Question

The molar mass of a solid carboxylic acid is determined by titrating a known mass of the acid with a standardized solution of NaOH to a phenolphthalein endpoint. Which errors will lead to a molar mass that is smaller than the actual molar mass? I. Some of the acid is spilled when being transferred into the titration flask. II.The endpoint is recorded when the solution is dark red in color rather than light pink.

Answer 1

The answer is: II.The endpoint is recorded when the solution is dark red in color rather than light pink.

The endpoint is the point at which the indicator changes colour in a colourimetric titration and that is point when titration must stop.  

Phenolphthalein is colorless in acidic solutions and pink in basic solutions. If  this indicator change color to dark red, more base is added and endpoint is not accurate.

If the the acid is spilled before titration, that does not make endpoint wrong and molar mass can be calculated.

In this example we can take acetic acid as carboxylic acid; basic salt sodium acetate CH₃COONa is formed from the reaction between weak acid (in this example acetic acid CH₃COOH) and strong base (in this example sodium acetate NaOH).  

Balanced chemical reaction of acetic acid and sodium hydroxide:  

CH₃COOH(aq) + NaOH(aq) → CH₃COONa(aq) + H₂O(l).  

Neutralization is is reaction in which an acid (in this example vinegar or acetic acid CH₃COOH) and a base react quantitatively with each other.