Acids and Bases

Question 1

what is a Bronsted-Lowry acid?

Answer 1

• a proton donor

Question 2

what is a Bronsted-Lowry alkali?

Answer 2

• a proton acceptor

Question 3

what is a weak acid/base?

Answer 3

• an acid/base that only slightly dissociates into ions in aqueous solutions

Question 3

Describe and Explain how temperature affects Kw

Answer 3

Kw increases with temperature
- equilibrium shifts to the endothermic direction to oppose the increase in temperature
- this leads to higher hydroxide and hydrogen ion concentrations which equal a higher Kw value

Question 3

what is a strong acid/base?

Answer 3

• an acid/base that completely dissociates into ions in aqueous solutions

Question 4

how does the strength of an acid/base link to equilibrium?

Answer 4

• the weaker the acid/base, the less it dissociates and the more the equilibrium lies to the left

Question 5

what is the equation for Kw in pure water and why?

Answer 5

Kw = [H⁺]²
- in pure water, the concentration of hydrogen ions is equal to the concentration of hydroxide ions

Question 5

what is an amphoteric substance

Answer 5

• a substance that can act as both an acid and a base

Question 6

what is Kw and what is its value at 298K

Answer 6

• Kw is the ionic product of water
• at 298K, Kw = 1x10⁻¹⁴mol²dm⁻⁶

Question 6

what equation links pH and the concentration of hydrogen ions?

Answer 6

pH = -log₁₀[H⁺]

Question 7

How to work out [H⁺] from pH

Answer 7

[H⁺] = 10⁻ᵖᴴ

Question 7

what is the equation for Kw

Answer 7

Kw = [OH⁻][H⁺]

Question 8

how to calculate the dilution of a strong acid

Answer 8

• calculate the moles of H⁺
• convert to conc by dividing by volume
• pH = -log₁₀[H⁺]

Question 9

how to calculate the dilution of a strong base

Answer 9

• calculate moles of OH⁻
• convert to conc by dividing by new volume
• Kw/[OH⁻]=[H⁺]
  -pH = -log₁₀[H⁺]

Question 10

how to calculate the pH of mixtures of strong acids and bases

Answer 10

• calculate the moles of H⁺
• calculate moles of OH⁻
• work out whats in excess
• convert to concentration by dividing by volume
• use Kw = [OH⁻][H⁺] equation if OH in excess
• -pH = -log₁₀[H⁺]

Question 11

what is the equation for Ka and what are its units?

Answer 11

• Ka = [H⁺][A⁻]/[HA]
• moldm⁻³

Question 12

how does the Ka value correlate with equilibrium

Answer 12

• larger the Ka value, the further the equilibrium is to the right

Question 13

how does the Ka value correlate with the strength of the acid

Answer 13

• higher the Ka value , the stronger the acid

Question 14

what equations links pKa with Ka

Answer 14

• pKa = -logKa
• Ka = 10⁻ᵖᴷᵃ

Question 15

what does Ka = for most weak acids and why

Answer 15

• Ka = [H⁺]²/[HA]
• since the acid barely dissociates, HA barely changes at eq and [H⁺] = [A⁻] as the molar ratio is 1:1