C4 - Chemical Changes

Question 1

What is an acid?

Answer 1

it releases H+ (hydrogen) ions in water and turns universal indicator red - yellow

Question 2

What is an alkali?

Answer 2

it releases OH- (hydroxide) ions in water and turns universal indicator blue - purple

Question 3

metal + acid –>

Answer 3

salt + hydrogen

Question 4

acid + alkali –>

Answer 4

salt + water

Question 5

acid + carbonate –>

Answer 5

salt + water + carbon dioxide

Question 6

What is the salt ending for hydrochloric acid?

Answer 6

chloride

Question 7

What is the salt ending for sulfuric acid?

Answer 7

sulfate

Question 8

What is the salt ending for nitric acid?

Answer 8

nitrate

Question 9

When it ends in hydroxide, this means it’s …

Answer 9

an alkali

Question 10

How do you test if a metal + acid reaction is successful?

Answer 10

Hydrogen test - lit splint, squeaky pop if positive

Question 11

How do you test if an acid + alkali reaction is successful?

Answer 11

Universal indicator, turns green if positive

Question 12

How do you test if an acid + carbonate reaction is successful?

Answer 12

Carbon dioxide test - lime water, turns cloudy if positive

Question 13

Define independent variable

Answer 13

the thing you change in the experiment

Question 14

Define dependent variable

Answer 14

the thing you measure

Question 15

Define control variables

Answer 15

the things you keep the same (to ensure a fair test)

Question 16

Define a strong acid

Answer 16

they fully ionise in water

Question 17

Define a weak acid

Answer 17

they partially ionise in water

Question 18

Describe a method a student could use to make pure dry crystals of salt from metal oxide and acid (6 marks)

Answer 18

• put 50 ml of (specific) acid in a beaker
• add excess amount of (metal) oxide to acid
• heat mixture using bunsen burner and stir
• filter mixture with funnel and filter paper to remove excess (metal) oxide
• heat (specific mixture) solution using a bunsen burner, evaporating basin and water bath for 10 mins
• leave to cool and crystallise

Question 19

What is the ionic equation for neutralisation?

Answer 19

H+ + OH- –> H₂O

Question 20

What colour does methyl orange turn for acid and alkali?

Answer 20

acid = red
alkali = yellow

Question 21

What does a burette measure?

Answer 21

a burette is used to accurately measure a variable (unknown) volume drop by drop

Question 22

What does a pipette measure?

Answer 22

a pipette measures a fixed volume

Question 23

How do you do a titration calculation question?

Answer 23

• make a table for acid and alkali with n, c and v
• fill in what the question tells you (3 things)
• convert all volumes into dm³
• calculate the moles of the side you can - n = c x v
• use the molar ratio from the equation to find the other moles
• calculate the last missing space c = n/v
• to convert to g/dm³, times the answer by it’s relative formula mass

Question 24

Define a dilute solution

Answer 24

small number of acid molecules per volume

Question 25

Define a concentrated solution

Answer 25

large number of acid molecules per volume

Question 26

Why can't universal indicator be used during a titration experiment?

Answer 26

It doesn't have a sudden change so end point is hard to determine

Question 27

Define a displacement reaction

Answer 27

the metal in a compound is displaced by a more reactive metal to form a new compound

Question 28

Define reduced (in terms of oxygen)

Answer 28

oxygen removed

Question 29

Define oxidised (in terms of oxygen)

Answer 29

oxygen gained

Question 30

Define electrolysis

Answer 30

electrolysis uses electricity to split ionic compounds

Question 31

What happens at the cathode of a molten electrolysis?

Answer 31

- (metal) ion is attracted to the negative cathode - (metal) ion gains (amount of positive charge it has) electrons to form a neutral atom - (metal) has been reduced

Question 32

What happens at the anode of a molten electrolysis?

Answer 32

- (non-metal) ion is attracted to the positive anode - (non-metal) ion loses (amount of negative charge it has) electrons to form a neutral atom - (non-metal) has been oxidised - 2 atoms join to form a diatomic molecule

Question 33

Describe an electrolysis diagram

Answer 33

There's a cell with two electrodes - anode (+) and cathode (-). At the anode, there are anions which are negative non-metal ions and at the cathode, there are cations which are positive metal ions.

Question 34

Define oxidation (in terms of electrons)

Answer 34

loss of electrons

Question 35

Define reduction (in terms of electrons)

Answer 35

gain of electrons

Question 36

What does the half equation look like at the negative electrode?

Answer 36

metal ion + electrons --> metal - the amount of positive charge the ion has is the number of electrons

Question 37

What does the half equation look like at the positive electrode?

Answer 37

non-metal ion --> electrons + non-metal (diatomic molecule) - the amount of negative charge has to balance out as well as the number of molecules

Question 38

Why does the ionic compound have to be molten/in solution for electrolysis?

Answer 38

so the ions can flow through the structure

Question 39

Why is cryolite used in electrolysis?

Answer 39

It lowers the the melting point so it uses less energy to make molten.

Question 40

Why does the positive electrode need to be replaced regularly (in aqeous electrolysis) ?

Answer 40

It is made of carbon which reacts with the oxygen produced at the anode to make carbon dioxide.

Question 41

What are the two rules for electrolysis of an aqueous solution?

Answer 41

- at the negative electrode, the least reactive between hydrogen and the metal in the compound will form - at the positive electrode, if it's group 7 then it will be formed but if not, oxygen will form

Question 42

What are the two extra ions involved in aqueous electrolysis?

Answer 42

H+ and OH- (because it was dissolved in water)