Acids bases and Buffers

Question 1

What is a Bronsted- lowry acid ?

Answer 1

• proton donor

Question 2

What is a bronsted-lowry base ?

Answer 2

• proton acceptor

Question 3

equation to work out pH

Answer 3

-log(h+)

Question 4

what is a strong acid + weak acid

Answer 4

• strong acid = fully dissociates in aqueous solutions to release H+ ions
• weak acid = partially dissociates in aqueous solutions

Question 5

How do u work out ph of a weak acid

Answer 5

• using ka
• assume (h+) conc = (a-)
  so ka = (H+) 2/( Ha)

Question 6

What is the effect of temperature on Kw

Answer 6

-increasing temp, favours endothermic reaction
- dissociation of water is endo
- so equilibrium shifts to the right and kw increases

Question 7

units for kw

Answer 7

mol2 dm-6

Question 8

how do u calculate ph for a strong base

Answer 8

kw = (H+)(OH-)
(h+) = Kw/ (oh-)
-log(H+)

Question 9

what is a buffer

Answer 9

a solution that minimises changes in pH upon addition of a small amount of acid or base

Question 10

what are the 2 ways to make a buffer solution

Answer 10

• a weak acid and its conjugate base
• excess of weak acid + strong acid

Question 11

what is pka

Answer 11

• log(ka)

Question 12

how does pka + ka affect strength of an acid

Answer 12

• stronger acid has larger ka + smaller pka

Question 13

how is the ph of a buffer solution calculated

Answer 13

(H+) = ka x acid / salt
- log (H+)

Question 14

what is the equivalence point ?

Answer 14

• mol of h+ = oh-
  vertical section of curve

Question 15

what is phenolphthalein indicator used for

Answer 15

• changes colour at high ph so weak acid/strong base

Question 16

what is methyl orange indicator used for

Answer 16

• changes colour at low ph so strong acid/ weak base

Question 17

for which acid base =titration is no indicator suitable -

Answer 17

weak acid/ weak base because no sharp pH change

Question 18

how to calculate ph of a buffer made from partial nuetralisation (eg. HCOOH + NaOH)

Answer 18

• find mol of NaOH added
• mol (HCOO-) formed = use ratio from NaOH
• mol of (HCOOH) used
• remaining mol of (HCOOH)
• find conc using new volume
  calculate (h+) = kacid / salt