1.12 Acids and Bases

Question 1

What is a bronsted lowry acid and base

Answer 1

A bronsted-lowry acid is a proton donor eg NH4+
A bronsted-lowry base is a proton acceptor eg OH-

Question 2

Define strong acid

Answer 2

An acid that completely dissociates to ions when in solution

Question 3

Define weak acid

Answer 3

An acid that only slightly dissociates when in solution

Question 4

Equation for pH

Answer 4

pH= -log10[H+]

Question 5

Equation for conc of H+

Answer 5

[H+]=10^-pH

Question 6

Equation for Kw and the constant value of it at 25C

Answer 6

Kw = [H+][OH-]
1x10^-14

Question 7

What is Kw

Answer 7

The equilibrium constant when water slightly dissociates to ions

Question 8

Equations involving Ka

Answer 8

Ka = 10^-pKa
pKa= -log10Ka
Ka=[H+][A-] / [HA]

Question 9

What to use when HA is in excess

Answer 9

[HA] [A-] and Ka to find H+ then pH

Question 10

What to use when A- is in excess

Answer 10

Use Kw to find[H+] then pH

Question 11

What to use when HA=A-

Answer 11

Find pKa as pKa=pH

Question 12

When does neutralisation occur for
1. Strong acid strong base
2. Strong acid weak base
3. Weak acid strong base
4. Weak acid weak base

Answer 12

1. pH 7
2. < pH7 (more acidic)
3. > pH7 (more basic)
4. normally pH 7 but hard to determine

Question 13

When is methylorange used and what colour does it turn when

Answer 13

More acidic neutralisation point
Red in acids and turns yellow at neutralisation point

Question 14

When is phenolphthalein used and what colour does it turn when

Answer 14

More basic neutralisation point
Pink in alkalis and colourless at neutralisation point

Question 15

What is a buffer solution

Answer 15

A solution which is able to resist changes in pH when small volumes of acid or base are added

Question 16

What do buffer solutions contain

Answer 16

Either a weak acid or a weak base and the salt of the weak acid/base

Question 17

How to work out pH for acid and base

Answer 17

Find moles of each species
Calc conc when at equilibrium using total volume
Use Ka to find [H+] and pH

Question 18

How to work out pH for acid and salt

Answer 18

Find moles of salt
Use Ka to find pH

Question 19

Why are buffers used

Answer 19

To keep systems regulated
Important as enzymes or reactions in living organisms often require a specific pH which can be maintained using a buffer solution

Question 20

Equation for ionisation of water

Answer 20

H2O(l) <–> H+(aq) + OH-(aq)

Question 21

Give examples of strong acids

Answer 21

HCl
H2SO4
H3PO4

Question 22

Examples of strong bases

Answer 22

NaOH
CaCO3
Na2CO3

Question 23

Examples of weak acids

Answer 23

CH3COOH

Question 24

Examples of weak bases

Answer 24

NH3

Question 25

Properties of a good indicator

Answer 25

Sharp colour change
Distinct colour change so its obvious when endpoint reached