A binary compound contains only magnesium and nitrogen
CHEMISTRY · Single correct · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties
Problem
A binary compound contains only magnesium and nitrogen. If an analysis reports that the compound is 60.3 % magnesium by mass, which statement best explains why the mass percentage of nitrogen must be 39.7 %?
(a) Because the empirical formula of magnesium nitride is Mg3N2, the compound contains three magnesium atoms for every two nitrogen atoms, so nitrogen’s mass percentage is 52×100%≈39.7%.
(b) Because the ratio of the molar masses 24.3:14.0 for Mg:N simplifies to about 60:40, nitrogen must contribute the remaining 39.7% of the compound’s mass.
(c) Because a compound that consists of exactly two elements must have mass percentages that sum to 100%, so the remaining 39.7% must correspond to nitrogen.
(d) Because converting 60.3% magnesium to moles (60.3/24.3) and then multiplying by nitrogen’s molar mass gives about 39.7%, which represents nitrogen’s percent by mass.