NCERT Solution: Chemical Reactions and Equations
Calcium oxide
CaO(s) + H2O(l) → Ca(OH)2(aq)
(a) Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.
Ans. Pb(CH3COO)2 + HCl → PbCl2 + CH3COOH
This is a Double Displacement reaction
(b) A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.
Ans. 2Na + 2C2H5ONa + H2
(c) Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.
Ans. 2Fe2O3 + 3CO → 2Fe + 3CO2
This is decomposition reaction.
(d) Hydrogen sulphide gas reacts with oxygen gas to form solid Sulphur and liquid water.
Ans.
2H2O + O2 -> 2S + 2H2O
This is a Redox reaction.
Silver chloride on exposure to sunlight may decompose as per the following reaction.
2 AgCl → 2Ag + Cl2
Therefore, it is stored in dark coloured bottles.
(a) Write the chemical formulae of X and Y
Ans. X is MgO Y is Mg3N2
(b) Write a balanced chemical equation, when X is dissolved in water.
Ans. MgO + H2O → Mg(OH)2
Zinc is above hydrogen whereas copper is below hydrogen in the activity series of metals. That is why zinc displaces hydrogen from dilute hydrochloric acid, while copper does not.
Zn + HCl → ZnCl2 +H2
Cu + HCl → No reaction
(a) Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.
Ans. Metals such as silver when attacked by substances around it such as moisture, acids, gases etc, are said to corrode and this phenomenon is called corrosion.
(b) Name the black substance formed and give its chemical formula.
Ans. The black substance is formed because silver (Ag) reacts with H2S present in air. It forms thin black coating of silver sulphide (Ag2S)
(a) Write a balanced chemical equation of the reaction.
Ans. Balanced chemical equation
2Cu(NO3)2(s) → 2CuO +O2 + 4NO2(g)
(b) Identity the brown gas X evolved.
Ans. The brown gas X evolved is nitrogen dioxide (NO2).
(c) Identity the type of reaction.
Ans. This is a decomposition reaction
(d) What could be the pH range of aqueous solution of the gas X?
Ans. Nitrogen dioxide dissolves in water to form acidic solution because it is an oxide of non-metal. Therefore, pH of this solution is less than 7.