3. Consider how each of the situations described below would affect the experime

Question

3. Consider how each of the situations described below would affect the experimental value determined for the molecular weight of an unknown solid acid. Explain why the experimental molar mass would be too large, too small, or unaffected because of the situation described. c. The student always uses the same malfunctioning balance which is weighing everything exactly 0.0100 grams too light. d. The unknown acid is contaminated with solid sodium chloride. e. In part B of the experiment, the student assumes that KHP is a diprotic acid when calculating the molarity of the NaOH.

Explanation / Answer

Influence of experimental error on molecular weight determination,

c. If the student weighs everything exactly 0.01 g too light, the observed molar mass would remain the same. Since everything changes consistently, the grams and moles would remain same and so molar mass would be unchanged.

d. The unknown acid is contaminated with sodium chloride : The observed molar mass would be higher than actual value. Again, molar mass is directly related to amount of substance taken, that is molar mass = g/moles. As moles by experiment would be lower, the molar mass would be higher.

e. In part B of the experiment, the student assumes that KHP is a diprotic acid when calculating the molarity of NaOH. In this case the molarity of NaOH calculated would be 1/2 of actual value so the moles of acid would also becomes half. This would increase the molar mass. Thus observed molar mass would be higher than actual value.

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