Question

Monitosing.Acid-Base Titrations wih a pH Meter 3. student titrated 20.0 mL of 0.410M HCI with 0.320M NaOH and collected the following data. Pre-Laboratory Assignment 1. Briefly explain: (a) why you must use caution when with HCI solutions 0.32 A working volume NaOH solution added, mLpH 0.39 0.46 0.54 0.62 0.70 0.78 0.87 0.96 1.07 1.19 1.35 1.56 1.93 2.09 2.35 3.06 11.40 11.80 12.00 12.20 12.30 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00 24.00 24.50 25.00 25.50 26.00 26.50 27.00 28.00 29.00 (b) what you will do with the NaOH solution re- maining in your buret after you have completed your titrations. 2. Calculate [H3O'] and [OH'1 in solutions of (a) pH 4.18 (b) pH 5.70 (c) pH 8.56 (a) Prepare a titration curve for this titration. (b) Identify the volume of titrant required to reach the equivalence point of the titration. (c) What are the pH, [H30'1, and [OH ] when 21.50 mL of titrant has been added?

Answer 1

Answer 1

a) Caution must be used while working with HCl because, HCl solution is acidic in nature and hence is corrosive to skin and eyes. Moreover, when used as concentrated solution, the HCl gas keeps on evolving which is irritating eyes, nose and respiratory tract.

b) After completion of experiment, left over NaOH must be disposed off properly. It should not be decanted off in sink. Rather, it should be collected in a beaker, few drops of phenolphthalein must be added to it and then it should be neutralized using left over HCl or any other acid. But the addition of acid must be slowly or dropwise till the pink color gets discharged. This neutralized solution can then be safely decanted off in the sink.

Answer 2

pH = -log[H₃O⁺] or [H₃O⁺] = 10^-pH

Also, [H₃O⁺] [OH^-] = 1 x 10^-14 or [OH^-] = (1 x 10^-14)/[H₃O⁺]

So, using above two formulae, we can fill up the table

	[H3O+]	[OH-]
pH = 4.18	10-4.18 = 6.7 x 10-5 M	1.5 x 10-10 M
pH = 5.70	10-5.70 = 2 x 10-6 M	5 x 10-9 M
pH = 8.56	10-8.56 = 3x 10-9 M	3.33 x 10-4 M