C6 - Electrolysis

Question 1

What is electrolysis?

Answer 1

Electrolysis is the process of decomposing compounds, when they are in solution or when they are melted.

Question 2

How does electrolysis work?

Answer 2

When passing an electric current through the solution or melted compound, two products are formed, one at the cathode and one at the anode.

Question 3

What is the anode?

Answer 3

The anode is the positive electrode.

Question 4

Which is the negative electrode?

Answer 4

The negative electrode is the cathode.

Question 5

What is the electrolyte?

Answer 5

The electrolyte is the solution or molten compound in which the electric current is passed through. It can conduct electricity and is decomposed during electrolysis.

Question 6

What do electrodes do?

Answer 6

They ‘dip into’ the electrolyte and attract ions.

Question 7

What are positive ions attracted to? Why?

Answer 7

Positive ions are attracted to the negative electrode (CATHODE) because opposites attract.

Question 8

What type of ions are attracted to the anode?

Answer 8

Negative ions are attracted to the anode.

Question 9

What are positive ions called?

Answer 9

Positive ions are called cations.

Question 10

What are anions?

Answer 10

Anions are negative ions.

Question 11

What formula do cations have? Give an example of a cation.

Answer 11

Cations have a positive charge, therefore they have ‘+’ at the end of them. (EXAMPLE = H+ or K+)

Question 12

What formula do anions have? Give an example of an anion.

Answer 12

Anions have a negative charge, therefore they have a ‘-“ at the end of them. (EXAMPLE = OH- or CL-‘

Question 13

What two products would be formed if molten sodium chloride was electrolysed? What are the charges?

Answer 13

Sodium and Chloride. Na+ and Cl-

Question 14

If sodium is positively charged, where will it be formed?

Answer 14

The negative electrode, the cathode.

Question 15

If chlorine is negatively charged, where will it be formed?

Answer 15

The positive electrode, the anode.

Question 16

Why does an electrolyte have to be liquid?

Answer 16

Electrolytes are ionic, so the only way the power supply can make charge move is by making the ions move. If the electrolyte is a solid, the ions are in a fixed position and cannot move.

Question 17

What is the ionic half equation for sodium? Remember, sodium is positively charged.

Answer 17

Na+ + e- –> Na

Question 18

What is the ionic half equation for chlorine?

Answer 18

2Cl- - 2e- –> Cl2

Question 19

What are the two ionic half equations for potassium chloride?

Answer 19

2K+ + 2e- –> K

2Cl- - 2e- –> Cl2

Question 20

What tests can you do to find out which gasses are produced during electrolysis of sulfuric acid?

Answer 20

Hold a lighted splint in hydrogen and it burns with a pop.

Hold a glowing splint in oxygen and it relights the splint.

Question 21

Which electrode does hydrogen discharge at? Remember hydrogen is positively charged.

Answer 21

The cathode.

Question 22

Which electrode does oxygen discharge at? Remember oxygen is negatively charged.

Answer 22

The anode.

Question 23

Which electrode becomes coated with copper and why?

Answer 23

The cathode becomes coated with copper because it is negatively charged and copper is positively charged therefore they are attracted to each other.

Question 24

Which two things affect the amount of substance produced?

Answer 24

The size of current and the time the current passes through the electrolyte.

Question 25

During the electrolysis of sodium hydroxide, is sodium or hydrogen produced and why?

Answer 25

Hydrogen is produced because sodium is much higher up in the reactivity series therefore hydrogen is discharged in preference.

Question 26

If a current of 0.5A is passed for 1 hour and deposits 2.4g, how much mass would be deposited if the current was passed for 30 minutes?

Answer 26

1.2g