Buffers And Neutralisation

Question 1

Define a buffer

Answer 1

A solution that resists changes to pH when small amounts of alkali or acid are added

Question 2

What are the components of a buffer

Answer 2

Weak acid and its conjugate base

Question 3

Will the pH of a buffer change

Answer 3

Yes, only slightly

Question 4

Why might a buffer stop working

Answer 4

When one component is used up

Question 5

What can be mixed together to form a buffer

Answer 5

Weak acid and the salt of its conjugate base

Weak acid and alkali

Weak acid and some conjugate base

Question 6

What assumptions are made with buffers

Answer 6

All conjugate base ion comes from the salt

Almost all acid remains undissociated

Question 7

What will occur is acid is added to a buffer

Answer 7

Conc H+ increases which reacts with A-

So Position of equilibrium moved to the left

Question 8

What occurs when an alkali is added to a buffer

Answer 8

Conc OH- increases reacts with H+

Conc H+ decreases so position of equilibrium moves to right increasing H+ conc

Question 9

When are buffers most effective

Answer 9

When conc HA = conc A-

pH=pKa of HA

Question 10

What is the pH of the blood

Answer 10

7.4

Question 11

What occurs if the blood is too acidic

Answer 11

Acidosis

Question 12

What occurs if the blood is too alkali

Answer 12

Alkalosis

Question 13

How do you create a titration curve using a pH meter

Answer 13

Use pipette to measure 25cm3 of acid

Place electrode in and calibrate to 0

Add alkali to burette and add to acid 10cm3 at a time.

Record pH each interval

Once pH starts to increase rapidly and a drop and measure pH

Once increase begins to slow add 10cm3 at a time again

Stop once pH stays constant

Question 14

What is the equivalence point

Answer 14

The exact volume of one solution needed to completely react with the other

Question 15

What is the end point

Answer 15

When the indicator changes colour

HA conc = A- conc of indicator

Question 16

What are indicators made of

Answer 16

Weak acids

Question 17

How do you choose an indicator to use

Answer 17

One that has a distinct color change and coincides with vertical section of titration curve

End point = equivalence point

Question 18

Describe the titration graph of a strong acid strong base reaction

Answer 18

Very low pH at start
Very high pH at end
pH at equivalence is 7

Question 19

Describe the titration graph of a strong acid weak base reaction

Answer 19

Very low pH at start
high pH at end
pH at equivalence is < 7

Question 20

Describe the titration graph of a weak acid strong base reaction

Answer 20

low pH at start
Very high pH at end
pH at equivalence > 7

Question 21

Describe the titration graph of a weak acid weak base reaction

Answer 21

low pH at start
high pH at end
pH at equivalence depends on dissociation

Question 22

What will occur to a titration curve if the conc of base is increased (base add to set vol of acid)

Answer 22

Shifted to left

Question 23

What will occur to a titration curve if the conc of base is increased (base add to set vol of acid)

Answer 23

Hh