Question

You will need the answer tio question 2 during the experiment.

1) At the endpoint of a titration, the color of the solution should be (a)bright pink, (b) pink, (c) faint pink, (d) colorless ?

2)We will calculate the amount of acid to use in each titration. Assume that you are using 0.0512 M NaOH (aq). A good violume of NaOH(aq) to use per titration is 15ml, From this molarity and volume, the moles of NaOH can be calculated. Since the unknown acid is monoprotic, this also equals the number of moles of a acid to use. A typical molar mass for an unknown acid in this experiment is 380g/mol. Using the molar mass, calculate the mass (in grams) of an unknown acid you should use per titration. (round to the nearest 2 sig figs)

3) Suppose that 10.4ml of 0.0512 M NaOH were required to titrate a sample of unknown acid. How many moles of NaOH were used?

4) Assuming that the unknown acid sample in question 3 had a mass of 0.177g, what is the molar mass of the unknown acid?

Answer 1

1) The correct answer is (c). At the end point of weak acid-strong base titration, the pH of solution is alkaline(greater than 7), hence phenolphthalein indicator is used. Phenolphthalein gives faint pink color at the endpoint of the titration.