Acids and Bases

Question 1

What is activity?

Answer 1

a modified concentration which accounts for energy loss when an ion divests itself of the oppositely charged ions around it (loss of reactivity)

Question 2

Activity equation?

Answer 2

(activity coefficient x concentration)/ standard molality

Question 3

Why do you divide by molality?

Answer 3

to make activity unitless

Question 4

what is activity in standard state?

Answer 4

1

Question 5

What happens at infinite dilution?

Answer 5

coefficient tends to 1 and activity = concentration

Question 6

What happens when an acid/base dissociates?

Answer 6

form conjugate base/conjugate acid

Question 7

What does a stronger base cause?

Answer 7

weaker conjugate acid

Question 8

why can you ignore effects of 2nd dissociation?

Answer 8

They will be that small that they wont really effect anything (cant ignore with H2SO4)

Question 9

equation for Kw and pkw (Learn how to derive them)

Answer 9

Kw = Ka x Kb
pKw = pKa + pKb = 14
Kw = [H30+][OH-], take logs pKw = pH + pOH

Question 10

What is a buffer solution?

Answer 10

a solution that can resist a change in pH when small amounts of strong acid/base are added, contains weak acid a d salt of a weak acid (conjugate base)

Question 11

What does the acid and conjugate base in the buffer do?

Answer 11

acid mops up -OH ions and conjugate base mops ip protons (as theyre both in large excess)

Question 12

How do you derive the equation for pH of a buffer?

Answer 12

write the Ka using the chemical equation and take -logs of it
pH = pKa + log([A-]/[HA])

Question 13

What does the pH of a buffer depend on?

Answer 13

The ratio of base to acid and the Ka

Question 14

What is buffer capacity?

Answer 14

amount of acid/base a buffer can neutralis without a significant change in pH

Question 15

When is buffer capacity max?

Answer 15

When [A-] = [HA]

Question 16

What is the buffer range?

Answer 16

The pH over which a buffer operates effectively

Question 17

What should you consider when choosing a buffer?

Answer 17

• choose a weak acid with a pKa close to the required pH
• choose the appropriate salt for the acid/base
• use the H-H equation to determine the ratio of [A-]/[HA]

Question 18

equivalence point for strong base/strong acid?

Answer 18

7

Question 19

equivalence point for weak acid/strong base?

Answer 19

8/9

Question 20

equivalence point for weak base/strong acid?

Answer 20

5/6

Question 21

What does the pH equal at the half equivalence point?

Answer 21

pH = pKa