20 - Acids / Bases And PH

Question 1

Bronsted Lowry acid definition

Answer 1

Proton donor

Question 2

Bronsted Lowry base

Answer 2

Proton acceptor

Question 3

Dibasic acid

Answer 3

Releases 2 protons per molecule

Question 4

Conjugate acid base pair

Answer 4

Contains 2 species inter converted by transfer of a proton

Question 5

How to calculate pH of strong acid

Answer 5

Use
pH= -log(H+)
Fully dissociates

Question 6

How to find (H+)

Answer 6

Use 10^-pH

Question 7

What is a strong acid

Answer 7

Completely dissociates in aqueous solutions

Question 8

Strong acid examples

Answer 8

HCl
H2SO4
HNo3
HBr

Question 9

Weak acid examples

Answer 9

CH3COOH
HNO2
H3PO4

Question 10

Strong base examples

Answer 10

NaOH
KOH
Ca(OH)2

Question 11

Weak bases examples

Answer 11

NH3

Question 12

Why is pKa used

Answer 12

Too difficult to compare numbers with negative indices

Question 13

Relationship between ka and pKa for stronger acids

Answer 13

Stronger acids
Larger Ka
Smaller pKa

Question 14

Relationship between ka and pKa for weaker acids

Answer 14

Weaker acids
Lower Ka
Larger pKa

Question 15

Equilibrium of weak acids

Answer 15

HA H+ + A-

Question 16

Approximations used for weak acids

Answer 16

Only a bit of HA dissociates
- (HA)> (H)+ So … (HA)start = (HA)equilibrium

Assume dissociation of acid is much greater that dissociation of water - assume all H+ ions come from acid
- (H+) = (A-)

Question 17

Why can’t the approximations of weak acids be used for strong

Answer 17

Strong acids dissociate more
The difference between
(HA)start = (HA)equilibrium Becomes more significant

Assumptions no longer valid

Question 18

Determination of Ka for a weak acid experimentally

Answer 18

Preparing standard solution of weak acid

Measuring pH using pH meter

Question 19

When are the approximations not true

Answer 19

Don’t work for very weak acids ph>6
- dissociation or water will be significant compared to dissociation of acid

Not justified for stronger weak acids with Ka > 10^-2
- doesn’t work when (H+) becomes significant

Question 20

What is kw

Answer 20

The ionic product of water

Ions H+ and OH- multiplied together

Question 21

What is the value of KW

Answer 21

1 x 10^-14 mol2dm-6