Question

For standardization of 0.1M HCl solution with NaOH. the procedure is as follows: The Burette has the 0.1M NaOH solution, and using a pipette, pipette 30mL of 0.1M HCl into an appropriatly sized flask, add phenolphthalein and then titrate. If the pipette was wet when you started to use it, how would your results be affected if: a) it was wet with distilled water b)it was wet with NaOH c) it was wet with 1M HCl d) it was wet with 0.1M HCl

Answer 1

a) If the pipette was wet with distilled water, the concentration of the HCl solution in the flask added from the pipette will be lower than 0.1 M HCl. Therefore, smaller amount of 0.1 M NaOH solution will be required to titrate it and see the expected color change for phenolphthalein. Hence the observed concentration of the acid solution will be found lower than actual concentration.

b) If the pipette was wet with NaOH, then some of the HCl added in the pipette will get neutralized before adding to the flask. Once again, smaller amount of 0.1 M NaOH solution will be required to titrate it and see the expected color change for phenolphthalein. Hence the observed concentration of the acid solution will be found lower than actual concentration.

c) If the pipette was wet with 1 M HCl, the overall solution after adding 0.1 M HCl using this pipette will have higher concentration of HCl than 0.1 M. Therefore, more 0.1 M NaOH solution will be required to neutralize it compared to a solution with actual HCl concentration of 0.1 M. Hence the observed concentration of the acid solution will be found higher than actual concentration.

d) If the solution was wet with 0.1 M HCl, then the solution in the flask added from the pipette will also have HCl concentration of 0.1 M. Therefore in this case, the right amount of 0.1 M NaOH will be required to neutralize the acid solution and the observed concentration will be accurate.