3.1.12 acids and bases

Question 1

define acid

Answer 1

proton donor

Question 2

define base

Answer 2

proton acceptor

Question 3

define strong acid

Answer 3

fully ionises/dissociates in solution

Question 4

define weak acid

Answer 4

partially ionises/dissociates in solution

Question 5

what is the equation for PH?

Answer 5

ph = - log[H+]

Question 6

how do you find the [H+] if you know the ph?

Answer 6

[H+] = 10^-ph

Question 7

what is the equation for the acid dissociation constant in weak acids?

Answer 7

ka = [H+][A-] / [HA]

Question 8

what is [H+][A-] the same as?

Answer 8

[H+]^2

Question 9

which statement about PH is correct?
a) the PH of a weak base is independent of the temperature
b) at temperatures above 298K, the PH of pure water is less than 7
c) the PH of 2.0 moldm-3 nitric acid is approximately 0.30
d) the PH of 0.10 moldm-3 sulfuric acid is greater than that of 0.10 moldm-3 hydrochloric acid

Answer 9

b

Question 10

a 0.10 moldm-3 aqueous solution of an acid is added slowly to 25cm3 of 0.10 moldm-3 aqueous solution of a base
Which acid-base pair has the highest pH at the equivalence point?
a) CH3COOH and NaOH
b) CH3COOH and NH3
c) HCl and NaOH
d) HCl and NH3

Answer 10

a

Question 11

explain why [H2O] is not shown in the kw expression (1 mark)

Answer 11

[H2O] is almost constant

Question 12

explain why the value of kw increases as the temperature increases (2 marks)

Answer 12

M1: equilibrium is endothermic
M2: equilibrium shifts to the right hand side to oppose temperature change

Question 13

suggest why the pH probe is washed with distilled water between each of the calibration measurements (1 mark)

Answer 13

different solutions must not contaminate each other

Question 14

explain why the volume of sodium hydroxide solution is added between each pH measurement is smaller as the end point of the titration is approached (1 mark)

Answer 14

to avoid missing the end point

Question 15

state why all three of the indicators in table 2 are suitable for this titration (1 mark)

Answer 15

all have a colour change within the steep part of the titration curve

Question 16

Some sodium sulfate is dissolved in a sample of the solution from part (d)
Explain why this increases the pH of the solution (2 marks)

Answer 16

M1: equilibrium shifts left to counteract increased concentration of sulfate
M2: so [H+] decreases