Why should enough solid KHT be added Jo the KCl-NaCl solution to ensure that som

Question

Why should enough solid KHT be added Jo the KCl-NaCl solution to ensure that some solid remains dissolved after the 20-min stirring? Why should you make sure that the beaker, funnel, and filter paper arc dry before you begin to filter the saturated KHT solution? Prior to the titration with NaOH solution, you will add a measured volume of the filtered saturated KHT solution to an Erlenmeyer flask. Is it necessary that this flask be dry? Briefly explain. In an experiment similar to this one, the solubility of potassium hydrogen oxalate (KHC_2O_4, molar mass = 128.13 g mol^-1) is determined. A 5.0 10^-2 M aqueous solution of KCl is saturated with potassium hydrogen oxalate. The following equilibrium results: KHC_2O_4(s) K^+ (aq) + HC_2O_4^- (aq) Following saturation, the solution is filtered Portions of the filtered saturated solution are titrated with 0.1172M NaOH solution.

Explanation / Answer

2. KHT has K ions in common with KCl - NaCl solution. This reduces the solubility of KHT due to common ion effect. So, in order to make a saturated solution of KHT we must add enough KHT solid to the solution and stir ensuring some amount of KHT remains undissolved at the bottom even after stirring for 20 minutes. The upper supernatent solution would become saturate KHT solution.

3 a) The beaker, funnel and filter paper must be dry before filtering out the saturated KHT solution in order to make sure that the actually solution doesnt get contaminated or diluted.

b) The flask must be dry. If it has minor amounts of water then that would dilute the KHT solution and lead to miscalculation of the volume of NaOH required for the titration with KHT.

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