Buffers

Question 1

What is a buffer?

Answer 1

Solution that has the ability to resist pH changes upon addition of small amount if acid or base

Question 2

How do you form buffer?

Answer 2

WA + salt

WB + salt

Question 3

What is pH =?

Answer 3

pKa

Question 4

What is the equation for pKa?

Answer 4

pH + log ([HA]/[A-])

Question 5

What happens when acid acid is added?

Answer 5

Conjugate base neutralise added acid

Eqm shift right

Question 6

What happens when base is added?

Answer 6

Conjugate base neutralise added base

Eqm shift right

Question 7

When do buffers function best?

Answer 7

When pKa of conjugate WA is close to desired working range of buffer
When conc of conjugate acid + base approx. equal

Question 8

What does the pKa of conjugate acid determine?

Answer 8

Approx. pH of buffer

Question 9

How do buffers work?

eg. Hydrofluoric acid + Sodium fluoride

Answer 9

HF = WA
HF (aq) + H2O (l) ⇌ F- (aq) + H3O+ (aq)
Can add NaF to reach desire vol + pH of buffer
NaF (aq) + H2O (l) —-> Na+ (aq) + F- (aq)

Question 10

Why does Na+ have no effect on pH of buffer?

Answer 10

Conjugate of SB

Question 11

Why does NaF increase conc of F-?

Answer 11

Slightly less dissociation of HF in previous eqm