Question

please answer all the parts

Supplemental Questions - Titration Lab, 1. Indicate how each of the following would affect the values of K, for the weak acid unknown and for the dibasic salt and the value of the molar mass for the dibasic salt (Would the determined values be higher or lower than the actual values?). Use larger, smaller or no change. And as always....Explain. a. The titrant (either the NaOH or the HCI) molarity is actually HIGHER than that stated on the label. b. The pH meter was incorrectly calibrated such that it reads 0.63 units too HIGH. c. The weak acid sample was impure, containing about 11% inert material. 2. Explain the difference between equivalence point and end point. Explain how the pH at the equivalence point varies as the strength of the acid increases. Remember that acid strength depends upon K, not upon analytical concentration. Your answer should be based upon the proton transfer reaction that is important at the equivalence point. 3. Explain the difference in change of pH with volume of titrant added near the equivalence point as compared to a point earlier in the titration (ie. How does the slope of the titration curve differ at each of these points?)

Answer 1

1

a) The Ka value depends on the temperature, nature of the acid, and the solvent , therefore Molarity will not affect the Ka value.

b) Ka value and pH has direct relation. So if the pH value is mismeasured to be high, then the reading for Ka value will also be high.

c) Weak acid sample was impure therefore it will dissociate less and therefore low Ka value.

2. The point where the mole of acid and base becomes equal during the titration is called equivalence point. And the point where the indicator changes it's color is called end point.

At the equivalence point the neutralisation is complete so the pH is 7. But if the strength of acid increase, in the proton transfer reaction occuring at end point will decrease the pH. Because the strength of acid is increasing.

3. At the equivalence point the pH is 7 because the neutralisation reaction us being completed.

But at the starting, if the titrant is base pH < 7 and if

Titrant is acid the pH > 7.