CC8 - Acids And Alkalis

Question 1

what is the PH scale

Answer 1

a measure of how acidic or alkaline a substance is

Question 2

what is the PH of a neutral substance

Answer 2

7

Question 3

what are acids

Answer 3

• a substance with a PH less than 7
• forms H+ ions in water

Question 4

explain the strength of an acid in terms of H+ ions

Answer 4

• stronger acids have a higher concentration of H+ ions
• as the concentration of H+ ions increases, the PH of the acid decreases

Question 5

what is a base

Answer 5

a substance that reacts with an acid to produce salt and water only

Question 6

what is an alkali

Answer 6

• a base that is soluble in water
• have PH greater than 7
• form OH- ions in water (hydroxide ions)

Question 7

explain the strength of an alkali in terms of OH- ions

Answer 7

• stronger alkalis have a greater concentration of OH- ions
• as the concentration of OH- ions increases, the PH of the alkali increases

Question 8

what is an idicator

Answer 8

a dye that changes colour depending on whether the PH of a substance is above or below a certain PH

Question 9

colours of universal indicator in: acids, neutral, alkalis

Answer 9

acid: strong = red, weak = yellow
neutral: green
alkali: strong = purple, weak = blue

Question 10

colours of litmus indicator in: acids, neutral, alkalis

Answer 10

acid: red
neutral: purple
alkali: blue

Question 11

colours of methyl orange indicator in: acids, neutral, alkalis

Answer 11

acid: red
neutral: yellow
alkali: yellow

Question 12

colours of phenolphthalein indicator in: acids, neutral, alkalis

Answer 12

acid: colourless
neutral: colourless
alkali: pink

Question 13

what is the reaction between an acid and a base called

Answer 13

neutralisation

Question 14

neutralisation rection formula

Answer 14

acid + base —–> salt + water

Question 15

ionic equation of neutralisation reactions in aqueous solutions

Answer 15

H+ + OH- —–> H20

Question 16

what is the PH of the products of a neutralisation reaction, why

Answer 16

PH 7
- the concentration of H+ and OH- ions is equal

Question 17

test for carbon dioxide

Answer 17

test - bubble the gas through limewater
result - if CO2 is present, the limewater will turn cloudy

Question 18

test for hydrogen

Answer 18

test - hold a lit splint to the gas
result - if hydrogen is present, there will be a ‘squeaky pop’

Question 19

what can all acids do in a solution

Answer 19

• dissociate (ionise)

Question 20

what does it mean when an acid dissociates

Answer 20

the acid splits up to produce a hydrogen ion and another ion

Question 21

what is a strong acid

Answer 21

• when all of the molecules split to form H+ ions
• fully dissociated

Question 22

what is a weak acid

Answer 22

• when only some of the molecules split to form H+ ions
• partially dissociated

Question 23

what is special about the ionisation of weak acids

Answer 23

the reaction is reversible
- equilibrium lies to the left as only some molecules release H+ ions

Question 24

what is a dilute acid

Answer 24

when there is a small proportion of acid molecules compare to the volume of water per g dm-3
- strong acids can be dilute as concentration is the number of dissolved acid molecules not the number of molecules that have dissociated to produce H+ ions

Question 25

what is a concentrated acid

Answer 25

when there is a large proportion of acid molecules compare to the volume of water per g dm-3
- weak acids can be concentrated as concentration is the number of dissolved acid molecules not the number of molecules that have dissociated to produce H+ ions

Question 26

about salts

Answer 26

• formed during neutralisation reactions
• ionic compunds

Question 27

what salts do hydrochlorid acid, sulfuric acid and nitric acid generally produce

Answer 27

hydrochloric acid: chloride salts
sulfuric acid: sulfate salts
nitric acids: nitrate salts

Question 28

word formula for the reaction between: acid and metal oxide

Answer 28

acid + metal oxide —–> salt + water

Question 29

word formula for the reaction between: acid and metal hydroxide

Answer 29

acid + metal hydroxide —–> salt + water

Question 30

word formula for the reaction between: acid and metal

Answer 30

acid + metal —–> salt + hydrogen

Question 31

word formula for the reaction between: acid and metal carbonate

Answer 31

acid + metal carbonate —–> salt + water + carbon dioxide

Question 32

where does the noise of the ‘squeaky pop’ come from in a test for hydrogen

Answer 32

the hydrogen burning with oxygen in the air to form water

Question 33

what happens to the PH if the concentration of H+ ions increases by factor 10

Answer 33

PH decreases by 1 (stronger acid)
- for each addition factor of 10 the H+ ions increases by the PH decrease 1 more
eg. factor 100 = PH decreases by 2

Question 34

what happens to the PH if the concentration of H+ ions decreases by factor 10

Answer 34

PH increases by 1 (weaker acid)
- for each addition factor of 10 the H+ ions decrease by the PH increases 1 more
eg. factor 100 = PH increases by 2

Question 35

what does how you make a salt depend on

Answer 35

whether it is soluble or insoluble

Question 36

what do soluble and insoluble salts form when two solutions are mixed

Answer 36

• soluble salts: in solution
• insoluble salts: a precipitate

Question 37

are common salts of sodium, potassium and ammonium soluble or insoluble

Answer 37

soluble

Question 38

are nitrates soluble or insoluble

Answer 38

soluble

Question 39

are common chlorides soluble or insoluble

Answer 39

soluble except: silver chloride and lead chloride

Question 40

are common sulfates soluble or insoluble

Answer 40

soluble except: lead sulfate, barium sulfate and calcium sulfate

Question 41

are common carbonates and hydroxides soluble or insoluble

Answer 41

insoluble except: sodium, potassium and ammonium ones

Question 42

how to make a pure dry sample of an insoluble salt

Answer 42

• precipitation reaction
• react the right two soluble salts together