Buffers

• A buffer solution is a solution which resists change in pH when small amounts of acids or alkalis are added.
• HA + OH- → A- + H2O.
• pH = -log[H+],
• Ka = [H+] [A-] [HA], where 1.74 = 𝑥10-5 𝑥0.
• Ethanoic acid and sodium ethanoate can be used as a buffer, with the buffer solution containing relatively high concentrations of CH3COOH (due to partial ionisation of ethanoic acid) and CH3COO- (due to full ionisation of sodium ethanoate).
• When H+ ions are added to the buffer solution, the equilibrium position shifts to the left as H+ ions react with CH3COO- ions to form more CH3COOH until equilibrium is re-established.
• In the buffer solution, the ethanoic acid is in equilibrium with hydrogen and ethanoate ions.
• The H+ concentration decreases in the buffer solution when OH- ions are added.
• As there is a large reserve supply of CH3COO- in the buffer solution, the concentration of CH3COO- in solution doesn’t change much as it reacts with the added H+ ions.
• When OH- ions are added to the buffer solution, the OH- reacts with H+ to form water OH- (aq) + H+ (aq) → H2O (l).
• As a result, the pH remains reasonably constant in the buffer solution.
• As there is a large reserve supply of CH3COOH in the buffer solution, the concentration of CH3COOH in solution doesn’t change much as CH3COOH is formed from the reaction of CH3COO- with H+.
• The equilibrium position shifts to the right and more CH3COOH molecules ionise to form more H+ and CH3COO- until equilibrium is re-established.
• A buffer solution was made by adding 2.05 g of sodium ethanoate to 0.500 dm3 of 0.01 mol dm-3 ethanoic acid.
• A buffer can consist of a weak acid and its conjugate base, or a weak base and its conjugate acid.
• The pH of a buffer solution can be calculated using the Ka of the weak acid, the equilibrium concentration of the weak acid and its conjugate base (salt), and the concentration of hydrogen ions which can be found using the equilibrium expression.
• The pH of a buffer solution can be calculated using the formula K a = [ H + ] [ A − ] [ HA ], where K a is the acid dissociation constant, [H +] is the hydrogen ion concentration, [A −] is the alkali ion concentration, and [HA] is the hydronium ion concentration.
• The pH of a solution can be calculated using the formula K a = [ H + ] [ A − ] [ HA ], where K a is the acid dissociation constant, [H +] is the hydrogen ion concentration, [A −] is the alkali ion concentration, and [HA] is the hydronium ion concentration.
• The pH of a buffer solution can be calculated using the formula K a = [ H + ] [ A − ] [ HA ], where K a is the acid dissociation constant, [H +] is the hydrogen ion