In the pH titration, why was it necessary to continue to take pH data points sev

Question

In the pH titration, why was it necessary to continue to take pH data points several milliliters of titrant beyond the equivalence point of the titration? Assume that a student performs a pH titration to determine the molar mass of an unknown weak acid. The student uses poor lab practice by writing down the mass of his unknown sample on a piece of paper towel and then copies down the value incorrectly onto his data page. The actual mass of the sample was 0.2145 g. He mistakenly wrote down 0.1245 g. but otherwise performed the experiment correctly. What effect, if any, will this have on the molar mass of the unknown acid (too high, too low. or no effect)? Explain why.

Explanation / Answer

This is for calculatation of exact volumes (equivalent point) of the titrant that have to be added to the solution to change indicator color.

Even if we are on the other side of the equivalence point, situation is similar - when we start to observe color changes, we are on the steep part of the curve, so small amounts of titrant added dramatically change pH of the solution.

So, from these plots it is obvious that when we stop titration seeing color change, we are close to the equivalence point, however we have added stoichiometric amount of the titrant, so we have to add excess of the titrant. That means we may expect a negative error or positive error, to omit that we required to add more volume.

Molarity = w/MW *1000/V

Molecular Weight = w/M x 1000/V

Hence if weight is given wrongly in lower side, then the Molecular weight also will too low

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