(1) A student weighs 0.347 g of KHP on a laboratory balance. The KHP was titrate
ID: 481366 • Letter: #
Question
(1) A student weighs 0.347 g of KHP on a laboratory balance. The KHP was titrated with NaOH and the concentration of the NaOH determined to be 0.110 M. For the second titration, the student correctly diluted 6 M HCl from the reagent shelf using a graduated cylinder to obtain approximately 0.6 M HCl. This solution was titrated with the original NaOH solution. The student calculated the concentration of NaOH from the experiment to be 0.099 M. In which experiment should the student be more confident of the concentration of the NaOH solution? Why?
(2) A student is given a dilute solution of a strong base and a solution of a weak base of unknown concentration. If each solution is titrated with a standard solution of HCl(aq); how would you distinguish between the two different solutions?
(3) A student needed to standardize a 0.1 M solution of NaOH. The student transferred 25 mL of NaOH solution into an Erlenmeyer and carefully started the titration with a 0.20 M solution of HCl. The student did not see any color change after adding 50.0 mL of HCl. What could be the source of error in this experiment?
Explanation / Answer
(1) Method with KHP is more accurate because, we have accurately known the concentration of KHP, as we have weighed the required amount. The original concentration of 6 M HCl is not accurately known. It may have happend that we have prepared 6 M HCl solution long ago and the concentration might have changed over a period of time.
(2) When we titrate strong base with strong acid, we get rapid/sharp colour change at the end point. When we titrate weak base with strong acid, we get gradual colour change at the end point.
(3) No indicator was added. So no colour change will be observed.
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