3.1.12 Acids and Bases

Question 1

Define an acid

Answer 1

Proton Donor

Question 2

Define a base

Answer 2

Proton Acceptor

Question 3

Define a strong Acid

Answer 3

An acid (proton donor) which fully dissociates

Question 4

Define a weak Acid

Answer 4

An acid ( proton donor) which only partially dissociates

Question 5

Define pH

Answer 5

pH = -Log10[H+]

Question 6

[H+] =

Answer 6

[H+] = 10-pH

Question 7

Ionic Product of Water (Kw) =

Answer 7

Kw = [H+][OH-]

Question 8

When calculating the pH of a strong acid use:

Answer 8

pH = -Log10[H+]

Question 9

When calculating the pH of a strong base use:

Answer 9

Rearrange Kw = [H+][OH-] to get [OH-] then use pH = -Log10[H+]

Question 10

When calculating the pH of a weak acid use:

Answer 10

Ka = [H+]2/[HA] and rearrange to get [H+]
then use pH = -Log10[H+]

Question 11

When calculating the pH of a buffer use:

Answer 11

Ka = [H+][A-]/ [HA] and rearrange to get [H+] then use pH = -Log10[H+]

Question 12

Chemical equation for Hydrochloric Acid + Sodium

Answer 12

HCl(aq) + Na(s) –> NaCl(aq) + ½ H2(g)

Question 13

Chemical equation for Nitric Acid + Potassium Oxide

Answer 13

2HNO3 (aq) + K2O(s) –> 2KNO3 (aq) + H2O(l)

Question 14

Chemical equation for Phosphoric Acid + Sodium Hydroxide

Answer 14

H3PO4(aq) + 3NaOH(s) –> Na3PO4(aq (aq) + 3H2O(l)

Question 15

Chemical equation for Hydrochloric Acid + Calcium Oxide

Answer 15

2HCl (aq) + CaO(s) –> CaCl2 (aq) + H2O(l)

Question 16

Chemical equation for Sulfuric Acid + Sodium Carbonate

Answer 16

H2SO4(aq) + Na2CO3(s) –> Na2SO4(aq) + CO2(g) + H2O(l)

Question 17

Na2O(s) + H2O(l) –> products and pH

Answer 17

2Na+(aq) + 2-OH(aq) pH 13-14

Question 18

MgO(s) + H2O(l) –> products and pH

Answer 18

Mg(OH)2(aq) pH 9-10

Question 19

P4O10(s) + 6H2O(l) –> products and pH

Answer 19

4H3PO4(aq) pH 0-1

Question 20

SO2(g) + H2O(l) –> products and pH

Answer 20

H2SO3(aq) pH 2-3

Question 21

SO3(g) + H2O(l) –> products and pH

Answer 21

H2SO4(aq) pH 0-1

Question 22

A difference of 1 on the pH scale means

Answer 22

a 10x difference in [H+]

Question 23

pKa =

Answer 23

-Log10Ka

Question 24

Ka =

Answer 24

10-pKa

Question 25

The value of Kw will alter with temperature, explain why pure water is always neutral

Answer 25

because [H+] = [-OH] at all times.

Question 26

Define a buffer

Answer 26

A BUFFER is a solution which can resist changes in pH when a small amount of acid or base is added

Question 27

What is an acid buffer made of

Answer 27

An ACIDIC BUFFER is made of a weak acid and a soluble salt of that acid. It maintains a pH below 7.

Question 28

What is a basic buffer made of

Answer 28

A BASIC BUFFER is made of a weak BASE and a soluble salt of that BASE. It maintains a pH above 7.

Question 29

Steps to get to pH in a buffer calculation when given concentration of weak acid CH3COOH, concentration of the salt CH3COONa and Ka value for weak acid.

Answer 29

sub values straight into Ka = [H+][ CH3COO]/[CH3COOH]. Rearrange to get [H+] Use pH = -Log10[H+]

Question 30

Steps to get to pH in a buffer calculation when given volume and conc of both the weak acid and a base, where the weak acid is in excess, Ka value also given

Answer 30

Complete ICE box Find new moles of acid and the moles of the salt produced. sub mole* values into Ka = [H+][CH3COO]/[CH3COOH]. *volumes would cancel out so moles can be used instead of conc Rearrange to get [H+] Use pH = -Log10[H+]

Question 31

Steps to get to pH in a buffer calculation when enough base has been added to neutralise exactly half of the acid present.

Answer 31

Recognise this is a special situation - half neutralisation point so Ka = [H+] Use pH = -Log10[H+]

Question 32

Formula for sulphuric acid

Answer 32

H2SO4

Question 33

Formula for nitric acid

Answer 33

HNO3

Question 34

Formula for phosphoric acid

Answer 34

H3PO4

Question 35

Formula for ethanoic acid

Answer 35

CH3COOH

Question 36

Formula for aluminium phosphate

Answer 36

AlPO4

Question 37

Formula for sodium ethanoate

Answer 37

CH3COONa

Question 38

Formula for lead (II) nitrate

Answer 38

Pb(NO3)2

Question 39

Formula for potassium sulphate

Answer 39

K2SO4

Question 40

Formula for magnesium chloride

Answer 40

MgCl2

Question 41

Explain how to chose a suitable indicator for a titration

Answer 41

A SUITABLE INDIATOR CHANGES COLOUR SOMEWHERE ON THE VERTICAL SECTION OF A pH TITRATION CURVE

Question 42

Define half neutralisation point

Answer 42

‘The point at which enough base has been added to neutralise exactly half of the acid’

Question 43

What does the vertical section of a titration curve show?

Answer 43

This indicates what the average titre would be which can be used in a calculation. The midpoint of this vertical section is the equivalence point.