12: Acids, Bases and pH

Question 1

What is a Bronsted Lowry acid and base?

Answer 1

Acid - Proton donor
Base - Proton acceptor

Question 2

What is the definition for an acid?

Answer 2

A substance that reacts with water to form H+ ions.

Question 3

What is the difference between monoprotic and diprotic acids? Give an example of each.

Answer 3

Monoprotic acids donate 1H+ when they dissociate eg: HCl
Diprotic acids donate 2H+ when they dissociate eg: H2SO4

Question 4

Describe how strong acids dissociate in water.

Answer 4

They dissociate fully into water, meaning nearly all of the H+ ions will be released.

Question 5

Describe how weak acids dissociate in water.
What is formed during the dissociation of weak acids.

Answer 5

They only dissociate partially, meaning only a few H+ ions are released. This forms an equilibrium, meaning weak acids are usually part of reversible reactions.

Question 6

Describe proton donation in acid/base reactions.

Answer 6

Protons from the acid (H+) are donated to the base which accepts them.

Question 7

What happens when acids and water react?

Answer 7

Water acts as an base to accept the proton.

Question 8

Give the formula for calculating pH using H+ ion concentration.

Answer 8

pH = -log(H+)

Question 9

Give the formula for calculating H+ concentration from pH.

Answer 9

H+ = 10^-pH

Question 10

Give the equation for the dissociation of water.

Answer 10

H2O (l) + H2O (l) (reversible) H3O+ + -OH

Question 11

Give an equation for Kc for the dissociation of water from the previous equation.

Answer 11

Kc = [H+] [-OH]
—————-
[H2O]

Question 12

What constant is formed if you multiply Kc by H2O?
Give an equation for multiplying Kc and the new constant that forms.

Answer 12

Kc [H2O] = [H+] [-OH]
Kw = [H+] [-OH]

Question 13

What is Kw?

Answer 13

The ionic product of water. 1x10^-14

Question 14

Kw can be used to find the pH of which 2 substances?

Answer 14

Pure water.
Strong bases.

Question 15

What is pure water?
Describe its pH.

Answer 15

A substance that has an equal concentration of H+ ions and -OH ions
Its pH can be 7, but not always.

Question 16

Root of Kw tells us what? (pure water)
What is the opposite.

Answer 16

H+ concentration.
(H+^2) tells us Kw.

Question 17

Give the equation linking Kw, H+ and -OH.

Answer 17

Kw = [H+][-OH]

Question 18

Why is H2O not included in the Kw equation?

Answer 18

H2O is almost constant.

Question 19

Why does the value of Kw increase as temperature increases?
Give the equation that helps to explain this.

Answer 19

H2O (reversible) H+ + OH-
Equilibrium shifts to the right in the endothermic direction to minimise temperature change.

Question 20

What is Ka used to calculate?

Answer 20

pH of weak acids.

Question 21

What is Ka?

Answer 21

The acid dissociation constant.

Question 22

Give an equation linking Ka, H+, A- and HA, where Ka is the subject.

Answer 22

Ka = [H+] [A-]
————
[HA]

Question 23

Give an equation linking [HA] to [H+]^2 and Ka, where HA is the subject.

Answer 23

[HA] = [H+]^2
———-
Ka

Question 24

Give an equation linking for Ka where H+ is the subject.

Answer 24

H+ = ROOT [HA] [Ka]

Question 25

Give the equation for Ka where A- is the subject.

Answer 25

A- = [Ka] [HA] / [H+]

Question 26

Give the equation to calculate pKa

Answer 26

pKa = -log (Ka)

Question 27

Give the equation to calculate Ka.

Answer 27

Ka = 10^-pKa

Question 28

The bigger the Ka value….

Answer 28

The stronger the acid

Question 29

The smaller the pKa value……..

Answer 29

The stronger the acid.