ELECTROLYSIS

A) ANSWER THE FOLLOWING:

1) What happens to the electrons are the cathode and anode?

2) Pick out the cations and anions from the following:

SO₄²⁻, Pb²⁺, NH₄⁺, OH⁻, NO₃⁻, H⁺, Ag⁺, Cu²⁺, CN⁻, Cl⁻ 

3) What happens when sodium chloride is dissolved in water?

4) The degree of dissociation of sulphurous acid is 20. What is meant by the statement?

5) What is the reason for conductivity in metals?

6) Would you classify sulphurous acid as a strong electrolyte or a weak electrolyte?

7)  Why an electric current is passed through an electrolytic solution ?

8) How a metal like Cu can be  changed into its constituent ions ?

9)  How would you change in Cu²⁺ ion to Cu ?

10) Out of Na and Zn, which is more reactive?

11) why is Na more reactive than Zn?

12) Out of iron and zinc, which is higher in the activity series ?

13) At which electrode are metallic ions discharged during electrolysis?

14) Can Cu be electroplated over Ag ? Why?

15) why cannot we store AgNO₃ solution in Cu vessels?

16) Is electrical energy supplied in an electrochemical cell ?

17) what is the industrial application of the electrolytes CuSO₄ using copper electrodes?

18) Can we store CuSO₄ solution in a Zn vessel? give reason.

19) To which electrode is the impure metal rod connected in the electrolytic refining of a metal?

20) Arrange the following positive ions in the order in which they will be discharged first in preference to others.

Zn²⁺, H⁺, Mg²⁺, Ca²⁺, K⁺, Fe²⁺, Cu²⁺, Na⁺ .

21) Arrange the following ions in the order in which they will be discharged first in preference to others.

Br⁻, Cl⁻, SO₄²⁻, NO₃²⁻, I⁻, OH⁻ 

22) Why is the electrolytic dissociation represented by a reversible sign ? 

23) Which between Zn and Cu would occur more readily in nature as a metal and which as an Ion ? explain.

24)  A solution of caustic soda(NaOH)  in  water or when fused, conducts electric current. What is the similarity in these two cases?

25) During the electrolysis of an aqueous solution of NaCl hydrogen ion is reduced at the cathode and not the sodium ion though both Na⁺, and H⁺ ions are present in the solution. why ?

26) why does cane sugar solution not conduct electricity ?

27)  Define strong and weak acids.

28) What are the particles present in a compound which is a non-electrolyte ?

29) If an electrolyte is the described as a "strong electrolyte", what does this mean ?

30) what is an electrolyte?

31) What should be the physical state of lead bromide if it is to conduct electricity?

31) What particles are present in pure lead bromide?

32) What is observed when a small piece of iron is placed in copper sulphate solution?

33) State what is observed when copper sulphate solution is electrolysed using a platinum anode.

B) GIVE REASON:

1) During electrolysis, the positive ions always get discharged at the cathode.

2) Sea water is a strong electrolyte .

3) copper is a good conductor of electricity but it is a non-electrolyte. 

4) For silver in silverplating, silver nitrate is not used     OR

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

C)  FILL IN THE BLANKS BY CHOOSING THE CORRECT WORD/WORDS GIVEN WITHIN BRACKETS::

1) Powdered sodium chloride (common salt) does not conduct electric current.But it does so when dissolved in ____(alcohol/water)

2) During electrolysis,___Ions move towards the cathode. (Positive/Negative)

3) In an electrolytic cell.___ energy is consumed. (mechanical/electrical)

4) NaCl is a poor conductor of electricity in ____ state.(molten/ solid)

5) Conducting nature of ____ compounds is due to free ions. (ionic/covalent)

6) substances which conduct electricity in the solid state are generally___(metals/nonmetals)

7) The electron releasing tendency of zinc is___ than that of copper. (less/ more)

8) The conductivity of an electrolyte ____with rise in temperature. (decreases/ increases)

9) During electrolysis of copper chloride, _____ is deposited at the cathode.(copper/chlorine)

10) Cations are___ charged ions (negatively /positively)

11) According to ionic theory, the number of Ions ___ with dilution in weak electrolytes. (increases/ decreases)

12) _____ is a weak electrolyte as well as weak acid.(CH₃COOH/NH₄OH)

13) Fe+ CuCl₂ ----> Cu+ ____.(FeCl₃, FeCl₂)

14)  Pure water consists almost entirely of ____(Ions/molecules)

15) We can expect that pure water _____ normally conduct electricity. (will/will not).

16) As we descend the electrochemical series containing cations, the tendency of the cations to get____ at the cathode increases( oxidized/ reduced)

17) The____ the concentration of an ion in a solution, the greater is the probability of its being discharged at its appropriate electrode.(higher/lower)

D) COMPLETE THE FOLLOWING SENTENCES WITH THE HELP OF SUITABLE WORDS:::

1) The metal plate through which an electric current enters into an electrolyte is called ___. it has___ of electrons.

2)  A base is an electrovalent compound which,when dissolved in water, dissociates into A positively charged____ ion and negatively charged___ ion.

3) the ions with discharge on the negative electrode during electrolysis ____electrons and are called ____.

4) In electrorefining of copper, ___ is deposited at the cathode and ___ at the anode.

5) A salt is an electrolyte made up of a positive ion other than__ ion and a negative ion other than ___ ion.

6) With platinum electrodes, hydrogen is liberated at the____ and oxygen at the____ during the electrolysis of acidified water.

7) Electrolysis is the passage of ----- through a liquid or a solution accompanied by a ___ change.

E) NAME THE FOLLOWING::

1) The type of electricity used during electrolysis.

2) The electrode connected to the negative terminal of the battery during electrolysis.

3) two types of electrolytes.

4) The process by which a particle gaines or losers electrons.

5) The process by which an electrovalent compound breaks up into free mobile ions in the molten for Aqueous form.

6) The type of materials through which electricity passes without undergoing any decomposition.

7) The type of substances which undergo the decomposition in aqueous or solution form when an electric current is passed through them.

8) The ions Which discharge on the positive electrode during electrolysis.

9) electrolyte used in silver plating.

10) three metals which can be expected only by electrolysis from their fused salts.

11) A suitable cathode used in the electrorefining of copper.

12) A suitable anode used in the electroplating of iron with silver.

13) The anode used in the extraction of aluminium.

14) A non-metallic element which is a conductor of electricity.

15) The cathode used during electroplating with Nickel.

16) The product at the anode during electrolysis of acidified water with Platinum electrodes.

17) A substance which when dissolved in water contains:

A)  only ions

B) ions and molecules.

18) The gas released at the cathode when acidulated water is electrolysed.

19) A liquid or solution, which conducts electricity with accompanying chemical change.

20) A solution of this compound is used as the electrolyte when copper is purified.

21) when this compound is electrolysed in the molten state, lead is obtained at the cathode.

F) STATE WHETHER TRUE OR FALSE also, correct the incorrect statements:::

1) In an electrolyte, the number of positive ions is equal to the number of negative ions.

2) During electrolysis, oxidation occurs at the cathode and reduction occurs at the anode.

3) When dilute sulphuric acid is electrolysed. sulphur is precipitated at the anode.

4) Ions are the particles which exist only in water solutions.

5) In an electrolyte, the current flows because the molecules migrate to the charged plates (electrodes).

6) To carry out the electrolysis of water, sulphuric acid to it.

7) Copper sulphate crystals are dehydrated by sulphuric acid.

8) the electrolysis of lead bromide liberates lead and bromine.

G) CHOOSE THE CORRECT ANSWER FROM THE CHOICES.

 

1) During the electrolysis of fused NaCl, which of the following reactions occur at the cathode ?

A) Na⁺ ions are used

B) Na⁺ ions are reduced.

C) Cl⁻ ions are reduced.

D) Cl⁻ ions are oxidised

2) Which one of the following compounds will decompose when electricity is passed through their aqueous solutions

A) sugar                    B) urea 

C) copper sulphate D) ethyl alcohol

3) point out the incorrect statement:

A) the electrode at which oxidation takes place is known as anode.

B) the electrode at which the reduction takes place is called cathode.

C) the electrode at which electrons are gained is called cathode.

D) the electrode at which electrons are lost is called cathode.

4) In the electrochemical series, the reducing character of the elements from top to bottom:

A)  increases B) decreases

C) remain unchanged  D) none

5) The flow of current in an electrolyte is due to the movement of:

A) electrons  B) protons

C) Ions           C) molecules

6) The Ions present at the anode during during electrolysis of molten lead bromide are:

A) Pb²⁺ions B) Br⁻ions

C) Br ²⁻ ions  D) none

7) During electrolysis of acidified water, the ratio of hydrogen and oxygen liberated at the cathode and anode is:

A) 1:2.    B) 2:1  C) 3:1 D) 2:3

8) During electrolysis of aqueous copper sulphate, the reaction at the anode is:

A) Cu²⁺ + 2e⁻ ---> Cu 

B) Cu - 2e⁻ ---> Cu²⁺

C) Cu+ 2e⁻ ---> Cu²⁻ 

D) Cu - e⁻  ----> Cu⁺

9) On heating chlorides react with:

A) dilute acids.  B) volatile acid

C) conc. volatile acids

D) conc.non volatile acids.

H) COMPLETE THE FOLLOWING REACTION

A) Na⁺ + _______ ---> Na

B) Cl⁻ - 1e⁻ ---> ______

C) Pb²⁺ + ______ ---> Pb

D) 4H⁺ + _______ ---> 2H₂ 

E) Ag⁺ + ______ ---> Ag

F) 4OH⁻ -- 4e⁻ ---> ___+_____

G) Cu²⁺+ 2e⁻ ---> ____

H) Cu - 2e⁻ ---> _______

I) Na - 1e⁻ -----> _____

J) CH₃COOH <=> _____+ ____

K) H₂SO₄ <=> ____+ ____

L)Write the equation for the reactions which takes place at the electrodes during the electrolysis of lead Bromide.

I) ANSWER THE FOLLOWING:

1) Each of the following statement contains an error. Explain that error:

A) On passing an electric current through a solution of sodium chloride, the sodium chloride splits into positive and negative ions.

B) When an electric current is passed through sugar solution, no decomposition occurs.

2) In this question you are required to use the word (or words) that will make each sentence into correct statement which is written down in full.

A) calcium nitrate react with sodium sulphate to form calcium sulphate (same is required in two places)

B) crystals of sulphur are obtained when a solution of sulphur in carbon disulphide is allowed to evaporate.

3) when the electrolysis of acidified water is carried out:

A) what is the ratio of volume of hydrogen to the volume of oxygen ?

B) give the Equation for the discharge of ions at the cathode.

4) To carry out so-called "electrolysis of water" sulphuric acid is added to water. How does the addition of Sulphuric and produce a conducting solution ?

5) Acids dissolve in water to produce positively charged ions. Draw the structure of these positive ions 

6) How is the electrolysis of aqueous NaCl different from molten NaCl ?

7) Give one example in each case of a substance which contains:

A) ions only 

B) molecules only 

C) both ions and molecules

8) Electrolysis is used in the purification of metals. Name:

A) the anode 

B) The cathode

C) the electrolyte

 you would use to get pure copper from a piece of impure copper.

9) Classify the following substances under three headings:

a) Strong electrolytes, 

b) Weak electrolytes, c) Non-electrolytes

 Acetic Acid, ammonium chloride, Ammonium hydroxide, carbon tetrachloride, dilute hydrochloric acid, sodium acetate, dilute sulphuric acid.

10) Fill in the blanks with the suitable words.

 Solid lead(II) Bromide will not conduct an electrical current. The ____ are held in the rigid crystal ____ and are not free to move to the _____.when the solid is ___. It allows the passage of an electric current. Lead is liberated at the ___ and bromine at the the ____. The decomposition of an electrolyte by an electric current is called _______.

11) During electroplating, explain why:

A) a direct current is used.

B) a small current should be used for a long time.

C) the article to be electroplated should always be placed at the cathode.

D) the anode must be made of the metal with which the article has to be plated.

12) Consider that the following lines to be present in an electrolyte:

 Na⁺ , K⁺ , H⁺ , S0₄²⁻, Cl ⁻ , OH⁻ ,

if Platinum electrodes are used in its electrolysis:

A) name the ions that would be discharged at the anode.

B) name the ions that would be discharged at the cathode.

C) give a reason to support your answer in A and B.

D) summarise the ionic reactions taking place at the cathode and at the anode.

13) Copy and complete the following table:

ELECTROLYSIS OF WATER WITH SULPHURIC ACID

-----------------------------------------------------

                          cathode   anode

A) electrode used  ------    ------

B) ions present      ------    ------

C) products            -----     ------

D) Reactions          -----      -----

14) State two applications of electrolysis.

15) write the equations of the reactions which take place at the cathode and anode when dilute sulphuric acid is electrolysed with platinum electrode.

16) Answer the following questions about electroplating a copper wire with silver:

A) What ions must be present in the electrolyte

B) of what substance must the anode be made ?

C) What will be made the cathode?

D) What is the Equation for the reaction which takes place at the cathode ?

17) Give the formula of ions present in:

A) aqueous solution of Ammonium hydroxide.

B) aqueous solution of CuSO₄  

C) aqueous solution of NaCl

D) molten sodium chloride(NaCl)

E) water attitude acidified with H₂SO₄ 

18) The table given below refers to the electro refining of Copper and electroplating with nickel. complete the table.

                E.R of Cu    R. P of nickel

Electrolyte used  ---        ------

Electrodes   anode ---   anode ----

                  Cathode ---  cathode ----

Reaction at anode ----        -------

Reaction at cathode---      -------

19) Fill in the blanks with suitable words :

Molten lead Bromide conducts electricity. it is called an___. it is composed of lead____ and bromine ____. The lead____ are called ____. The bromine ___ are__ charged and are called____.

20) What to do you observe in the following cases:

A)  A copper plate and a zinc plate ate dipped into dilute sulphuric acid and connected externally by a metal wire connected through a galvanometer or a small bulb.

B) Acidified water is electrolysed between platinum electrodes.

C) Ammonium hydroxide is electrolysed between carbon electrodes.

D) molten sodium chloride is electrolysed between carbon electrodes.

E) Aqueous copper sulphate solution is electrolysed between copper electrodes.

21) write the equation for the reaction between: 

A) CH₃COONa and H₂SO₄.

B) K₂O and H₂SO₄ (dil)

C) KNO₃ and H₂SO₄(conc.)

D) Zn and KOH

E) SnO₂ and KOH 

22) The following questions relate to the electroplating of an article with silver:

A) Name the electrode formed by the article to be plated.

B) What ions must be present in the electrolyte?

C) What should be the nature of the anode?

D) How is the passage of electricity through an electrolyte different from the passage of electricity through a copper wire?

22) element X is a metal with valency 2. Element Y is a non metal with valency 3.

A) write equations to show how X and Y form ions.

B) If Y is a diatomic gas, write the equation for the direct combination of X and Y to form a compound.

C) write two applications of electrolysis in which the anode diminishes in mass.

D) If the Compound formed between X and Y is melted and an electric current passed through the molten compound, the element X will be obtained at the___ and Y at the _____ of the electrolytic cell.

(Provide the missing words)

23) Choosing only from the following list, write down the appropriate words to fill in the blanks:::

(Anions, anode, cathode, cations, electrode, electrolyte, nickel, voltameter) 

To electroplate an article with nickel requires an____ Which must be a solution containing____ ions. The article to be plated is placed at the ____ of the cell in which the plating is carried out. The____ of the cell is made from pure nickel. The ions which are attracted to the negative electrode and discharged are called____.

24) Choose A, B, C, D to match the description (i) to (iv). Some alphabet may be repeated.

A) Non-electrolyte 

B) Strong electrolyte 

C) Weak electrolytes

D) Metallic conductor

i) molten ionic compound 

ii) carbon tetrachloride 

iii) An Aluminium wire 

iv) a solution containing solvent molecules, solute molecules and ions formed by dissociation of solute molecules.

v) A sugar solution with sugar molecules and water molecules.

J) REASON BEHIND:

1) why is it necessary to add acid to water before proceeding with the electrolysis of water ?

2) why are electrode reactions called redox reaction ?

3) why metals like potassium, calcium, sodium, etc., can be extracted only by electrolysis.

4) Why copper, though a good conductor of electricity, is a non-electrolyte.

5) why solid sodium chloride does not allow electricity to pass through.

6)  why carbon tetrachloride does not dissolve in water ?

7) What is the purpose of electroplating ?   OR

why is electroplating done ?

 

K) DIFFERENTIATION BETWEEN:

1) electrolyte/ non-electrolytes

2) strong electrolytes/weak electrolytes

3) cathode/anode 

4) conductors/ electrolytes

5) Ionization/electrolytic dissociation dissociation 

6) Anions/Captions

7) atoms/ions