Selina ICSE Solutions for Class 10 Chemistry – Study of Compounds – Nitric Acid
Selina ICSE Solutions for Class 10 Chemistry Chapter 10 Study of Compounds – Nitric Acid
(a) Aqua fortis: Nitric acid is called aqua fortis. Aqua fortis means strong water. It is so called because it reacts with nearly all metals.
(b) Aqua Regia: Conc. Nitric acid (1part by volume) when mixed with conc. Hydrochloric acid (3 parts by volume) gives a mixture called aqua regia. It means Royal water.
HNO3 +3HCl → NOCl +2H2O +2[Cl]
(c) Fixation of Nitrogen: The conversion of free atmospheric nitrogen into useful nitrogenous compounds in the soil is known as fixation of atmospheric nitrogen.
During lightning discharge, the nitrogen present in the atmosphere reacts with oxygen to form nitric oxide.
The nitrogen dioxide dissolves in atmospheric moisture in the presence of oxygen of the air and forms nitric acid which is washed down by the rain and combines with the salt present on the surface of the earth.
4NO2 + 2H2O + O2 → 4HNO3
(b) Concentrated hydrochloric acid cannot replace Conc. Sulphuric acid for the preparation of nitric acid because hydrochloric acid is volatile acid and hence nitric acid vapours will carry HCl vapours.
(c) Conc. Nitric acid prepared in the laboratory is yellow in colour due to the dissolution of reddish brown coloured nitrogen dioxide gas in acid. This gas is produced due to the thermal dissociation of a portion of nitric acid.
4HNO3 → 2H2O + 4NO2 + O2
The yellow colour of the acid is removed:
If dry air or CO2 is bubbled through the yellow acid, the acid turns colourless because it drives out NO2 from warm acid which is further oxidized to nitric acid.
By addition of excess of water, nitrogen dioxide gas dissolves in water and thus the yellow colour of the acid is removed.
(d)The temperature of the mixture of concentrated sulphuric acid and sodium nitrate should not exceed 200oC because sodium sulphate formed at higher temperature forms a hard crust which sticks to the walls of the retort and is difficult to remove. At higher temperature nitric acid may also decompose.
Nitric acid forms a constant boiling mixture with water containing 68% acid. This mixture boils constantly at constant boiling point without any change in its composition. At this temperature, the gas and the water vapour escape together. Hence the composition of the solution remains unchanged. So nitric acid cannot be concentrated beyond 68% by distillation of dilute solution of HNO3.
Iron becomes inert when reacted with nitric acid due to the formation of extremely thin layer of insoluble metallic oxide which stops the reaction.
Passivity can be removed by rubbing the surface layer with the sand paper or by treating with strong reducing agent.
(a) When carbon and conc. Nitric acid is heated the products formed are Carbon dioxide, Nitrogen dioxide and water.
C + 4HNO3 → CO2 + 2H2O + 4NO2
(b) Copper when reacts with dilute HNO3 forms Copper nitrate, Nitric oxide and water.
3Cu + 8 HNO3 → 3Cu(NO3) 2 + 4H2O + 2NO
(a) Reaction of nitric acid with non-metals:
C + 4HNO3 → CO2 + 2H2O + 4 NO2
S + 6 HNO3 → H2SO4 + 2H2O + 6 NO2
(b) Nitric acid showing acidic character:
K2O + 2HNO3 → 2KNO3 + H2O
ZnO + 2HNO3 → Zn(NO3)2 + H2O
(c) Nitric acid acting as oxidizing agent
P4 +20HNO3 → 4H3PO4 + 4H2O + 20NO2
3Zn +8HNO3 → 3Zn(NO3)2 +4H2O +2NO
(a) When Sodium hydrogen carbonate is added to nitric acid sodium nitrate, carbon dioxide and water is formed.
NaHCO3 + HNO3 NaNO3 + H2O + CO2
(b) When Cupric oxide reacts with dilute nitric acid, it forms Copper nitrate.
CuO + 2HNO3 → Cu(NO3)2 + H2O
(c) Zinc reacts with nitric acid to form Zinc nitrate, nitric oxide and water.
3 Zn + 8HNO3 → 3Zn(NO3)2 + 4H2O + 2NO
(d) 4HNO3 → 2H2O + 4NO2 + O2
(a) Sodium nitrate:
NaOH + HNO3 → NaNO3 +H2O
Sodium hydroxide reacts with nitric acid to form sodium nitrate.
(b) Copper nitrate:
CuO + 2HNO3 → Cu(NO3)2 + H2O
Copper oxide reacts with nitric acid to form copper nitrate.
(c) Lead nitrate:
Pb + 4HNO3 → Pb(NO3)2 + 2H2O + 2NO2
Lead reacts with conc. nitric acid to form lead nitrate.
(d) Magnesium nitrate:
Mg +2HNO3 → Mg(NO3)2 + H2
Magnesium with dil. nitric acid to form magnesium nitrate.
(e) Ferric nitrate:
Fe + 6HNO3 → Fe(NO3)3 + 3H2O + 3NO2
Iron reacts with conc. nitric acid to form ferric nitrate.
(f) Aqua regia:
HNO3 + 3HCl NOCl +2H2O + 2[Cl]
Nitric acid reacts with hydrochloric acid to form a mixture called aqua regia.
(a) HNO3 is strong oxidizing agent.
(b) NaNO3 gives NaNO2 and oxygen on heating.
(c) Constant boiling nitric acid contains 68% nitric acid by weight.
(d) Nitric acid turns yellow solution when exposed to light.
The chemical name of the brown ring is Nitroso ferrous sulphate.
Formula: FeSO4. NO
Three important uses of Nitric acid and the property of nitric acid involved is:
|1.||To etch designs on copper and brassware.||Nitric acid act as solvent for large number of metals.|
|2.||To purify gold.||Impurities like Cu, Ag, Zn, etc. dissolve in nitric acid.|
|3.||Preparation of aqua regia.||Dissolves noble metals.|
(a) Brown ring test
- Add freshly prepared saturated solution of iron (II)sulphate to the aq. solution of nitric acid.
- Now add conc. Sulphuric acid carefully from the sides of the test tube, so that it should not fall drop wise in the test tube.
- Cool the test tube in water.
- (iv) A brown ring appears at the junction of the two liquids.
(b) A freshly prepared ferrous sulphate solution is used because on exposure to the atmosphere, it is oxidized to ferric sulphate which will not give the brown ring.
(a) Potassium nitrate
(b) Ammonium nitrate
(c) Lead nitrate
(a) Aqua regia is a mixture of 3 parts Hydrochloric acid and one part Nitric acid.
(b) The catalytic oxidation of ammonia to nitric oxide is exothermic.
(c) Magnesium gives H2 with very dilute nitric acid.
(d) Iron become passive in concentrated nitric acid
Solution 1 (2004).
Solution 1 (2005).
(a) Dilute acid is generally considered a typical acid except for its reaction with metals since it does not liberate hydrogen. It is a powerful oxidizing agent and the nascent oxygen formed oxidizes the hydrogen to water.
(b) 3Cu + 8HNO3 → 3Cu(NO3)2 + 4H2O +2NO
Solution 1 (2006).
(a) All glass apparatus are used because nitric acid vapours are highly corrosive in nature and corrodes cork and rubber etc.
(b) Nitric acid is kept in reagent bottle because nitric acid is a highly fuming liquid; it spreads in air and is highly corrosive.
Solution 1 (2007).
Solution 1 (2008).
Solution 2 (2006).
Solution 3 (2006).
When ammonium nitrate is heated the products formed are nitrous oxide and steam.