C2 Acid-base chemistry 2

Question 1

what is pH in general?

Answer 1

the negative log of hydronium ion concentration

Question 2

what does a pH difference of 1 mean?

Answer 2

a 10 fold difference in [H+]

Question 3

what is the formula for pH?

Answer 3

-log[H3O+]

Question 4

rearrange the pH equation so that [H3O+] is the subject

Answer 4

[H3O+] = 10^-pH

Question 5

what strong acid and strong base equations, what is assumed?

Answer 5

their reactions go to completion

Question 6

formula for Kw

Answer 6

Question 7

pH of solution of NaCl in water

Answer 7

7

Question 8

in an acid-base neutralisation reaction, if [H3O+] = [OH-], what happens?

Answer 8

• number of moles of strong acid = number of moles of strong base
• both reactants are fully consumed and water is produced
• pH of products is 7 (neutralisation)

Question 9

what are the steps for pH calculation in the case of incomplete neutralisation?

Answer 9

1. work out the excess amount (in moles) of H3O+ (or OH-) remaining after the addition
2. calculate the [H3O+] (or [OH-]) remaining after addition (in M). Take care to consider the total volume of the new solution
3. calculate pH

Question 10

describe and explain the accuracy of pH measurements

Answer 10

• rarely greater than 1 decimal place
• this is because of interactions between ions affecting the results

Question 11

equation linking pH, pKb, [B] and pKw when calculating the pH of a solution of a weak base

Answer 11

pH = pKw - 1/2pKb + 1/2log[B]

Question 12

equation linking pH, [HA] and pKa when calculating the pH of a solution of a weak acid

Answer 12

pH = 1/2pKa - 1/2log[HA]

Question 13

how can we convert the equation below into an equation in Ka?

pH = pKw - 1/2pKb + 1/2log[B]

Answer 13

use pKa + pKb = pKw

Question 14

variations of the Henderson-Hasselbalch equation

Answer 14