9. (i) Name a nitrate which on heating gives oxygen as the only gaseous product.
(ii) Write an equation for the following reaction: Action of heat on:
(a) potassium nitrate and
(b) sodium nitrate.
(iii) Name a gas that you can obtain in the laboratory from ammonium nitrate and write the
equation for the reaction taking place to obtain the gas.
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(iv) Give the name of soluble lead salt and write the equation for the action of heat on this salt.
(v) Write correctly balanced equation for the reaction of nitrogen and oxygen when lightning
strikes.
(vi) From the following substances, choose one in each case which matches the description given
below:
Ammonium nitrate, calcium hydrogen carbonate, copper carbonate, lead carbonate, lead nitrate,
potassium nitrate, sodium carbonate, sodium hydrogen carbonate, zinc carbonate.
(a) A nitrate which gives off only oxygen when heated.
(b) A nitrate which on heating decomposes into dinitrogen oxide [nitrous oxide] and steam.
(c) A nitrate which gives off oxygen and nitrogen dioxide when heated.
(vii) Name [formula is not acceptable] the gas produced in each of the following reactions: (a) Action of concentrated nitric acid on copper.
(b) Heating of ammonium nitrate (name only the nitrogen containing compounding).
(viii) From the formula listed below, choose one corresponding to the salt having the given
description: AgCl, CuCO3, CuSO4.5H2O, KNO3, NaCl, NaHSO4, Pb(NO3)2, ZnCO3, ZnSO4.7H2O.
This salt gives nitrogen dioxide on heating.
(ix) Give equations for the action of heat on –
(a) NH4Cl (b) NH4NO3.
State whether each reaction is an example of thermal decomposition or thermal dissociation.
(x) Which gas is produced when potassium nitrate is heated. Write the equation for the reaction.
(xi) Name the products formed when ammonium nitrate is heated.
(xii) From the list of the substances given – Ammonium sulphate, Lead carbonate, Chlorine,
Copper nitrate, Ferrous sulphate – State:
A compound which releases a reddish brown gas on reaction with concentrated sulphuric acid
and copper turning.
(xiii) X, Y and Z are three crystalline solids which are soluble in water and have a common anion.
To help you to identify X, Y and Z, you are provided with the following experimental observations.
Copy and complete the corresponding inferences in (a) to (d).
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(a) A reddish-brown gas is obtained when X, Y and Z are separately warmed with concentrated
sulphuric acid and copper turning added to the mixture. The common anion is the _______ ion.
(b) When X is heated, it melts and gives off only one gas which relights a glowing splint. The
cation in X is either ___________ or ___________.
(c) The action of heat on Y produces a reddish-brown gas and a yellow residue which fuses with
the glass of the test tube. The metal ion present in Y is the ___________ ion.
(d) When Z is heated it leaves no residue. Warming Z with sodium hydroxide solution liberates a
gas which turns moist red litmus paper blue. Z contains the ________ cation.
(e) Write the equations for the following reactions: (1) X and concentrated H2SO4 (below 200ºC). (One equation only for either of the cations stated in
(b).).
(2) Action of heat on Y.
Answer : (i) Potassium or Sodium nitrate.
Δ
(ii) (a) 2KNO3 → 2KNO2 + O2.
Δ
(b) 2NaNO3 → 2NaNO2 + O2.
(iii) Nitrous oxide [N2O]
Δ
NH4NO3 → N2O + H2O.
(iv) Potassium nitrate.
Δ
2KNO3 → 2KNO2 + O2.
Lightning
(v) N2 + O2 → 2NO.
discharge
(vi) (a) Potassium nitrate
(b) Ammonium nitrate
(c) Lead nitrate.
(vii) (a) Nitrogen dioxide
(b) Nitrous oxide.
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(viii) Pb(NO3)2.
Δ
(ix) (a) NH4Cl ↔ NH3 + HCl
(b)
Δ
NH4NO3 → N2O + H2O.
Reaction (a) is dissociation and
(b) is decomposition.
(x) Oxygen.
Δ
2KNO3 → 2KNO2 + O2.
(xi) Nitrous oxide and water vapour.
(xii) Copper nitrate.
(xiii) (a) NO3– .
(b) Na+ or K+.
(c) Pb++.
(d) NH4+.
(e) (1) < 200ºC
KNO3 + (conc.) H2SO4 → KHSO4 + HNO3.
Δ
(2) Pb(NO3)2 → 2PbO + O2 ↑ + 4NO2 ↑.