CHXI01:SOME BASIC CONCEPTS OF CHEMISTRY
306832
What is the percentage of carbon in urea?
\({\rm{(Atomic}}{\mkern 1mu} {\mkern 1mu} {\rm{mass}}{\mkern 1mu} {\mkern 1mu} {\rm{C = 12,}}{\mkern 1mu} {\mkern 1mu} {\rm{H = 1,}}{\mkern 1mu} {\mkern 1mu} {\rm{N = 14,}}{\mkern 1mu} {\mkern 1mu} {\rm{O = 16)}}\)
1 \({\rm{20\% }}\)
2 \({\rm{26}}{\rm{.6\% }}\)
3 \({\rm{6}}{\rm{.67\% }}\)
4 \({\rm{46}}{\rm{.0\% }}\)
Explanation:
Molar mass of urea \({\rm{(i}}{\rm{.e}}{\rm{.}}{\mkern 1mu} {\mkern 1mu} {\rm{N}}{{\rm{H}}_{\rm{2}}}{\rm{CON}}{{\rm{H}}_{\rm{2}}}{\rm{)}}\)m
\[\begin{array}{l}{\rm{ = 2 \times atomic}}{\mkern 1mu} {\mkern 1mu} {\rm{mass}}{\mkern 1mu} {\mkern 1mu} {\rm{of}}{\mkern 1mu} {\mkern 1mu} {\rm{N + 4 \times atomic}}{\mkern 1mu} {\mkern 1mu} {\rm{mass}}{\mkern 1mu} {\mkern 1mu} {\rm{of}}{\mkern 1mu} \\
{\mkern 1mu} {\rm{H + 1 \times atomic}}{\mkern 1mu} {\mkern 1mu} {\rm{mass}}{\mkern 1mu} {\mkern 1mu} {\rm{of}}{\mkern 1mu} {\mkern 1mu} {\rm{O + 1 \times atomic}}{\mkern 1mu} {\mkern 1mu} {\rm{mass}}{\mkern 1mu} {\mkern 1mu} {\rm{of}}{\mkern 1mu} {\mkern 1mu} {\rm{C}}\end{array}\]
\({\rm{ = 2 \times 14 + 4 \times 1 + 1 \times 16 + 1 \times 12 = 60}}{\mkern 1mu} {\mkern 1mu} {\rm{g}}\)
As we know that,
Percentage or mass % of an element
\({\rm{ = }}\frac{{{\rm{Mass}}{\mkern 1mu} {\mkern 1mu} {\rm{of}}{\mkern 1mu} {\mkern 1mu} {\rm{that}}{\mkern 1mu} {\mkern 1mu} {\rm{element}}{\mkern 1mu} {\mkern 1mu} {\rm{in}}{\mkern 1mu} {\mkern 1mu} {\rm{the}}{\mkern 1mu} {\mkern 1mu} {\rm{compound}}}}{{{\rm{Molar}}{\mkern 1mu} {\mkern 1mu} {\rm{mass}}{\mkern 1mu} {\mkern 1mu} {\rm{of}}{\mkern 1mu} {\mkern 1mu} {\rm{the}}{\mkern 1mu} {\mkern 1mu} {\rm{compound}}}}{\rm{ \times 100}}\)
\(\therefore {\mkern 1mu} {\mkern 1mu} {\rm{Percentage}}{\mkern 1mu} {\mkern 1mu} {\rm{of}}{\mkern 1mu} {\mkern 1mu} {\rm{C = }}\frac{{{\rm{1 \times 12}}}}{{{\rm{60}}}}{\rm{ \times 100 = 20\% }}\)