Acids & Bases

Question 1

what is the definition of an acid

Answer 1

an acid is a substance that produces hydrogen ions when dissolved in water

Question 2

what is the definition of an alkali

Answer 2

an alkali is a substance that produces hydroxide ions when dissolved in water

Question 3

what are the common acids

Answer 3

HCl
HNO3
H2SO4
H3PO4
CH3COOH

Question 4

what are the common alkalis

Answer 4

KOH
NaOH
Ca(OH)2
NH3 or NH4OH

Question 5

what is the definition of a base

Answer 5

bases are metal oxides or hydroxide that react with acids to form salt and water only (neutralisation)

Question 6

are alkalis insoluble or soluble bases

Answer 6

alkalis are soluble metal oxides and hydroxides

Question 7

define basicity of acids

Answer 7

no. of moles produced when 1 mole of acid dissolves in water

Question 8

what are the 3 basicities of acids and examples of them

Answer 8

monobasic: HCl
dibasic: H2SO4
tribasic: H3PO4

Question 9

what is the concentration of H+ ions in 1mol/dm3 HNO3

Answer 9

1mol/dm3

Question 10

what is the concentration of H+ ions in 1 mol/dm3 H2SO4

Answer 10

2mol/dm3

Question 11

does the strength of acids/alkalis depend on the concentration of H+/OH- ions

Answer 11

no

strength does not depend on concentration

Question 12

define strong acid
what is the pH
list 3 examples

Answer 12

completely ionised when dissolved in water to produce hydrogen ions

pH = 1-2

HCl
H2SO4
HNO3

Question 13

define weak acid
what is the pH
list 3 examples

Answer 13

partially ionised when dissolved in water to produce hydrogen ions

pH = 3-6

CH3COOH
citric acid
carbonic acid

Question 14

define strong alkali
what is the pH
list 3 examples

Answer 14

completely ionised when dissolved in water to produce hydroxide ions

pH = 13-14

NaOH
KOH
Ca(OH)2

Question 15

define weak alkali
what is the pH
list 1 example

Answer 15

partially ionised when dissolved in water to produce hydroxide ions

pH = 12

NH3

Question 16

methyl orange:
at what pH does the colour change
what is the colour change

Answer 16

pH4

red –> yellow

Question 17

screened methyl orange:
at what pH does the colour change
what is the colour change

Answer 17

pH4

violet –> green

Question 18

phenolphthalein:
at what pH does the colour change
what is the colour change

Answer 18

pH9

colourless –> pink

Question 19

what are 2 causes of acidic soil

Answer 19

acid rain,

extensive use of fertilisers (e.g. ammonium sulphate)

Question 20

what are 3 substances that can neutralise acidic soil

Answer 20

Ca(OH)2, CaO, CaCO3

calcium hydroxide, calcium oxide, calciul carbonate

Question 21

why can’t metals be used to neutralise acidic soil

Answer 21

acid + metal –> salt + H2

highly flammable hydrogen gas will be produced

Question 22

what are the 4 types of oxides

Answer 22

neutral, acidic, basic, amphoteric

Question 23

define neutral oxides

list 3 examples

Answer 23

non-metallic oxides that do not react with acids or bases

NO
H2O
CO

Question 24

define acidic oxides

Answer 24

non-metallic oxides that react with water to form acids

• can cause acid rain
• < pH 7

e.g. SO2, SO3, CO2, NO3

Question 25

define basic oxides

Answer 25

metallic oxides that react with water to form alkalis

• react with acids to produce salt + water
• oxides of metals

e.g. K2O, Na2O, CaO

Question 26

define amphoteric oxides

list 4 examples

Answer 26

metallic oxides that can act as basic or acidic oxides
- react with either to form salt

ZnO
Al2O3
PbO
SnO