Acids & Bases

Question 1

Definition of acid

Answer 1

Proton donor

Question 2

Definition of base

Answer 2

Proton acceptor

Question 3

Definition of strong acid

Answer 3

An acid which fully dissociates

Question 4

Definition of weak acid

Answer 4

An acid which partially dissociates

Question 5

Definition of pH

Answer 5

pH = -log10 [H+]

Question 6

Definition of [H+]

Answer 6

[H+] = 10-pH

Question 7

Ionic product of water (Kw)

Answer 7

Kw = [H+][OH-]

Question 8

Calculating pH of strong acid

Answer 8

pH = -log10 [H+]

Question 9

Calculating pH of a strong base

Answer 9

Rearrange Kw = [H+][OH-] to get [OH-]
then use pH = -log10 [H+]

Question 10

Calculating pH of a weak acid

Answer 10

Ka = [H+]2 ÷ [HA]
and rearrange to get [H+]

Question 11

Calculating pH of a buffer

Answer 11

Ka = [H+][A-] ÷ [HA]
and rearrange to get [H+]

Question 12

Acid + Metal →

Answer 12

Acid + Metal →Salt + Hydrogen

Question 13

Acid + Metal Oxide →

Answer 13

Acid + Metal Oxide →Salt + Water

Question 14

Acid + Metal Hydroxide →

Answer 14

Acid + Metal Hydroxide → Salt + Water

Question 15

Acid + Metal Carbonate →

Answer 15

Acid + Metal Carbonate →Salt + CO2 + Water

Question 16

Examples of strong acids:

Answer 16

HCl
H2SO4
HNO3
H3PO4

Question 17

Group 1 is called the ‘Alkali Metals’ and Group 2 is called the ‘Alkaline Earth Metals’. As such the oxides of Na and Mg are both alkaline and react with water to form basic solutions

Answer 17

Eg:

Na2O(s) + H2O(l) → 2Na+(aq) + 2-OH(aq

MgO(s) + H2O(l) → Mg(OH)2(aq)

Question 18

Period 3 Oxides:
Magnesium hydroxide

Answer 18

Magnesium hydroxide is sparingly soluble and so is weakly alkaline

Question 19

Acids:

Answer 19

Any substance which dissociates to release H+ ions is classed as an acid

Question 20

Base:

Answer 20

Any substance which will accept and bond to an H+ ion is classed as a base

Question 21

Definition of amphoteric

Answer 21

When water can act as an acid or a base

Question 22

Key points of pH scale:

Answer 22

1) The smaller the pH, the greater the concentration of H+ ions
2) A difference of 1 on pH scale means a 10x difference in [H+]
3) It is possible to have a pH below 0 for very strong acids and a pH above 14 for a very strong base

Question 23

pH for diprotic acids and triprotic acids
eg: H2SO4 & H3PO4

Answer 23

pH = -log10 [H+ × 2]

pH = -log10 [H+ × 3]

Question 24

Method for weak acid pH calculations:

Answer 24

1) write out dissociation of weak acid
2) construct a Ka expression for the acid
3) simplify Ka expression using [H+]2
4) rearrange expression to get [H+] on its own
5) substitute value of [H+] I to pH equation

Question 25

pKa

Answer 25

pKa = -log10Ka

Question 26

Ka

Answer 26

Ka = 10-pKa

Question 27

Kw is called the ionic product of water and at 298K has a value of 1x10-14mol2dm-6 The value of Kw will alter with temperature

Question 28

Why is pure water always neutral?

Answer 28

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