Question

What is the mass $$ of H in ${{C}_{9}}{{H}_{10}}{{N}_{2}}$?

Answer 1

The atomic masses of the required atoms are given as C= $12$, H= $1$, N= $14$
Molar mass of a substance = No of moles of substance * atomic mass of the substance
Mass Percent of an atom in a compound is the percent composition of the atom in the compound.

Complete answer:
It is given by the formula $\dfrac{\cdot ~~~~~~No.\text{ }of\text{ }moles\text{ }of\text{ }the\text{ }substance*atomic\text{ }mass*100}{total\text{ }mass\text{ }of\text{ }compound}$ i.e., the total mass of the substance in the given compound divided by the total mass of the compound.
We have to calculate the total mass of the compound i.e., no. of moles of Catomic mass of C + No. of moles of H * atomic mass of H + No. of moles of N atomic mass of N.
According to the formula, Total mass of the compound =$9*Atomic\text{ }mass\text{ }of\text{ }C+10*atomic\text{ }mass\text{ }of\text{ H+2* }atomic\text{ }mass\text{ }of\text{ N}$
No. of moles of C $=9$
No. of moles of H $=10$
No. of moles of N $=2$
Atomic mass of C$=12$
Atomic mass of H $=1$
Atomic mass of N $=14$
To obtain the total mass of the compound, we need to multiply the mass of each atom with the number of atoms in the given formula.
Hence substituting the values:
Total mass of compound =$9 \times 12+10 \times 1+2 \times 14$
Total mass of compound = $108+10+28$
Total mass of compound $=146$
No. of moles of Hydrogen in {{C}_{9}}{{H}_{10}}{{N}_{2}}$$$$=10
Putting the values in the formula mentioned above:

∴ Mass $∴ Mass Hence the mass${{C}{9}}{{H}{10}}{{N}_{2}}$$ is $6.849$%

Note:
Mass percent is used to define the composition of a particular element in the given compound.
We can also use the Formula $\dfrac{\text{molar mass of the atom }\times \text{100}}{\text{total molar mass of the compound}}$ where molar mass is given by multiplying the no. of moles of atom in the compound by the atomic mass of the atom.