Acids and Bases

Question 1

What is an acid

Answer 1

An acid is a proton donor

Question 2

What is a base

Answer 2

A base is a proton acceptor

Question 3

What is an alkali

Answer 3

A base that is soluble

Question 4

What is a strong acid

Answer 4

An acid which fully dissociates into its ions

HA—–> H+ + A-

Question 5

Give 4 examples of strong acids and how they dissociate

Answer 5

HCl —-> H+ + Cl- monoprotic
H2SO4 ———> 2H+ + SO4^2- diprotic
HNO3 ———> H+ + NO3- monoprotic
H3PO4 ———> 3H+ + PO4^3- triprotic

Question 6

What is a weak acid

Answer 6

An acid which only slightly dissociates into its ions

HA <===> H+ + A-

Question 7

Give an example of a weak acid

Answer 7

-All organic acids e.g. ethanoic acid CH3COOH
-Any other acid that is not a strong acid

Question 8

State the 5 types of acid-base reactions

Answer 8

1) Acid + Metal ——–> Salt + Hydrogen
2) Acid + Metal Oxide ———-> Salt + Water
3) Acid + Metal Hydroxide ——–> Salt + Water
4) Acid + Metal Carbonate ——–> Salt + CO2 + Water
5) Acid + Ammonia ———> Ammonioum + whats left

Question 9

Define pH

Answer 9

pH=-Log10[H+]

Rearranges to [H+]=10^-pH

Question 10

How do you calculate the pH of a strong acid

EG monoprotic, diprotic

Answer 10

[HA]= conc of strong of strong acid

monotropic pH=-Log10[HA]
Diprotic (H2SO4) pH=-Log10[H+]—–> Ph=-log[2HA]

ect

Question 11

How do you calculate the pH of a weak acid

Answer 11

ka= products/reactants

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

1:1 Ratio so

Ka= [H+]^2/[HA]
Can rearrange to fine conc of acid [H+]

[H+]=√ka[HA]

Question 12

Pure water

Answer 12

Pure water only VERY slightly dissociates

H2O <====> H+ + OH-

Question 13

How do you calculate the pH of pure water

Answer 13

Kw=[H+][OH-]
No H2O at bottom as this is a constant
[H+]^2= Kw
[H+]=√Kw

Question 14

Why is pure water always neutral

Answer 14

Because [H+]=[OH-]
The conc of H+ equals to conc of OH-

Question 15

Strong Alkalis

Answer 15

A strong acid fully dissociates

MOH—–> M+ + OH-

Question 16

How do you calculate the pH of a strong alkali

Answer 16

Kw=[H+][OH-]

[H+]= Kw/[OH-]

[H+]= kw/[nMOH]

-n= number of OH- in formula of alkali (mono, di,tri)

Question 17

Give the equation of pKa and it’s rearranged form

Answer 17

Question 18

Define buffer solution

Answer 18

A buffer is a solution that can resist changes in pH when a small amount of acid or base is added

Question 19

Define acidic buffer and basic buffer

Answer 19

Acidic buffer- Made of a weak acid and a soluble salt of that acid, maintains a pH below 7

Basic buffer- Made of a weak BASE and a soluble salt of the BASE, maintains a pH above 7

Question 20

How do acidic buffers work when added to an
Acid
Base

Answer 20

Question 21

How do basic buffers work when added to an
-acid
-base

Answer 21

Question 22

Outline the steps in a normal titration

Answer 22

Question 23

Outline the steps for a pH titration

Answer 23

Question 24

Why do you need to calibrate a pH meter before use

Answer 24

• After storage pH meter may not produce accurate readings
• To calibrate place the pH meter in a solution of known pH and adjust the meter accordingly

Question 25

What are the 4 pH titration graphs, sketch them

Answer 25

Question 26

What are the key points of the pH titration graphs

Answer 26

Question 27

What is the half- neutralisation point

Answer 27

The volume halfway between 0 and the equivalence point

It is useful when carrying out buffer calculations because:

[weak acid]=[salt]

Question 28

Define equivalence point

Answer 28

When exactly enough acid has been added to neutralise the base (or vice versa)

Question 29

Define end point

Answer 29

The exact volume of acid or base which needs to be added to cause an indicator to change colour

Question 30

How do you know if an indicator is suitable

Answer 30

Question 31

What would be a suitable indicator for this graph

Answer 31

Question 32

Find Ka for the half equivalence point on this graph

Answer 32