ELECTROLYSIS - 10 ICSE CHAPTER WISE QUESTIONS

     Electrolysis     

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Short Answer Questions

1.      Name the particles present in a compound which is a non electrolyte.

2.      Why is it necessary to add acid to water before proceeding with the electrolysis of water?

3.      Explain why is solid NaCl a very poor conductor while if melted is good conductor of electricity.

4.      Why are articles electroplated?

5.      Name the substance which is a good conductor of electricity but a bad conductor of heat.

6.      Which particles are present in solid lead(II) bromide and molten lead(II) bromide?

7.      Explain why a direct current should be used during electroplating.

8.      A small current should be used for a longer time during electroplating. Explain.

9.      Write the main applications of electrolysis.

10.  Explain why pure water does not conduct electricity.

11.  How is the passage of electricity through an electrolyte different from the passage of electricity through copper wire?

12.  State three applications of electrolysis.

13.  Give reasons why a solution of AgNO3 is a good electrolyte but it is not used in electroplating an article with silver.

14.  What is electroplating? State its impotantce.

15.  Write two applications o electrolysis in which the anode diminishes in mass.

Long Answer questions

1.      Define electrolysis, Electrolyte & Non Electrolyte.

2.      Differentiate between

a. Electrolyte & Non Electrolyte.                            b. Atom & an Ion       

c. Weak electrolyte and strong electrolyte.         d. Cation & Anion.

3.      Electrolysis of Molten Lead Bromide:

a.       What should be the physical state of lead bromide, if it has to conduct electricity?

b.      What particles are present in pure Lead bromide?

c.       Why is the electrolytic cell made of silica?

d.      Summarise the electrode reactions.

e.       Complete the following paragraph by inserting one of the following words in each blank space:    [heated, lead,ions, electrolysis, lattice, melts, electrode, bromine]                  

Solid lead(II)bromide will not conduct electricity. The _________are held in a rigid crystal __________ and are not free to move to the _______. When the solid is ______________ it _________ and allows the passage of electric current. ____________ is liberated at the cathode and ___________ at anode. The decomposition of an electrolyte by an electric current is called _______________

4.      Electrolysis of acidified water or dilute sulphuric acid:

With reference to the electrolysis of acidulated water, answer the following:

a.       Explain why distilled water is a non-electrolyte.

b.      What is the electrolytic cell called?

c.       Name the gas released at the Cathode and Anode during the electrolysis of acidulated water.

d.      Explain why the cathode and anode are made up of platinum foil.

e.       Complete the table given below for the electrolytic reactions.

f.       Explain why the volume of hydrogen to oxygen evolved is in the ratio o 2:1.

g.      To carry out so called electrolysis of water, sulphuric acid is added to water. How does the addition of sulphuric acid produce a conducting solution?

h.      Complete the following sentences with suitable words of phrases form the brackets.

i.        Pure water consists almost entirely of _________________(ion/molecules). We can expect the pure water __________________(will/will not) normally conduct electricity.

ii.      Electrolysis is the passage o ________________(electricity/electrons) through a liquid or a solution accompanied by a ___________________(Physical/chemical change)

iii.    With platinum electrodes hydrogen is liberated at the ______________ and oxygen at the _______________ during electrolysis of acidified water.

5.   Electrolysis of CuSO4 solution:

a.       State the ions present in CuSO4 soluton.

b.      Products at the electrodes(Cathode and Anode) during electrolysis of copper sulphate.

c.       Compare the change in mass of cathode with change in mass of anode.

d.      What is seen to happen to the colour of CuSO4 solution if platinum electrodes are used?

e.       Explain why the blue colour of the copper sulphate solution does not fade during its electrolysis using Cu electrodes.

f.       Explain why during the electrolysis of CuSO4 using Cu electrodes, Cu and H ions migrate towards the cathode but only Cu ions are discharged.

g.      Complete the electrolytic reaction of the above electrolysis.

6.   Electroplating with silver:                                                                                                 

a.       Name the electrode formed by the article to be plated.

b.      What ions must be present in the electrolyte?

c.       Name the electrolyte used.

d.      What should be the nature of the anode?

e.       Complete the electrolytic reaction of the above electrolysis.

7.   Electroplating with Nickel:

a.       Name the electrodes.

b.      Name the electrolyte used.

c.       Complete the electrolytic reactions of the above electrolysis.

8.   Choose words from the following list, write appropriate words to fill the blank spaces.

[anion, anode, cation, cathode, electrode, electrolyte, nickel, voltameter]

To electroplate an article with nickel requires on _______________, which must be a solution containing ____________________ ions. The article to be plated is placed as the ________________ of the cell, in which plating is carried out. The ____________ of the cell is made from pure nickel. The ions which are attracted to negative electrode and discharged are called _________________.

9.   The diagram represents the arrangement for the electro refining of copper.

Electrolysis is used the purification of metals. Name the following with reference to the electrorefinfing of copper.

a.       Anode used  b. Cathode used  c. Electrolyte used  d. The product formed at anode.    e.The product formed at cathode.

Explain why

i)                    The concentration of the aqueous copper sulphate, does not change during the electro refining process.

ii)                  During electrorefining  of copper, the aqueous copper sulphate is acidified with dilute acid.

f.       Complete the table given below for the electrolytic reaction.

10.  Give reasons for the following:

a.       Metals above Zn in the activity series of metals are extracted from their ores by electrolysis.

b.      Extraction of sodium is carried out by electrolysis of NaCl in molten or fused state only.

11.  Complete the following table which refers to two practical applications of electrolysis:

12.  Classify the following into: Non electrolyte, Weak electrolyte & Strong electrolyte.           CH3COOH, NH4Cl, NH4OH, CCl4, dil.HCl, CH3COONa, dil.H2SO4.

13.  Choose from the following list the one which contains:   

  a. only ions      b. only molecules            c. molecules and ions

 [dil.CH3COOH, fused PbBr2, H2CO3, CCl4, NH4OH, NaCl, C12H22O11, distilled H2O, C6H6, (CH3COO)2Pb, Petrol, alcohol]

Conceptual questions

1.      Why is the electrolysis of acidulated water considered as an example of catalysis?

2.      Prolonged electrolysis of CuSO4 solution between platinum electrodes, results in the formation of hydrogen gas at the cathode and oxygen gas at the anode. Why?

3.      When a zinc rod is placed in a solution of silver nitrate, a white ppt is formed while no ppt is formed when a silver rod is dipped in a solution of Zinc nitrate. Explain?

4.      Why is copper sulphate solution not kept in iron vessels?

5.      A solution of cane sugar does not conduct electricity but a solution of NaCl is a good conductor. Give reason.

6.      In the electrolysis of acidified water dilute sulphuric acid is preferred to dilute nitric acid for acidification. Explain

Previous years ICSE exam questions

1.      Match the substance from the following list with appropriate description given below:       a. sulphur         b. AgCl   c. HCl  d. CuSO4        e. Graphite                 

A pink metal which is deposited at the cathode during the electrolysis of the solutions of this salt.

2.      Why is carbon tetrachloride, which is a liquid, a non electrolyte?

3.      What is observed when copper sulphate solution is electrolysed using a platinum anode?

4.      Identify the following reactions as either oxidation or reduction:                                        

 a. O     +          2e-     --->                   O-2      b. K     --->        e-    K+1                

 c. Fe+3            +          e-     --->                Fe+2

5.      A solution of silver nitrate is a good electrolyte but it is not used for electroplating an article with silver. Give reason.

6.      Electrons are getting added to element Y. Which electrode will Y migrate to during electrolysis?

7.      Write two applications of electrolysis in which the anode diminishes in mass.

8.      What kind of particles will be found in a liquid which is a non electrolyte?

9.      Name the liquid which is a non electrolyte.

10.  Name a solid which undergoes electrolysis when molten.

11.  To carry out the so called ‘electrolysis of water’, sulphuric acic is added to water. How does the addition of sulphuric acid produce a conducting solution?

12.  Classify the following substances under strong electrolytes, weak electrolytes and non electrolytes:            acetic acid, NH4Cl, dil.HCl, CH3COONa and dil.H2SO4.

13.  What is an electrolyte?

Long answer Questions

1.      During electrolysis of CuSO4 solution using platinum as cathode and carbon as anode:     

a. What do you observe at the cathode and at the anode?      

b. What change is noticed in the electrolyte?       

c. Write the reactions at the cathode and at the anode.

2.      Differentiate between the electrical conductivity of CuSO4 solution and Cu metal.

3.      Why is the electrolysis of acidulated water considered as an example of electrolysis.

4.      Mr. Ramu wants to electroplate his key chain with nickel to prevent rusting. For this electroplating,                     

a. Name the electrolyte; b. Name the cathode ; c. Name the anode  

d. Give the reactions at anode.    e. Give the reactions at cathode

5.       Three different electrolytes A, B and Care connected in separate circuits. Electrolytic cell A contains sodium chloride solution. When the circuit is completed a bulb in the circuit glows brightly. Electrolytic cell B contains acetic acid solution, and in this case the bulb in the circuit glows dimly. The electrolytic cell C contains sugar solution and the bulb does not glow. Give a reason for each of these observations.

6.      A metal article is to be electroplated with silver. The electrolyte selected is sodium argentocyanide.                                                

A. what kind of salt is sodium argentocyanide?    

B. why is it preferred to silver nitrate as an electrolyte?  

c. State one condition to ensure that deposit is smooth, firm and long-lasting.           

D. Write the reaction taking place at the cathode. 

E. Write the reaction taking place at the anode.

7.   Aqueous solutions of nickel sulphate contains Ni+2 and SO4-2. 

A. Which ion moves toward the cathode?  

B. What is the product at the anode?

8.      A. Given below is an electrode reaction: Cu(s)     ---->         Cu+2(aq)         +          2e-

At which electrode would such a reaction take place? Is this an example of oxidation or reduction?

B. A solution contains Mg+2 ion, Fe+2 ion and Cu+2 ion. 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.                                                         

C. Why is Carbon tetrachloride, which is a liquid, a non electrolyte?

9.      Choose A, B, C or D to match the descriptions (a) to (e) given below. Some alphabets may be repeated.   A. Non electrolyte  

B. Strong electrolyte    C. Weak electrolyte  D. Metallic conductor  

(a) Molten ionic compound            (b) Carbon tetrachloride 

(c) Aluminium wire                         

(d) A solution containing solvent molecules, solute molecules and ions formed by the dissociation of solute molecules.                          

(e) A sugar solution with sugar molecules and water molecules.

10.  A. Study the diagram given below and answer the questions that follow:  (electrolytic cell diagram)   

I. Give the name of the electrodes A and B.  

II. Which electrode is the oxidizing electrode?                     

B. A strip of copper is placed in four different colourless salt solutions. They are KNO3, AgNO3, Zn(NO3)2, and Ca(NO3)2. Which one of the solutions will finally turn blue?                                    

C. Write the chemical equations of the reactions which takes place at the cathode and at the anode when acidified water is electrolysed.

11.   A. Explain why copper, though a good conductor of electricity, is a non – electrolyte

B. Name the gas released at the cathode when acidulated water is electrolysed.

C. Explain why solid sodium chloride does not allow electricity to pass through it.

12.  . A. Provide the missing words:    Element X is a metal with valency 2. Element y is a non metal with valency 3. If the compound formed between X and Y is melted and an electric current is passed through the molten compound, the element X will be obtained at the _______ and Y at the ___________ of the electrolytic cell.

B. i. What kind of particles will be found in a liquid compound which is a non – electrolyte?

ii. If HX is a weak acid, which particles will be present in its dilute solution apart from those of water?

iii.Which ions must be present in a solution used for electroplating a particular metal?

iv.    Explain how electrolysis is an example of redox reaction.

13.  Copy and complete the following table which refers to two practical applications of electrolysis:

	Anode	Electrolyte	Cathode
Silver plating of spoon		Solution of potassium argentocyanide
Purification of Cu