1.12 Acids and Bases Part 1

Question 1

What do acid-base reactions involve

Answer 1

Proton transfer

Question 2

What is an acid

Answer 2

A subsantance that donates H+ ions

Question 3

What is a strong acid

Answer 3

Completley dissociates in solution

Question 4

What is a weak acid

Answer 4

Partially dissociates in solution

Question 5

What is a base

Answer 5

A subsatance that accepts H+ ions

Question 6

What is an alkali

Answer 6

A base that releases hydroxide ions in aqueous solution

Question 7

What is the role of H+ ions in the reaction of acids and bases

Answer 7

Acid = H+ donor
Base = H+ acceptor

Question 8

What is the role of H+ in the reaction of acids with alkalis

Answer 8

Acid = H+ donor
Base = H+ acceptor

Question 9

What is the role of H+ ions in the reaction of acids with metals

Answer 9

H+ ions = oxidising agent
REDOX reaction

Question 10

What is acid-base equilibria

Answer 10

Reversible reactions involving the transfer of protons

Question 11

How does water act in an acid-base reaction

Answer 11

Can act as either an acid or a base

Question 12

What is pH

Answer 12

The acidity of a solution depends on the conc of H+ ions

Question 13

What is the pH equation

Answer 13

pH = -log10[H+]

Question 14

What does a low and high pH mean

Answer 14

Low pH means a large conc of H+ ions
High pH means small conc of H+

Question 15

How do you convert between pH and [H+]

Answer 15

pH = -log10[H+]
[H+] = 10 ^ -pH

Question 16

How do you calculate the pH of a strong monoprotic acid

Answer 16

One mol of monoprotic acid donates one mol of H+ ions
Use ratio from balanced equation
Assume complete ionisation

Question 17

How does pH change relate to [H+]

Answer 17

When the pH of a solution changes by 1, the [H+] changes by a factor of 10

Question 18

How do you calculate the conc of a strong monoprotic acid from its pH

Answer 18

[H+] = 10 ^ -pH
For monoprotic acid, [HA]initial = [H+]

Question 19

What is the acid dissociation constant Ka for a weak acid

Answer 19

Ka = [H+] [A-] / [HA]
(Moldm-3)

Question 20

What does the Ka of a weak acid mean

Answer 20

Different weak acids have different Ka values. The value of Ka is a quantitative measure of the strength of a weak acid
The greater the dissociation, the greater the conc of products so Ka will increase

Question 21

What is pKa

Answer 21

Sometimes used to compare the relative strengths of acids

pKa = -log10Ka
The higher the Ka value the stronger the acid
The lower the pKa, the stronger the acid

Question 22

How do you calculate the pH of a weak acid from its initial conc and Ka

Answer 22

Assume-
[HA] equilibrium = [HA] inital
[H+] = [A-]

Calc Ka: [H+]^2 / [HA]
Calc [H+] and pH

Question 23

How do you calculate the conc of a weak acid from its pH and Ka

Answer 23

Calc Ka = [H+]^2 / [HA]
Calc [HA]

Question 24

How do you convert pKa to Ka

Answer 24

Ka = 10 ^ -pKa

Question 25

What is Kw

Answer 25

The ionic product of water Derived from the equilibrium constant for the dissociation of water into H+ ions and OH- ions

Question 26

What is the Kw equation

Answer 26

Kw = [H+] [OH-] at 298K, Kw = 1x 10-14

Question 27

What is the Kw equation for pure water

Answer 27

In pure water [H+] = [OH-] so Kw = [H+]^ 2

Question 28

What is the effect of temperature on Kw

Answer 28

The dissociation of water is endothermic becasue it involves bond breaking, which requires energy When temp is increased -Equilibrium shifts to the RHS in the endothermic direaction to oppose the increase in temp -So Kw increases -[H+] increases so the pH will decrease -Water is always neutral because [H+] = [OH-]

Question 29

How does Kw determine the concs ofthe ions in aquesous solutions

Answer 29

In any aqueous solution [H+] [OH-] = 1x10^ -14 mol2dm-6 at 298K - In acidic solutions, [H+] > [OH-] - In water and neutral solutions, [H+] = [OH-] - In alkaline solutions, [H+] < [OH-]

Question 30

How do you calculate pH of a strong base

Answer 30

Assume- Complete ionisation Kw = 1x10^ -14 mol2dm-6 at 298K Calc [OH-] Calc Kw = [H+][OH-] Calc [H+] Calc pH

Question 31

How do you calculate the conc of a strong base from its pH

Answer 31

Calc [H+] =10^ -pH Calc Kw = [H+][OH-] Calc [OH-]

Question 32

What is a weak base

Answer 32

A base which only partially dissociated in aqueous solution B + H+ <--> BH+