C6 Electrolysis Papers Part 2

Question 1

What is the Reaction to produce iron from iron oxide

Answer 1

Carbothermal reduction

Question 2

Why electrically conductive aluminium is used to make cans

Answer 2

Low density

Less resistance to corrosion

Question 3

Why the positive electrode must be continually replaced

Answer 3

Electrode reacts with oxygen

Question 4

Calculate the mass of oxygen produced when 2000 kg of aluminium oxide is completely electrolysed

Answer 4

2 Mr of Al2O3 = 204

204 (kg of Al2O3) gives 96 kg of O2

(2000 ➗ 204) x 96 = 941kg

Question 5

Why sodium chloride solution can’t be used as the electrolyte to produce sodium metal

Answer 5

Hydrogen would be produced instead of sodium as sodium is more reactive than hydrogen

Question 6

Calculate the volume of 150 kg of chlorine gas at room temperature and pressure

The volume of one mole of any gas at room temperature and pressure is 24.0 dm3

Relative formula mass (M.): Cl = 71

Answer 6

150,000
_________ x 24 = 50,704dm3 so 50,700dm3

 71

Question 7

Which line in figure 3 shows volume of gas collected is directly proportional to time

Answer 7

Hydrogen line only

Question 8

Why can graphite conduct electricity

Answer 8

Has delocalised electrons

Question 9

What is produced at cathode/anode molten zinc chloride

Answer 9

Cathode - zinc as zinc is more reactive than hydrogen

Anode - chlorine as it is halide so chlorine is produced not oxygen

Question 10

What is produced at cathode/anode potassium bromide

Answer 10

Cathode - hydrogen as potassium is more reactive than hydrogen

Anode - bromine as it is halide

Question 11

Why wouldn’t electrolysis work if was solid sodium chloride

Answer 11

Solid zinc chloride does not conduct electricity as ions cannot move in solid

Question 12

How graphite conducts electricity answer in terms of structure and bonding in graphite

Answer 12

Each carbon atoms forms 3 covalent bonds

1 electron per carbon atom is delocalised

So these electrons carry charge through the graphite

Question 13

The student made an error in selecting the apparatus for this investigation

How should the apparatus be changed

Give one reason for your answer

Answer 13

Use measuring cylinders instead of test tubes as test tubes can’t measure volume

Question 14

Describe trends in results above of hydrogen and chlorine increasing graph

Answer 14

Volume of hydrogen collected is directly proportional to time

Rate of collection of hydrogen is 0.45 cm/min

Up to 8 minutes chlorine is collected at increasing rate

Question 15

No gas escapes from the apparatus

Suggest one reason for the difference in volume of each gas collected

Answer 15

Chlorine reacts with water

Question 16

Calculate the amount in moles of chlorine collected after 20 minutes

Use Figure 3

The volume of one mole of any gas at room temperature and pressure is 24.0 dm

Answer 16

6.6 ➗ 1000 = 0.0066

0.0066 ➗ 24 = 2.75 x 10^ -4

Question 17

Independant variable

Answer 17

The variable that changes during an experiment

Question 18

Dependant variable

Answer 18

Variable being tested or measured

Question 19

Control variable

Answer 19

Variable that is kept the same during scientific experiment

Question 20

Independant variable for electrolysing salt solutions with inert electrodes

Answer 20

Salt solutions

Question 21

Observation for electrolysing salt solutions with inert electrodes

Answer 21

Solid/metal deposit on negative electrode

Question 22

Why the product at negative electrode is not always a metal

Answer 22

Hydrogen produced when metal is more reactive than hydrogen

Question 23

Why does iodine have higher boiling point than chlorine

Answer 23

Forces between iodine atoms are stronger

Question 24

Predict the boiling point of bromine

Answer 24

Anything in range +30 to +120

Question 25

Trend in boiling point group 1 and halogens

Answer 25

Group 1 - decreases as goes down group Halogens - increases as goes down group

Question 26

Why trend in reactivity decreases halogens as go down group

Answer 26

Atomic mass of the halogens increases Increase in electron shells Atoms get larger as go down group Attraction to outer electron from nucleus decreases

Question 27

Why trend in reactivity increases group 1 as go down group

Answer 27

Atoms become larger Outer electron becomes further from the nucleus Attraction between nucleus and outer electron gets weaker so electron is more easily lost

Question 28

Why trend in boiling point increase down group 7

Answer 28

Atoms increase in size as they gain extra electron shells Intermolecular forces become stronger More energy is required to break these forces

Question 29

Why trend in boiling point decrease down group 1

Answer 29

Additional shell being added to the previous element causes atomic radius to increase The increasing atomic radius means weaker forces between atoms so lower melting and boiling point

Question 30

What colour is final solution of reaction chlorine added to potassium iodide solution

Answer 30

Brown

Question 31

REACTIVITY SERIES

Answer 31

Potassium Sodium Lithium Calcium Magnesium Aluminium CARBON Zinc Iron Tin Lead HYDROGEN Copper Silver Gold Platinum

Question 32

Ionic equation for reaction of chlorine with potassium iodide

Answer 32

2I- + Cl2 ---------> I2 + 2Cl-

Question 33

Why is potassium not included in Ionic equation for reaction of chlorine with potassium iodide

Answer 33

It is a spectator ion and dissociates in aqueous solution Potassium ions do not undergo any chemical change during reaction and don't affect redox process therefore excluded from net ionic equation

Question 34

Spectator ion

Answer 34

Ions that are present in the reaction mixture but don't participate in the chemical reaction They remain unchanged throughout the process

Question 35

Why potassium iodide conducts electricity

Answer 35

Contains ions which can move

Question 36

Transition metals ions

Answer 36

+2

Question 37

Which electrode does oxidation happen in

Answer 37

Positive anode

Question 38

Which electrode does reduction happen in

Answer 38

Negative cathode

Question 39

Why zinc ions move towards negative electrode

Answer 39

Zinc ions are positive and opposite charges attract

Question 40

What type of reaction occurs when the zinc ions gain electrons

Answer 40

Reduction

Question 41

Why alloy is harder than pure zinc

Answer 41

Different sized atoms No layers or rows so can't slide

Question 42

Alloys can be bent. Some alloys return to their original shape when heated What name is used for these alloys

Answer 42

Shape memory

Question 43

What happens when a magnesium atom reacts with chlorine atoms to produce magnesium chloride.

Answer 43

Magnesium loses 2 electrons and chlorine gains 1 electron Forms ionic bonds Electrostatic attraction between ions 8 electrons in outer shell

Question 44

Why magnsium chloride must be molten or dissolved in water to be electrolysed

Answer 44

Ions can move to electrodes and carry charge

Question 45

How magnsium is produced at negative electrode

Answer 45

Magnesium ions attracted to electrode so magnsium ion gains 2 electrons

Question 46

Why magnesium is not produced at negative electrode

Answer 46

Magnesium is more reactive than hydrogen

Question 47

Complete and balance the half equation for the reaction at the positive electrode. _______ Cl- ----------> Cl2 + _________

Answer 47

2Cl- -------> Cl2 + 2e-

Question 48

Why metals can be bent and shaped

Answer 48

Layers of particles can slide