Topic 21 Equilibria

Question 1

Bronsted Lowry: Acid and Bases are?

Answer 1

Acids are proton donors and bases are proton acceptors

Question 2

What is the definition of a conjugate pair?

Answer 2

An acid-base pair on each side of an acid-base equilibrium equation that are related to each other by the difference of a hydrogen ion e.g. the acid in the forward reaction and base in the backward reaction e.g.

NH3(aq) +H2O(l) <-> NH4^+(aq)+OH^-(aq)

Question 3

NH3(aq) +H2O(l) <-> NH4^+(aq)+OH^-(aq)

What the conjugate pairs?

Answer 3

Ammonia (base) and the ammonium ion (acid)

Water (acid) and hydroxide ion (base)

Question 4

Square brackets indicate?

Answer 4

Square brackets represent the concentration of a substance

Question 5

Kw

Answer 5

Kw= [H^+][OH^-]
at 298k gives 1.00*10^-14
Def: The equilibrium constant for the ionisation of water

Question 6

What does the equilibrium reaction for water look like?

Answer 6

H2O + H2O <-> H3O^+ +OH ^-

Question 7

What is another way of writing this where we use [H^+] instead of [H3O^+]?

Answer 7

H2O <-> H^+ + OH^-

Question 8

For water [H^+]=[OH^-]
What does this tell you about the acidity/alkalinity of water?

Answer 8

Water is always neutral at 298k

Question 9

pH=

Answer 9

-log10[H+]

Question 10

Calculating [H+] from pH

Answer 10

[H^+] = 10^-pH

Question 11

What is the pH (and is it neutral/acid/alkaline) of:
[H+]= 10^-7 10^-14 10^-3 10^-9 310^-7 4.510^-4 6.12*10^-11

Answer 11

pH= 7 14 3 9 6~7 3~4 10~11

Question 12

Name a strong monoprotic, diaprotic and triprotic acid

Answer 12

Hydrochloric acid, Sulphiric acid and Phosphoric acid

Question 13

pH of strong acids

Answer 13

Strong acids completely dissociate in solution; it follow that the concentration of hydrogen ions in solution is approximately the same as the concentration of acids

Question 14

Calculating pH of strong acid
e.g. pH of 0.1moldm^-3 HCl

Answer 14

-log10(1*10^-1)= pH1

Question 15

Give the equilibrium dissociation reactions for hydrochloric and sulphiric acid

Answer 15

HCL <-> H^+ + Cl^-

H2SO4 <-> H^+ + HSO4^- and HSO4- <-> SO4^2-

Question 16

Diluting the acid 10x

Answer 16

reduces the value of the H^+ ion concentration to one-tenth and increases the pH by a value of one

Question 17

Buffer solution

Answer 17

a solution in which the pH does not change significantly when small amounts is acids or alkalis are added. A buffer solution is to keep the pH (almost) constant.