Buffers and indicators

Question 1

Define buffer

Answer 1

solution which resist changes of acidity and alkanity when small quantities of acid and alkali is added

Question 2

Whats the equation for buffers?

Answer 2

HA –> H+ + A-

Question 3

Describe adding small amount of acid

Answer 3

Add H+ increasing H+ conc
H+ react with A-
Eqm shifts to left to reduce H+ ions

Question 4

Describe adding small amount of alkali

Answer 4

Add OH- increasing OH- conc
React with H+ to produce H2O
Eqm shifts to right to replace H+ that have reacted

Question 5

How do you work out pH of buffers if its acids and their salts?

Answer 5

Conc of HA and A-
Ka expression to get H+
pH

Question 6

What are the indicators used?

Answer 6

SA and SB - Phenolphthalein
SA and WB - Methyl red
WA and SB - Phenolphthalein

Question 7

Describe colour change of indicators?

Answer 7

Increase in H+ shifts to left - Red

Increase in In- shifts to right - blue

Question 8

Define equivalence point

Answer 8

When sufficient acid has been added to neutralise

volume when moles are equal

Question 9

Define end point

Answer 9

volume of acid and alkali added when colour changes