Desk Name Date Laboratory Instructor Pre-lab Titration Curves of Polyprotic Acid

Question

Desk Name Date Laboratory Instructor Pre-lab Titration Curves of Polyprotic Acids Questions Before beginning this experiment in the laboratory, you should be able to answer the following questions. 1. What is a polyprotic acid? If 10.70 mL of 0.105 M NaOH is required to reach the first equivalence point of a solution of citric acid (H,C,H,O), how many milliliters of NaOH are required to completely neutralize this solution? 2. 3. How many millimoles of NaOH will react completely with 50 mL of 1.5 MH,C20, 4. How many moles of H,O' are present in 250 mL of a 0.30 M solution of H SO4? 5. Why is it necessary to standardize a pH meter? 6. If the plH at one-half the first and second equivalence points of a dibasic acid is 4.20 and 7.34, respectively, what are the values for pK and pKa? From pkal and pkaz. calculate the Kat and K2 137

Explanation / Answer

1) polyprotic acid is an acid which gives out more than one proton or hydrogen atom per molecule when dissolved in water.

2) H3C6H5O7 ( citric acid) is a polyprotic acid which can give 3 hydrogen atom in aqueous solution. So if for 1 equivalence point, that is to neutralise one hydrogen atom completely it requires 10.7ml NaOH, for three hydrogen it will require 3×10.7= 32.1ml of NaOH are required.

3) since H2C2O4 is a diprotic acid, it will require 2(50×1.5)= 150 millimoles of NaOH to completely react with H2C2O4.

4) since one mile of H2S2O4 will give out two mole of H3O+ (H+), therefore 0.25×0.30 moles of H2S2O4 will give 2×0.25×0.30 moles of H3O+ which is equal to 0.15.

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