CBSE Class 10 Chemistry Electrolysis and Ionization MCQs Set 11

Answer: (d) Silver nitrate

Explanation:
1. Only electrolytes conduct and decompose; silver nitrate is an electrolyte and gives silver at the cathode. Ethyl alcohol, benzene and glucose are non-electrolytes.

Teacher's Note:
1. Electrolytes contain ions in solution.
2. Covalent organic compounds are mostly non-electrolytes.

Answer: (c) electrolytic conduction

Explanation:
1. In electrolytic conduction ions carry the current and chemical changes occur at the electrodes.

Teacher's Note:
1. Metallic conduction involves only the flow of electrons and no chemical change.
2. The process is called electrolysis.

Answer: (c) sodium hydroxide

Explanation:
1. Sodium hydroxide is completely ionised in solution. Ammonium hydroxide and acetic acid are weak electrolytes, and glucose is a non-electrolyte.

Teacher's Note:
1. Strong bases, strong acids and most salts are strong electrolytes.
2. Weak electrolytes ionise only partly.

Answer: (d) cations and anions only (the electrolyte is completely ionised)

Explanation:
1. At infinite dilution every electrolyte, weak or strong, is completely ionised, so only ions remain.

Teacher's Note:
1. Ionisation increases with dilution.
2. No unionised molecules are left at infinite dilution.

Answer: (b) 0.99 and 0.02

Explanation:
1. Hydrochloric acid is a strong acid and is almost completely ionised (about 0.99), while acetic acid is weak and only about 1 to 2% ionised.

Teacher's Note:
1. Strong electrolytes have degrees of ionisation close to 1.
2. Weak electrolytes have very small degrees of ionisation.

Answer: (b) with decrease in the concentration of the solution (dilution)

Explanation:
1. Dilution gives ions more room to move apart and reduces recombination, so the degree of ionisation increases.

Teacher's Note:
1. Ostwald's dilution law explains this.
2. Stirring has no effect.

Answer: (b) it is feebly ionised

Explanation:
1. Only a small fraction of NH₄OH molecules ionise into NH₄⁺ and OH⁻ ions, so the solution has few OH⁻ ions.

Teacher's Note:
1. Strength depends on the degree of ionisation, not on density.
2. Weak bases are weak electrolytes.

Answer: (d) Arrhenius

Explanation:
1. Svante Arrhenius proposed in 1884 that electrolytes dissociate into ions in solution.

Teacher's Note:
1. Faraday gave the laws of electrolysis.
2. Rutherford is known for the nuclear model of the atom.

Answer: (b) dissolves in water to give ions

Explanation:
1. An electrolyte is a substance that gives ions when dissolved in water (or melted); the current only makes the ions move.

Teacher's Note:
1. Ionic solids contain ions but cannot conduct in the solid state.
2. Ions are present before the current is passed.

Answer: (b) the nature of the solute

Explanation:
1. It depends on the nature of the solute, the nature of the solvent, the concentration and the temperature.

Teacher's Note:
1. Strong electrolytes have values near 1.
2. The vessel and the current do not matter.

Answer: (b) on adding excess water to the solution

Explanation:
1. Adding water dilutes the solution and favours ionisation.

Teacher's Note:
1. Higher temperature also favours ionisation.
2. Stirring only mixes the solution.

Answer: (a) on increasing dilution

Explanation:
1. Greater dilution means greater separation of ions, so the degree of dissociation rises towards 1.

Teacher's Note:
1. At infinite dilution it equals 1.
2. Pressure has little effect on solutions.

Answer: (a) 10⁻¹⁴ mol² L⁻²

Explanation:
1. \( K_w = [H^+][OH^-] = 10^{-7} \times 10^{-7} = 10^{-14} \) mol² L⁻² at 25°C.

Teacher's Note:
1. Pure water has [H⁺] = [OH⁻] = 10⁻⁷ M.
2. pH + pOH = 14.

Answer: (a) in water it ionises to give H⁺ and Cl⁻ ions

Explanation:
1. HCl is a covalent molecule in the gas; in water it ionises completely and the ions carry the current.

Teacher's Note:
1. Dry HCl has no free ions.
2. Dry covalent compounds do not conduct.

Answer: (a) Ni²⁺ ions

Explanation:
1. The colour of a salt solution is due to the coloured ion, here hydrated Ni²⁺; sulphate ions are colourless.

Teacher's Note:
1. Copper sulphate is blue because of Cu²⁺ ions.
2. Colourless ions give colourless solutions.

Answer: (a) more ions

Explanation:
1. HCl is a strong electrolyte and is almost completely ionised, while acetic acid is weak and only slightly ionised.

Teacher's Note:
1. Concentration of ions depends on the degree of ionisation.
2. Equal molarity does not mean equal ions.

Answer: (a) a reduction reaction (H⁺ ions gain electrons)

Explanation:
1. H⁺ ions are discharged in preference to Na⁺ ions at the cathode: \( 2H^+ + 2e^- \rightarrow H_2 \), a reduction.

Teacher's Note:
1. Cathode reactions are reductions.
2. Chlorine is liberated at the anode.

Answer: (a) The properties of an electrolyte in solution are the properties of its constituent ions

Explanation:
1. Reactions of solutions of electrolytes are characteristic of their ions. Current in a solution is carried by ions, carbon tetrachloride is a non-electrolyte, and dilution increases ionisation.

Teacher's Note:
1. Ions, not electrons, carry current through solutions.
2. Covalent non-polar liquids do not ionise.

Answer: (a) The blue colour of copper sulphate solution is due to Cu²⁺ ions

Explanation:
1. Cu²⁺ ions are blue. A 10⁻⁸ M acid cannot have pH 8 (acidic solutions have pH below 7, about 6.98 here because of water). Acid solutions have [H⁺] above 10⁻⁷ M, and in electrorefining the impure metal is the anode.

Teacher's Note:
1. Acid solutions have pH less than 7.
2. The anode is the impure metal and the cathode is a strip of pure metal.

Answer: (a) the impure metal is the anode and a thin strip of pure metal is the cathode

Explanation:
1. The impure metal dissolves from the anode and pure metal is deposited on the cathode.

Teacher's Note:
1. The electrolyte is a solution of a salt of the metal.
2. Impurities fall as anode mud.