Electrolysis

Question 1

Definition of electrolysis

Answer 1

The passage of electricity through a chemical substance causing a chemical change and the formation of new substances at the electrodes

Question 2

for the bulb to light there must be?

Answer 2

a complete circuit

Question 3

Ionic substances dissolve in water to form what?

Answer 3

An aqueous solution

Question 4

The ions in the ionic substance become what>

Answer 4

Mobile

Question 5

if the aqueous solution is connected in a circuit what will happen?

Answer 5

an electric current will flow

Question 6

The aqueous solution is an example of what?

Answer 6

An electrolyte

Question 7

Give three examples of an aqueous solution

Answer 7

Sodium chloride solution
dilute sulphuric acid
copper sulphate solution

Question 8

electrolysis of sodium chloride solution observation at the anode (positive electrode)

Answer 8

fizzing and chlorine smell

Question 9

electrolysis of sodium chloride solution observation at the cathode (negative electode

Answer 9

hydrogen

Question 10

half equation for oxygen

Answer 10

4OH(-) - 4E- = 02 + 2H(2)0

Question 11

half equation for hydrogen

Answer 11

2H+ (+) 2E- = H2

Question 12

What are the ‘rules’ for the anode (positive electrode)

Answer 12

• halide ions always lose their electrons before hydroxide ions
• hydroxide ions will lose their electrons before sulphate or nitrate ect

Question 13

what are the ‘rules’ at the cathode?

Answer 13

metal ions below hydrogen in the reactivity series always gains electrons before H+ ions
-H+ ions always gain electrons before metal ions that are above it in the reactivity series

Question 14

Definition of the electrolysis of brine

Answer 14

a very important electrolysis of concentrated sodium chloride solution used in the industry

Question 15

what does the electrolysis of brine produce?

Answer 15

• Chlorine Gas
• Hydrogen Gas
• Sodium Hydroxide Solution

Question 16

What are the ions present in brine

Answer 16

Sodium
chlorine
hydroxide
hydrogen

Question 17

whats happens when an electrical current passes through brine at the cathode (-)

Answer 17

sodium and hydrogen ions move to the cathode
-H+ ions gain electrons and H+ gas is released
Na+ ions remain in solution

Question 18

What happens when an electrical current passes through brine at the Anode (+)

Answer 18

• chloride and hydroxide ions move to the anode
• chloride ions lose electrons and chlorine gas is released
• hydroxide ions remain in solution

Question 19

What is made in the electrolysis of brine and at which electrode or other>

Answer 19

• Hydrogen gas at the cathode
• Chlorine Gas at the anode
• sodium hydroxide solution left in the container

Question 20

What is Hyrogen Gas used for?

Answer 20

• harden veg oil into margarine

- make hydrochloric acid for use in pharmacy industry

Question 21

What is chlorine gas used for?

Answer 21

(poisonous) -to kill bacteria in drinking water and pools
- to make bleach + pvc/plastics
- to make disinfectant

Question 22

what is sodium hydroxide solution used for?

Answer 22

• soap
• paper
• bleach

Question 23

What is the test for hydrogen?

Answer 23

insert a lighted splint
gas burns with a pop
HAZARD- in air a spark causes explosion

Question 24

test for oxygen?

Answer 24

insert a glowing splint

the splint relights

Question 25

Test for carbon dioxide

Answer 25

- bubble the gas through limewater | - the limiter turns milky

Question 26

test for chlorine

Answer 26

- put damp BLUE litmus paper in the gas | - the litmus turns pink and then BLEACHES

Question 27

test for Ammonia

Answer 27

put red litmus in the gas -the litmus turns blue the gas is alkaline HAZARD= alkaline very soluble in water danger of suck back

Question 28

Hydrogen chloride test

Answer 28

put the gas ned to a bottle of ammonia solution | the gas gives dense white fumes of ammonium chloride

Question 29

test for water x2

Answer 29

add to anhydrous copper sulphate(white) add to blue cobalt chloride paper -anyhydrous copper sulphate turns blue blue cobalt chloride paper turns pink

Question 30

Test for pure water

Answer 30

boils at 100C | freezes at 0C

Question 31

test for Alkenes C=C double bonds (unsaturated hydrocarbons)

Answer 31

shake with bromine water | -bromine water decolourises turns from yellow/brown to colourless

Question 32

definition of an electrolyte

Answer 32

a liquid or gel which contains ions and can be decomposed by electrolysis, e.g. that present in a battery.

Question 33

definition of conductor

Answer 33

a metal that conducts electricity when it is solid as it does not have mobile ions

Question 34

In a circuit which way do the electrons go

Answer 34

negative to positive

Question 35

Why does solid Lead (II) not undergo electrolysis

Answer 35

It doesn't have mobile ions

Question 36

Describe what you would observe in the electrolysis of lead (II)

Answer 36

lead- a shiny substance would form at the cathode and bromine gas and fizzing would be given off at the anode