Acids, Bases and buffers Flashcards
What is a Brønsted-Lowry reaction?
Reaction involving the transfer of a proton
What is a Brønsted-Lowry acid
Proton donor
What is a Brønsted-Lowry base ?
Proton acceptor
What is the definition of pH ?
pH = -log[H]
How do you rearrange pH to find the concentration of H+ ions ?
[H+] = 10^pH
What is the ionic product of water (Kw) ?
Kw =[H] [OH]
How does temperature affect the pH of water ?
H2O ≠ H + OH
- As temperature increases, the equilibrium moves to the right to oppose the increase in temperature becoming slightly more acidic
- water is still neutral though because [H] = [OH]
What is the pH of pure water at 25º ?
7
- because [H] = [OH]
How would you calculate the pH of pure water ?
1) in pure water Kw = [H]^2
2) rearrange so that [H] = √Kw
3) pH = -log [H]
Suggest why pure water at 10ºC is not alkaline
Because there are equal concentrations of H+ and OH-
What are the steps in calculating the pH of a strong base?
1) identify OH- concentration via c x v = n
2) use Kw to find [H] concentration
3) calculate pH
Explain why a weak base weak acid reaction could not be titrated using an indicator ?
Because the equivalence point would be difficult to distinguish
Predict whether the pH of the magnesium hydroxide solution formed at 10 °C is
larger than, smaller than or the same as the pH of the calcium hydroxide
solution at 10 °C
Ph of magnesium hydroxide will have a lower pH compare to Calcium hydroxide which would be more basic as it is more soluble and will dissociate further than Mg(OH)2
What steps are involved in calculating the pH of a mixture of acid and base ?
1) calculate moles of [H]
2) calculate moles of [OH]
3) write equation and find XS [H] or use Kw to find XS [OH]
4) calculate pH = -log[H]
What is Ka ?
Acid dissociation constant
Ka = [H] [OH] / [HA]
Used for weak acids
How to find Ka ?
pKa = -log Ka
Ka= 10-pKa
What is the relation between Ka value and the strength of the acid ?
The bigger the Ka the stronger the acid
The smaller the pKa value the stronger the acid
Ka for weak acids ?
Ka = [H]^2 / [HA]
How is a buffer solution made ?
React less moles of the base than the acid to ensure there will be excess acid as well as the salt
How does a buffer solution resist pH change ?
The OH- salt ion reacts with the H+ ions to remove them
