A student plots the mass of a pure crystalline solid versus the amount in moles and…
CHEMISTRY · Single correct · A Level · Chemistry · Amount of substance · Amount of substance
Problem
A student plots the mass m of a pure crystalline solid versus the amount in moles n and obtains a straight line that passes through the origin. Which of the following best explains why the numerical value of the slope of this line equals the substance’s molar mass?
(a) Because the line passes through the origin, its slope must represent the substance’s density in gcm−3.
(b) Because mass and amount are directly proportional, and the proportionality constant has units of g mol−1.
(c) Because Avogadro’s number is the same for all substances, it cancels out any dependence on particle mass, leaving the slope equal to the molar mass.
(d) Because one atomic mass unit is defined relative to grams, the slope automatically converts grams to atomic mass units, so its value equals the atomic or molecular mass.