Chapter 20: Acids, Bases and pH

Question 1

Acids

Answer 1

• Proton donors
• dissociate + release H+ in aqueous solution

Question 2

Alkalis

Answer 2

• proton acceptor
• dissociate + release OH- in aqueous solution

Question 3

Neutralisation

Answer 3

H+(aq) + OH-(aq) -> H2O(aq)

Question 4

Hydronium ion (H3O+)

Answer 4

active acid ingredient in any aqueous acid

Question 5

Different types of acids

Answer 5

• Monobasic
• Dibasic
• Tribasic
• Refers to the total number of H+ ions in the acid that can be replaced per molecule in an acid-base reaction

Question 6

Types of salts equations

Answer 6

MASH
AAWS
BAWS
CAWCS

Question 7

pH

Answer 7

A logarithmic scale

Question 8

Relationship between [H+] and pH

Answer 8

inversely proportional (as one increases, the other decreases)
pH = -log[H+]
[H+] = 10^-pH

Question 9

What does a change in pH by 1 cause?

Answer 9

10 times difference in [H+]
10^x

Question 10

Calculating the pH of strong acids

Answer 10

• Strong acids fully dissociate
  HA -> H+ + A-
  Therefore [H+] = [HA} for strong acids

Question 11

How many significant figures do you give pH to?

Answer 11

2

Question 12

Calculating the pH of weak acids

Answer 12

• Weak acids partially dissociate
  Ka = [H+][A-]/[HA] = [H+]2/[HA]

Question 13

Relationship between Ka value and strength of an acid

Answer 13

The larger the Ka value, the more dissociation, so the stronger the acid

Question 14

Ka and pKa equations

Answer 14

pKa = -logKa
Ka = 10^-pKa

Question 15

Relationship between Ka and pKa

Answer 15

Inversely proportional

Question 16

Why is pKa used?

Answer 16

Easier to compare acid strengths

Question 17

Approximation 1

Answer 17

[H+]eqm. = [A-]eqm.
There is a small dissociation of H+ from H2O but this is ignored

Question 18

Approximation 2

Answer 18

[HA]start = [H+]eqm.
as you can neglect any decrease in the conc.. of HA from dissociation because dissociation of weak acids is small

Question 19

Determination of Ka experimentally

Answer 19

• Prepare a standard solution of the weak acid of known concentration
• measure the pH using a pH meter

Question 20

Ionisation of water

Answer 20

• Water ionises very slightly (very small dissociation)

Question 21

Kw

Answer 21

[H+][OH-]

Question 22

Kw at 298K (standard conditions)

Answer 22

1.00 x 10^-14
sets up the neutral point on the pH scale

Question 23

Conc. of acidic solution

Answer 23

[H+]>[OH-]

Question 24

Conc. of neutral solution

Answer 24

[H+]=[OH-]

Question 25

Conc. of alkaline solution

Answer 25

[H+]<[OH-]

Question 26

Alkali

Answer 26

Soluble base that releases OH- ions in aqueous solution

Question 27

Strong base

Answer 27

alkali that completely dissociates in solution

Question 28

What is needed to calculate the pH of a strong base

Answer 28

• Kw
• Conc. of base

Question 29

What type of reaction is the ionisation of water?

Answer 29

Endothermic