Acids and bases

Question 1

What is meant by a Bronsted-Lowry acid?

Answer 1

Proton donor

Question 2

What is meant by a Bronsted-Lowry base?

Answer 2

Proton acceptor

Question 3

What is meant by a strong acid?

Answer 3

Fully dissociates

Question 4

What is meant by a weak acid?

Answer 4

Partially dissociates

Question 5

Definition of PH

Answer 5

pH = -log10[H+]

Question 6

Definition of [H+]

Answer 6

[H+] = 10-pH

Question 7

Definition of the ionic product of water (Kw)

Answer 7

Kw = [H+][OH-]

Question 8

What equation should be used when calculating the pH of a strong acid?

Answer 8

pH = -log10[H+]

Question 9

What equation should be used when calculating the pH of a weak acid?

Answer 9

Ka = [H+]2 / [HA]
Rearrange to get [H+]

Question 10

What equation should be used when calculating the pH of a buffer?

Answer 10

Ka = [H+][A-] / [HA]
Rearrange to get [H+]

Question 11

metal + acid ……

Answer 11

salt + hydrogen

e.g. HCl (aq) + Na (s) —> NaCl (aq) + 1/2 H2 (g)

hydrochloric acid + sodium —> sodium chloride + hydrogen

Question 12

metal oxide + acid ……

Answer 12

salt + water

e.g. 2HNO3 (aq) + K2O (aq) —> 2KNO3 (aq) + H2O (l)

nitric acid + potassium oxide —> potassium nitrate + water

Question 13

acid + metal hydroxide …..

Answer 13

salt + water

e.g. H3PO4 (aq) + 3NaOH (aq) —> Na3PO4 (aq) + 3H2O (l)

phosphoric acid + sodium hydroxide —> sodium phosphate + water

Question 14

acid + metal carbonate …..

Answer 14

salt + water + carbon dioxide

e.g. H2SO4 (aq) + Na2CO3 (s) —> Na2SO4 (aq) + CO2 (g) + H2O (l)

sulfuric acud + sodium carbonate —> sodium sulfate + carbon dioxyde + water

Question 15

ammonia + acid ….

Answer 15

salt

e.g. NH3 (aq) + HCl (aq) —> NH4Cl (aq)

ammonia + hydrochloric acid —> ammonium chloride

e.g. NH3 (aq) + H3PO4 (aq) —> (NH4)3 PO4 (aq)

Question 16

What is a monoprotic acid?

Answer 16

only one H+ ion released e.g. HCl

Question 17

What is a diuretic acid?

Answer 17

two H+ ions released e.g. H2SO4

Question 18

What does smaller pH mean in terms of [H+]

Answer 18

Higher concentration of [H+]

Question 19

What are the 4 main examples of strong acids?

Answer 19

• HCl
• H2SO4
• HNO3
• H3PO4

Question 20

Where does the position of equilibrium for strong acids usually lie?

Answer 20

entirely to right side

Question 21

Where does the position of equilibrium for weak acids usually lie?

Answer 21

More to the left side

Question 22

How to find pKa from Ka?

Answer 22

pKa = -log10Ka

Question 23

How to find Ka from pKa?

Answer 23

Ka = 10-pKa

Question 24

What is the Kw value for water?

Answer 24

1 x 10-14 mol2dm-6

Question 25

Why is water always neutral?

Answer 25

[OH-] = [H+]

Question 26

How can [H+] be found from Kw?

Answer 26

Kw = [H+]2

Question 27

How can Kw] be found from [H+]?

Answer 27

[H+] = square root of Kw

Question 28

Strong bases...

Answer 28

- fully dissociate - to release OH- ions

Question 29

Where does the position of equilibrium for strong bases usually lie?

Answer 29

entirely on right side

Question 30

Equation to find [H+] of strong alkalis

Answer 30

[H+] = Kw / [OH-]

Question 31

Suggest why pure water is not alkaline

Answer 31

[H+] = [OH-]

Question 32

Explain why [H2O] is not shown in the Kw expression

Answer 32

[H2O] is (almost) constant

Question 33

A student has an unknown weak acid of unknown concentration and a bottle of 0.5 mol dm-3 NaOH. Explain, using brief practical details, how you would determine the Ka of the weak acid. [6]

Answer 33

- Measure 25 cm3 of acid into a beaker/conical flask using volumetric pipette. - Use a pH probe to measure the initial pH - Add 1cm3 NaOH from a burette swirl and record the pH - Repeat until the NaOH is in excess - Plot a graph of pH against vol NaOH added in cm3 - Use the vertical section to find the volume of NaOH needed for neutralisation - The half neutralisation point is half the volume of neutralisation. - Read off the pH at the half neutralisation point. - At half neutralisation ka = [H+]/pKa=pH - Ka = 10-pH

Question 34

write equation to show how ethanoic acid behaves as a weak acid in it's reaction with water

Answer 34

CH3COOH ---> CH3COO- + H+

Question 35

write equation when pure ethanoic acid reacts with pure nitric acid where ethnic acid acts as a base

Answer 35

CH3COOH + HNO3 ---. CH3COOH2+ + NO3 2-

Question 36

explain why chloroethanoic acid is stronger than ethanoic acid

Answer 36

- electronegative chlorine withdraws electrons - weakens O-H bond

Question 37

explain why data books do not usually contain Ka values for strong acids

Answer 37

- strong acids completely dissociate - ka for strong acids is very large

Question 38

state how buffer solution made

Answer 38

add excess weak acid to alkali

Question 39

state how buffer solution resists changes in PH

Answer 39

CH3COO- from salt reacts with H+