Question

Unit 4 Assignment Ilse the following additional information to answer the next part of the question A technician uses the 500.0 ml. of 0.100 mol/L acetic acid to prepare an acetic acid sodium acetate buffer solution. She does this by adding 0.100 mol/L sodium acetate to the 0.100 mol/L acetic acid until the required pH is reached. Identify the shift in equilibrium that will occur when sodium acetate is added to the equilibrium reaction. Predict whether or not there is an effect on the equilibrium constant and if so, what the effect on the equilibrium constant is. (2 marks) If small quantities of aqueou solution, predict whether the solution will change or stay th S of aqueous sodium hydroxide are added to the buffer whether the pH of the acetic acid-sodium acetate bun change or stay the same. Explain your answer. (2 marks)

Answer 1

aus. b Solution of acilic acid and soduim acetate is a buffer. Equilibruim reaction in buffer is: CH₂ 2001 (aq) + H₂0 (1) 2 H₂O + (aq) + CH₃W 0 (af) When so duim acetate is added to buffer then the concentration of acetate increases, so the equilib ruim will move to the left i.e, more Ch₂200h will be formed to balance. There will be no effect on equilibruim constant It will remain unchanged. 1 K,= [CH3 60}[H3ot) [uuzwon] Since if [CH₂ wol is increased reaction will move in a way to increase anount of CCH₂ cook] and decreare amount of LC41360). Moreover equilibrum constant do not change with change in concentrations, it only change with change in temperature. Only position of equilibruim changes on changing concentration.

& winen NaOH is added to buffer solution , there will be very little increase in ph, it almost remains the same. Buffer equilibrium CH₂COOH + H₂O = CH₂ Wolaq.) + Hz otlaq.) Naoh is added then the equilibrium shifts to right as follows CH3COOH (aq) + oH → H₂O (1) + CH3co o cag.) It can be seen that on addition of base the equilibrium moves to the right making up for loss of hydrogen con in reaction with the base. pH almost remarins same on addition of small amount of base.