An analytical chemist investigates an unknown monoprotic organic acid
CHEMISTRY · Multi-part · A Level · Chemistry · Amount of substance · Amount of substance
Problem
An analytical chemist investigates an unknown monoprotic organic acid. Five separate samples are weighed and titrated, allowing the chemist to determine the exact number of moles of acid neutralised in each sample. The results are presented below.
Run
Mass of acid (g)
Amount n (mol)
1
0.450
0.00500
2
0.898
0.01000
3
1.345
0.01500
4
1.793
0.02000
5
2.238
0.02500
Use these data to answer the following questions.
(a) Determine the experimental molar mass of the acid from the data set and report the value to four significant figures.
(b) For each run, calculate the vertical deviation (in grams) of the experimental point from the best-fit line you used in part (a). Using these deviations, evaluate the precision of the measurements.
(c) Three possible identities for the acid are propionic acid (C₃H₆O₂, 74.08 g mol⁻¹), valeric acid (C₅H₁₀O₂, 102.13 g mol⁻¹), and caproic acid (C₆H₁₂O₂, 116.16 g mol⁻¹). Based on your experimental molar mass and precision analysis, select the most likely candidate and justify your choice.