Topic 4 - Chemical changes

Question 1

What is an acid?

Answer 1

1. An acid is a substance that forms aqeuous solutions with a pH of less than 7
2. Acids form H+ ions in water

Question 2

What is a base?

Answer 2

A base is a substance with a pH greater than 7

Question 3

What is the reaction between acids and bases called?

Answer 3

Neutralisation

Question 4

What is an alkali?

Answer 4

1. An alkali is a base that dissolves in water to form a solution with a pH greater than 7
2. Alkalis form OH- ions in water

Question 5

What is the formula for a neutralisation reaction?

Answer 5

Acid + base –> salt + water

Question 6

Neutralisation reaction in terms of H+ ions and OH- ions?

Answer 6

H+ + OH- —> H2O

Question 7

Metal reacting with acid equation?

Answer 7

Metal + Acid —> Salt + Hydrogen

Question 8

Metal reacting with oxygen equation?

Answer 8

Metal + Oxygen —> Metal Oxide

Question 9

Metal reacting with water equation?

Answer 9

Metal + Water —> Metal Hydroxide + Hydrogen

Question 10

Metal reacting with steam?

Answer 10

Metal + Steam —> Metal oxide + Hydrogen

Question 11

Metal carbonate reacting with acid?

Answer 11

Metal Carbonate + Acid —> Salt + Water + Carbon dioxide

Question 12

What is tritration used for?

Answer 12

1. To find out concentrations
2. Titrations allow you to find out exactly how much acid is needed to neutralise a quantity of alkali, or vice versa

Question 13

What is the burette filled with in titration?

Answer 13

1. Solution of known concentration
2. If it is an unknown acid, the burette is filled with an alkali
3. If it is an unknown alkali, the burette is filled with an acid

Question 14

What is the pipette filled with in titration?

Answer 14

Solution of unknown concentration

Question 15

What is the titration method?

Answer 15

0. This is to find the conentration of an unknown alkali
1. Using a pipette and pipette filler, add a set volume of the alkali to a conical flask. Add 2 or 3 drops of indicator
2. Use a funnel to fill a burette with some acid of known concentration (below eye level). Record the initial volume of the acid
3. Using the burette, add the acid to the alkali drop by drop and give the concial flask a swirl
4. The indicator changes colour when all of the alkali has been neutralised
5. Record the final volume of acid in the burette and use it, along with the intial reading, to calculate the volume of acid needed to neutralise the alkali

Question 16

What colours are methyl orange in acids and alkalis?

Answer 16

1. Red in acid
2. Yellow in alkali

Question 17

What colours are phenolphthalein in acids and alkalis?

Answer 17

1. Colourless in acis
2. Pink in alkalis

Question 18

What do acids do in aqeuous solutions?

Answer 18

1. They ionise
2. They produce H+ ion (hydrogen ions)

Question 19

What are strong acids?

Answer 19

1. Strong acids are acids that ionise completely in water
2. All acid particles dissociate to release H+ ions

Question 20

What are weak acids?

Answer 20

1. Weak acids are acids that do not fully ionise in water, only partially
2. Only a small proportion of acid particles dissociate to release H + ions

Question 21

The the ionisation of a weak acid irreversible or reversible?

Answer 21

Reversible

Question 22

The the ionisation of a strong acid irreversible or reversible?

Answer 22

Irreversible

Question 23

How does pH and concentration of H+ ions link?

Answer 23

1. For ever decrease of 1 on the pH scale, the concentration of H+ ions increases by a factor of 10
2. So, an acid that has a pH of 4 has 10 times the cocentration of H+ ions of an acid that has a pH of 5

Question 24

What is the concentration of an acid?

Answer 24

The concentration of an acid is how much acid there is in a certain volume of water

Question 25

What is reduction in terms of oxygen?

Answer 25

Loss of oxygen

Question 26

What is oxidation in terms of oxygen?

Answer 26

Gain of oxygen

Question 27

How can some metals be extracted from their ores by reduction with carbon?

Answer 27

1. Metals can be extracted from their ores by reduction with carbon when the metal is less reactive than carbon 2. Carbon is used as the reducing agent - it reacts with the oxygen in the metal oxide 3. This means that carbon is oxidised and the ore is reduced

Question 28

What is reduction in terms of electrons?

Answer 28

Gaining electrons

Question 29

What is oxidiation in terms of electrons?

Answer 29

Losing electrons

Question 30

What happens in redox reactions?

Answer 30

In redox reactions, reduction and oxidation of electrons happens at the same time

Question 31

What type of reaction are displacement reactions?

Answer 31

Redox reaction

Question 32

What is a displacement reaction?

Answer 32

A more reactive metal displacing a less reactive metal in its compound