CBSE Class 10 Physics Chemical Effects of Electric Current MCQs Set 04

Answer: (c) galvanic cell

Explanation:
1. A galvanic (voltaic) cell produces an electric current from a chemical reaction.

Teacher's Note:
1. It is a source of emf.

Answer: (d) direct current

Explanation:
1. A steady DC makes the cathode always negative and the anode always positive.
2. With AC the electrodes would keep reversing polarity.

Teacher's Note:
1. A battery or a rectifier supplies the DC.

Answer: (a) hydrogen and oxygen

Explanation:
1. Hydrogen ions are reduced at the cathode to give hydrogen.
2. Hydroxide ions or water are oxidised at the anode to give oxygen.

Teacher's Note:
1. The volume of hydrogen is twice the volume of oxygen.

Answer: (b) increases

Explanation:
1. A rise in temperature lowers the viscosity of the solution and increases ionisation.
2. Ions move more easily, so conductivity increases.

Teacher's Note:
1. The conductivity of a metal, on the other hand, decreases as it is heated.

Answer: (c) dilute sulphuric acid

Explanation:
1. A lead storage battery uses dilute sulphuric acid with lead and lead dioxide plates.

Teacher's Note:
1. It is a rechargeable (secondary) cell.

Answer: (d) all of the above

Explanation:
1. Electrolysis is used to extract reactive metals like sodium and aluminium, to refine copper and to electroplate objects.

Teacher's Note:
1. All three are industrial uses.

Answer: (d) acetic acid

Explanation:
1. Acetic acid is only partly ionised in water, so it gives few ions.
2. The others ionise completely.

Teacher's Note:
1. Weak electrolytes are poor conductors.

Answer: (d) HCl

Explanation:
1. HCl is a strong electrolyte that ionises completely in water.
2. Sugar and alcohol dissolve as molecules, and pure water has too few ions.

Teacher's Note:
1. Solutions of most organic compounds do not conduct.

Answer: (b) does not dissolve or react with the products of electrolysis

Explanation:
1. Platinum is chemically unreactive and conducts well.
2. It does not take part in the reactions.

Teacher's Note:
1. Copper electrodes would dissolve into the solution.

Answer: (c) a liquid that conducts electricity

Explanation:
1. An electrolyte is a substance that conducts electricity in the molten state or in solution through the movement of ions.

Teacher's Note:
1. Metals conduct through electrons and are not electrolytes.

Answer: (b) reduction of a positive ion takes place

Explanation:
1. Cations move to the cathode and gain electrons there.
2. Gain of electrons is reduction.

Teacher's Note:
1. Remember: reduction at the cathode, oxidation at the anode.

Answer: (a) Cl\( ^- \) is oxidised at the anode

Explanation:
1. Negative ions go to the anode.
2. Cl\( ^- \) loses an electron there: 2Cl\( ^- \) \( \rightarrow \) Cl\( _2 \) + 2e\( ^- \), which is oxidation.

Teacher's Note:
1. Oxidation always takes place at the anode.

Answer: (c) electrical energy to chemical energy

Explanation:
1. In an electrolytic cell an external source supplies electrical energy.
2. It is used to bring about a chemical change.

Teacher's Note:
1. In a galvanic cell the conversion is the other way round.

Answer: (a) anode

Explanation:
1. The positively charged electrode is called the anode, and negative ions move towards it.

Teacher's Note:
1. The cathode is the negative electrode of an electrolytic cell.

Answer: (b) increase the number of free ions and the conductivity

Explanation:
1. Pure water has very few ions and conducts poorly.
2. The acid supplies free ions and increases the conductivity.

Teacher's Note:
1. The acid itself is not consumed in the process.

Answer: (b) solid NaCl

Explanation:
1. In solid NaCl the ions are held in fixed positions and cannot move.
2. Graphite has free electrons, and the two solutions contain free ions.

Teacher's Note:
1. NaCl conducts when molten or dissolved in water.

Answer: (b) a poor conductor of electricity

Explanation:
1. Pure water has very few free ions.
2. So it is a very poor conductor.

Teacher's Note:
1. A little acid or salt makes water conduct well.

Answer: (a) 2 : 1

Explanation:
1. The reaction is 2H\( _2 \)O \( \rightarrow \) 2H\( _2 \) + O\( _2 \).
2. Two moles of hydrogen are formed for each mole of oxygen, so the volumes are in the ratio 2 : 1.

Teacher's Note:
1. The test is a useful way to remember the formula H\( _2 \)O.

Answer: (b) towards oppositely charged electrodes

Explanation:
1. Positive ions move to the cathode and negative ions to the anode.

Teacher's Note:
1. Electrolytic conduction is due to the movement of ions.

Answer: (c) remains the same

Explanation:
1. At the cathode Cu\( ^{2+} \) + 2e\( ^- \) \( \rightarrow \) Cu removes copper ions from the solution.
2. At the copper anode Cu \( \rightarrow \) Cu\( ^{2+} \) + 2e\( ^- \) adds the same amount.
3. So the concentration stays the same.

Teacher's Note:
1. Copper is transferred from anode to cathode.