Chemical changes - Acids, alkalis and reactivity

Question 1

acid + base –

Answer 1

salt + water

Question 2

what is an acid

Answer 2

a substance that forms a H+ ions when dissolved in water

Question 3

what is a base

Answer 3

a substance that can neutralise an acid, producing a salt + water

Question 4

what is an alkali

Answer 4

a base that are soluble and that produce OH- ions when dissolved in water

Question 5

what is the reaction between a base and an acid called

Answer 5

neutralisation

Question 6

what is a strong acid

Answer 6

an acid that ionises completely in water into it’s H+ ions

Question 7

what is a weak acid

Answer 7

an acid that does not fully ionise in a solution, only a small proportion of acid particles dissociate to release H+ ions

Question 8

examples of strong acids

Answer 8

sulfuric, hydrochloric, nitric acids

Question 9

examples of weak acids

Answer 9

ethanoic, citric, carbonic acids

Question 10

what is the difference between strong and concentrated acids

Answer 10

acid strength tells you what proportion of the acid molecules ionise in water, whilst the concentration measures how much acid there is in a certain volume of water

Question 11

what does an acid + metal oxide give

Answer 11

salt + water

Question 12

what does an acid + metal hydroxide give

Answer 12

salt + water

Question 13

what does an acid + metal carbonate give

Answer 13

salt + water + carbon dioxide

Question 14

what does acid + metal give

Answer 14

salt + hydrogen

Question 15

examples of metals that do not react with water but react with dilute acids

Answer 15

magnesium, aluminium, zinc, iron and lead (iron and lead react slowly).

Question 16

metal + water

Answer 16

metal hydroxide + hydrogen

Question 17

how to separate metals in terms of reactivity

Answer 17

• see how they react with water
• potassium, sodium and lithium react very rapidly with water at room temperature
• calcium reacts quite rapidly
• magnesium, zinc, iron and copper do not react with water at room temperature

Question 18

why cant we react group 1 metals with dilute acids

Answer 18

because they would have a dangerously fast reaction with them

Question 19

how do certain metals react with dilute acids

Answer 19

calcium- extreme vigorous reaction magnesium - rapid reaction
zinc - quite rapid but slower but magnesium
iron - quite slow reaction
copper - no reaction

Question 20

what does the reactivity of a metal depend on

Answer 20

its ability to lose electrons and form a positive ion

Question 21

where are unreactive metals such as gold found

Answer 21

in the earth as a metal itself

Question 22

why is carbon used to displace elements from their compound

Answer 22

because metals higher in the reactivity series are more expensive and carbons cheappp

Question 23

describe a neutralisation reaction between an acid and an alkali

Answer 23

• acids produce H+ ion
• alkalis produce the OH- ion
• when they react, the hydrogen ions react with the hydroxide ions to produce water

H+ + OH- —-> H2O

Question 24

what do salts contain

Answer 24

• positive ion from the base or the alkali
• a negative ion which comes from the acid

Question 25

if an acid is weak, what direction does the arrow in the reaction go

Answer 25

both ways, its a reversible reaction

Question 26

what the relationship between pH and acid strength

Answer 26

stronger acids have a lower pH than weak acids for a given concentration - thats because strong acids fully ionise, producing a greater concentration of hydrogen ions than weaker acids

Question 27

as the pH scale decreases by one unit, how much does the concentration of hydrogen ions decrease by

Answer 27

10 times (one order of magnitude)

Question 28

what does the concentration of an acid tell us

Answer 28

the amount of acid molecules in a given volume of solution

Question 29

what is a dilute acid

Answer 29

one that has fewer acid molecules in a given volume