Question

A compound is formed when 12.2 g Mg combines completely with 5.16 g N. What is the percent composition of this compound? Please show all work and include the percentage of both magnesium and nitrogen.
Calculate the percent by mass of carbon in CO2 (carbon dioxide). Please show all work.

Answer 1

3Mg + N₂ → Mg₃N₂
n(Mg) = 12,2g÷24,4g/mol = 0,5mol - limiting reagente.
n(N₂) = 5,16g÷28g/mol = 0,18mol
n(Mg₃N₂):n(Mg) = 1:3, n(Mg₃N₂) = 0,166mol
m(Mg₃N₂) = 0,166mol·101,2g/mol = 16,8g.
%(N)= 2·Ar(N)÷Mr(Mg₃N₂) = 2·14÷101,2 = 27,66% = 0,2766
%(Mg) = 3·Ar(Mg)÷Mr(Mg₃N₂) = 3·24,4÷101,2 = 72,34%
              or 100% - 27,66% = 72,34%.