Chemistry Past Paper Corrections

Question 1

What metal is used for galvanising?

Answer 1

Zinc

Question 2

Methods to prevent rusting

Answer 2

Greasing, Oiling, Painting, Galvanising.

Question 3

Test for ammonium ions

Answer 3

Add sodium hydroxide solution & warm. Test gas with damp red litmus paper. Damp red litmus paper turns blue.

Question 4

Hazards of hydrochloric acid & prevention

Answer 4

Corrosive & burns skin, use fume cupboard & wear safety goggles for eye protection.

Question 5

Electron configuration when sodium oxide forms

Answer 5

Each atom of sodium transfers one electron to the oxygen atom. Each sodium atom loses one electron & oxygen gains 2 electrons.

Question 6

Explain why water has a lower melting point than sodium oxide

Answer 6

The intermolecular forces of attraction between water molecules are weaker than the attractions between ions. Ionic bonds need a lot of energy to break.

Question 7

Final colour of litmus paper in methylbenzene solution

Answer 7

Blue because there are no hydrogen ions.

Question 8

How to make fair tests for displacement reactions

Answer 8

Same initial temperature, mass & surface area of metal added, concentration of metal salt solution.

Question 9

Why is calcium not used in displacement reactions?

Answer 9

Calcium is too reactive & would react with water.

Question 10

Uses of ammonium nitrate

Answer 10

Fertilizers

Question 11

Why is solid in excess

Answer 11

To completely neutralise the acid

Question 12

Why are metals ductile?

Answer 12

Layers of ions slide over each other.

Question 13

Why is a reaction exothermic?

Answer 13

More energy is released in making bonds than absorbed in breaking bonds.

Question 14

Why is universal indicator better than methyl orange?

Answer 14

It indicates pH as there is more than one colour in acid & shows how acidic the water is.

Question 15

Methyl orange colour in acid

Answer 15

Red

Question 16

Methyl orange colour in alkali

Answer 16

Yellow

Question 17

Safety precaution & reason when working with fire

Answer 17

Tie hair back as it might catch fire

Question 18

Definition of relative atomic mass

Answer 18

The average mass of an atom of an element relative to 1/12th the mass of an atom of carbon-12.

Question 19

Changes that occur during formation of poly(ethene)

Answer 19

One of the bonds in the double bond breaks & many monomers join together to form a chain.

Question 20

Flame test

Answer 20

Use a clean platinum/nichrome wire to put solid over a roaring bunsen burner flame.

Question 21

Which negative ion cannot be identified by precipitation reaction?

Answer 21

Nitrate / NO3 -

Question 22

Why does hot water evaporate more quickly than cold water?

Answer 22

Particles have more energy to overcome the forces between water molecules.

Question 23

Formula of ammonium ion

Answer 23

NH4 +

Question 24

What happens when calcium reacts with chlorine? (in electrons terms)

Answer 24

Calcium loses electrons & chlorine gains electrons. Two atoms of chlorine each gain one electron.

Question 25

How to make ions conduct electricity?

Answer 25

Heat solid ionic compound until it melts

Question 26

What temperature for cracking?

Answer 26

600 - 700 degree celsius

Question 27

Explain how barrier method prevents rusting

Answer 27

Coating iron in paint/oil/grease which stops oxygen & water getting to the iron.

Question 28

What happens with protons in a neutralisation reaction?

Answer 28

Acid donates protons, base accepts protons

Question 29

How does the melting point change with impurity?

Answer 29

The impure substance will melt over a range of temperatures

Question 30

Describe method to prove that manganese (IV) oxide is catalyst

Answer 30

Filter out manganese oxide & leave to dry. Mass is the same.

Question 31

Why do isotopes have the same chemical properties?

Answer 31

Same electron configuration

Question 32

How does increasing surface area increase rate of reaction?

Answer 32

Greater surface area so more frequent collisions

Question 33

Two conditions kept the same for chromatography

Answer 33

Same solvent & type of chromatography paper.

Question 34

How does magnesium oxide show it contains metal?

Answer 34

Is a base

Question 35

Thermal decomposition definition

Answer 35

Breaking down of a substance by heating.

Question 36

Problem caused by addition polymer disposal

Answer 36

Toxic gases & greenhouse gases are produced when burned

Question 37

Prepare dry, pure silver nitrate crystals

Answer 37

Heat to evaporate some of the water. Leave to cool to crystallise & filter to obtain crystals. Dry using paper towel.

Question 38

Diamond type

Answer 38

Giant covalent structure

Question 39

Graphite type

Answer 39

Giant covalent

Question 40

C60 Fullerene type

Answer 40

Simple molecular structure

Question 41

Carbon dioxide type

Answer 41

Simple molecular structure

Question 42

Silicon dioxide type

Answer 42

Giant covalent structure

Question 43

How to increase percentage yield of water

Answer 43

Stand the measuring cylinder in a beaker of ice so less water vapour lost.

Question 44

Why is it not important to add exact volume of acid?

Answer 44

The acid is in excess therefore a precise measurement of volume is not required.

Question 45

Universal indicator colour in acid

Answer 45

Red

Question 46

Universal indicator colour in alkali

Answer 46

Purple

Question 47

Bromine colour

Answer 47

Orange

Question 48

Iodine colour

Answer 48

Brown

Question 49

Why is excess necessary?

Answer 49

To make sure all acid reacts so that a pure solution is obtained.

Question 50

Why is carbon dioxide extinghuisher not good for magnesium fire?

Answer 50

Fire would keep burning & large amount of thermal energy would be released.

Question 51

Ammonium chloride formation change of state

Answer 51

Sublimation

Question 52

What does displayed formula show?

Answer 52

All atoms & all bonds

Question 53

Phenolphthalein acid colour

Answer 53

Colourless

Question 54

Phenolphthalein alkali colour

Answer 54

Pink

Question 55

What determines period of elements?

Answer 55

Number of shells

Question 56

Why may results be inaccurate at too high temperatures?

Answer 56

Solution would not remain at required temperature

Question 57

Advantage of lid

Answer 57

Stop solid being lost

Question 58

First step in preparing pure crystals when not yet reacted?

Answer 58

Warm to react solutions

Question 59

Purpose of condenser

Answer 59

Steam is cooled and condenses

Question 60

Water and group 1 metal products

Answer 60

Metal hydroxide & hydrogen

Question 61

Ion structure

Answer 61

Giant ionic lattice

Question 62

Why not react sulfuric acid with marble chips?

Answer 62

Insoluble calcium sulfate will form which will form a coating on the marble chips slowing down the reaction.

Question 63

Why is hydrogen passed through lead tube while cooling?

Answer 63

So that the hot lead does not react with oxygen converting back to lead oxide