Oceans - Buffer solutions
10 important questions on Oceans - Buffer solutions
Why does a solution of a weak acid not act as a buffer solution?
A weak acid has a large amount of undissociated acid (proton donor) but a very small amount of the base ion (proton acceptor) = the pH will change a lot with small additions of acid or alkali
What are the two assumptions of Ka?
1. all the anions (A-) come from the salt, so the contribution from the acid is negligible
2. the concentration of the acid in solution [HA (aq)] is the same as the amount put into the solution
A 0.010moldm-3 solution of GHB has a pH of 2.9. Calculate the value of Ka for the GHB & give its units.
Ka = [H+][A-] / [HA]
Ka = [H+][A-] / 0.010
pH = -log[H+]
[H+] = 10^-2.9
Ka = (10^-2.9)^2 / 0.010
Ka = 1.58 x 10^-4
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Why are buffer solutions found in our bodies?
To maintain pH in the body so enzymes & reactions in the body can take place.
Using the equation and Le Chatelier's principle, explain why CO2 is more soluble in water at greater depths.
CO2 (aq) *double headed arrow) CO2 (g)
More gaseous molecules on the RHS so the eqm moves to the LHS. The pressure is higher at greater depths (+ lower temp) so more CO2 is produced
What, in the ocean, can help to remove CO2 from the atmosphere? What problem is created by this?
Liquefying the gas under pressure in natural trenches on the sea floor BUT this may disturb the ocean's eco-system.
What do buffer solutions contain?
- either a weak acid and one of its salts e.g. ethanoic acid and sodium ethanoate
- or a weak base and one of its salts e.g. ammonia and aluminium chloride
What abbreviations can be made to the formula of Ka and Kw?
Ka = [H+] / [HA]
Kw = [H+][OH-]
Suggest why the presence of a buffer solution helps preserve food by preventing enzymic reactions.
Each enzyme reaction occurs at a specific pH. The buffer will maintain a pH where the reaction could not work (a change in pH changes the shape of the active site)
Describe what is meant by the term 'buffer solution' and explain how a buffer works based on the equilibrium. *always comes up in exams*
A solution which can withstand changes in pH despite the addition of small amounts of acid or alkali. With the addition of H+/ acid the equilibrium moves to the LHS in order to counteract this change because H+ will react with A-. With the addition of an alkali the equilibrium moves to the RHS to generate the H+ ions. This is because buffer solutions are made of a weak acid and its salt which provides a reservoir of A- ions.
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