Question

What mass of nitrogen are there in $50.0g$ samples of sodium nitrate $(NaN{O_2})$ ?
a. $20.2g$
b. $16.4g$
c. $10.1g$
d. $8.23g$
e. $23.4g$

Answer 1

Hint: The measure of amount in an object known as mass. Mass is normally measured in grams and kilograms. Mass in a compound is the sum of the mass of the all atoms, which are present in the compound.

Complete step by step answer:
Atomic mass is the sum of protons or neutrons in an atom. To calculate the mass of given compound there are three ways:
By referring to the periodic table:
See the atomic number in the periodic table, mass is normally marked under the representation of an element.
Addition of Mass of Protons and Neutron:
Mass of a compound or atom can be calculated by the sum of the protons and neutrons present in the compound or atom.
All atoms of an element - Average weight:
The mass can be calculated by the average of all three isotopes. If isotopes abundance is present in the compound it must be divided by the 100.

We have calculated the mass of the $(NaN{O_2})$ using the referring of the periodic table.

${\rm{Molecular\; weight \;of }}NaN{O_2} = [23 + 14 + (162)] = 69g$

Amount of Nitrogen in 69g of $NaN{O_2} = 14g$

69g $NaN{O_2}$ contain 69 g of N

$\therefore 1g{\;\rm{ of }}\;NaN{O_2}{\;\rm{ contain }}\dfrac{{14}}{{69}}g{\;\rm{ of N}}$

${\rm{Thus, \;50g }}\;NaN{O_2}{\rm{ will \;contain }}\dfrac{{14}}{{69}} \times 50g{\rm{ \;of\; N,\; that \;is }}10.1g$

So, the correct answer is Option c.

Note: The formula to calculate the mass is
Atomic mass = Mass of protons + Mass of neutron + Mass of electron. The unit of the atomic mass is different from the total mass of a compound. But there are some elements whose mass cannot be determined by the second method, it can be calculated only by the average weight. Ex. Calcium, chloride, Magnesium, Potassium etc. these are the exception.