Chemistry

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Q. 1. During the electrolysis of molten lead bromide, which of the following takes place :  A : Bromine is released at the cathode. B: Lead is deposited at the anode.  C : Bromine ions gain electrons. D: Lead is deposited at the cathode. Ans : - D.

Q. 2. Here is an electrode reaction : Cu → Cu2+ + 2e-. [i.e. Cu- 2e- →Cu2+]. At which electrode(anode or cathode) would such a reaction take place. Is this an example of oxidation or reduction. Ans : - At anode. Oxidation.

Q. 3. A solution contains magnesium ions(Mg2+), iron (II) ions (Fe2+) and copper ions (Cu2+). On passing an electric current through this solution which ions will be the first to be discharged at the cathode. Write the equation for the cathode reaction. Ans.: - Mg2+

Q.4. An electrode ‘A’ is connected to the positive terminal of a battery and electrode ‘B’ to the negative terminal.  (i) Give the names of the electrodes A & B.
(ii) Which electrode is the oxidizing electrode.
Ans : - (i) A – Anode, B – Cathode. (ii) A.
Q. 5. State the appropriate term used for : – A liquid or solution, which conducts electricity with accompanying chemical change. Ans.: - Electrolytes.
Q.6. Electrons are getting added to an element Y. 
(i) Is Y getting oxidized or reduced? 
(ii) What charge will Y have after the addition of electrons?  (iii) Which electrode will Y migrate to during electrolysis? Ans : - (i) Reduced (ii) Negative (iii) Anode
Q. 7. Explain how electrolysis is an example of redox reaction. Ans.: - A redox reaction is one in which reduction and oxidation occurs simultaneously.  (i) Cathode (Reducing electrode) : – At cathode, the cations gain electrons to form neutral atoms. As electrons are gained, the ion is said to be reduced.  (ii) Anode (Oxidizing electrode) : – At anode, the anions lose electrons to form neutral atoms. As electrons are lost, the ion is said to be oxidized. Q. 8. What kind of particles will be found in a liquid compound which is a non-electrolyte? Ans.: - Molecules.

Q.9. Complete the sentence by choosing the correct words – Electrolysis is the passage of ………… [electricity / electrons] through a liquid or a solution accompanied by a …………. [physical / chemical] change. Ans.: - Electricity, Chemical.

Q.10. Name a liquid which is a non-electrolyte.
Ans.: - Alcohol.
Q.11. Name one substance which contains : (i) ions only (ii) molecules only (iii) both ions and molecules. Ans.: - (i) NaOH (ii) Alcohol (iii) NaCO3.
Q. 12. (i) What is meant by the term ‘electrolyte’. 
(ii) What are the particles present in a compound which is non-electrolyte?  (iii) If an electrolyte is described as a ‘strong electrolyte’, what does this mean. Ans : - (i) Chemical compounds which conduct electricity either in a fused or in aq. solution state and undergo chemical decomposition due to the flow of current through it are called electrolytes.  (ii) Molecules only. 

(iii) (a) They are electrolytes which allow a large amount of electricity to flow through them and hence are good conductors of electricity.  (b) Are almost completely dissociated in fused or aqueous solution state.  (c) The solution contains almost only free mobile – ions.

Q. 13. Explain why (i) solid sodium chloride does not allow electricity to pass through. (ii) copper, though a good conductor of electricity , is a non-electrolyte. Ans : - (i) In sodium chloride, Na+ and Cl - ions are not free to carry the electric current.  (ii) Copper metal is solid and has no mobile ions whereas an electrolyte should dissociate into oppositely charged ions to conduct the electric current. Q. 14. Classify the following substances under three headings: (i) Strong Electrolytes (ii) Weak Electrolytes (iii) Non Electrolytes – Acetic acid, ammonium chloride, ammonium hydroxide, carbon tetrachloride, dilute hydrochloric acid, sodium acetate, dilute sulphuric acid. Ans : - (i) Strong Electrolytes – Ammonium chloride, dilute hydrochloric acid, dilute sulphuric acid.  (ii) Weak Electrolytes – Ammonium hydroxide,...
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