Acids and Bases

Question 1

What is the definition of a Bronsted-Lowry acid?

Answer 1

A proton donor

Question 2

What is the definition of a Bronsted-Lowry base?

Answer 2

A proton acceptor

Question 3

How do you calculate the pH? (Using [H+])

Answer 3

pH = -log [H+]

Question 4

How can you use the concentration of H+ ions to work out pH?

Answer 4

pH = -log(H+)

Question 5

HX –> H+ + X-
State whether this is a strong or weak acid, and give a reason why

Answer 5

Strong
DIssociates completely

Question 6

How do you calibrate a pH meter?

Answer 6

Rinse probe thoroughly with deionised water, and shake gently to remove excess
Place probe in standard soln. of 4.00pH and record
Repeat process using standard ph 7.00 and 9.20 buffer soln.
Plot a graph of recorded pH (x) vs pH of buffer soln. (y)
Can be used to convert experimental readings into more accurate ones

Question 7

What is Kw?

Answer 7

The ionic product of water
Kw = [H+][OH-] (x^2)
= 1.00 x 10-14 mol^2dm^-6

Question 8

How do you work out the acid dissociation constant?

Answer 8

Ka = [H+][X-] / [HX]

Question 9

How do you work out pKa?

Answer 9

pKa = -logKa

Question 10

Describe step-by-step how you would work out the pH if it was strong acid vs strong base, and the acid was in excess

Answer 10

1) find moles of acid
2) find moles of base
3) which is in excess?

ACID IN XS
calculate conc. of [H+]
calculate pH using [H+]

Question 11

Describe step-by-step how you would work out the pH if it was strong acid vs strong base, and the base was in excess

Answer 11

1) find moles of acid
2) find moles of base
3) which is in excess?

BASE IN XS
calculate [OH-]
use Kw to calculate [H+]
calculate pH using [H+]

Question 12

Describe step-by-step how you would work out the pH if it was weak acid vs strong base, and the acid was in excess

Answer 12

1) find moles of acid
mole of base
XS –> ACID
calculate moles of HA left and A- formed
[HA]+[A-] (not always nec.)
calculate [H+] conc using Ka
calculate pH from [H+]

Question 13

Describe step-by-step how you would work out the pH if it was weak acid vs strong base, and the base was in excess

Answer 13

mol of acid
mol of base
XS? –> BASE
calculate [OH-]
use Kw to calculate [H+]
calculate pH using [H+]

Question 14

What does acidic buffer contain?

Answer 14

A weak acid and the salt of that weak acid

Question 15

What does basic buffer contain?

Answer 15

A weak base and the salt of that weak base

Question 16

What is a buffer?

Answer 16

A solution that maintains an approximately constant pH, despite dilution or addition of small amounts of acid or
base.

Question 17

How does adding acid affect an acidic buffer?

Answer 17

A- + H+ –> HA
Salt ions ‘mop up’ added H+

Question 18

How does adding a base affect an acidic buffer?

Answer 18

HA + OH- –> A- H2O
The acid (HA) can ‘mop up’ the added OH-

Question 19

How does adding a base affect a basic buffer?

Answer 19

NH4+ + OH- –> NH3 + H2O
Salt can ‘mop up’ added OH-

Question 20

How does adding an acid affect a basic buffer?

Answer 20

NH3 + H+ –> NH4+
Eqm shifts to right
Weak base ‘mops up’ added H+

Question 21

What is the definition of an Arrhenius acid?

Answer 21

Any substance that adds H+ to water

Question 22

What is the definition of an Arrhenius base?

Answer 22

Any substance that adds OH- to water

Question 23

Where is the neutralisation points of titration curves for different combinations of acids and bases?

Answer 23