Question

One atomic mass unit in $amu=1.66\times {10}^{-27}kg$. The atomic weight of oxygen is 16. The mass of one atom of oxygen is?

(A) $26.56\times {10}^{-27}kg$
(B) $10.53\times {10}^{-27}kg$
(C) $74\times {10}^{-27}kg$
(D) $2.73\times {10}^{-27}kg$

Answer 1

Hint: The atomic weight of oxygen is given in $$amu$$. The conversion factor relating $$amu$$ and kg: $1amu=1.66\times {10}^{-27}kg$. Multiply the atomic weight with the value to get the mass of one atom of oxygen.

Complete step-by-step solution

Atomic mass unit ($$amu$$): In nuclear physics a convenient unit of mass is the unified atomic mass unit abbreviated as $$amu$$. It is sometimes also denoted by u.

Atomic mass unit is defined as one- twelfth ($${\displaystyle \frac{1}{12}}th$$) the mass of a carbon – 12 ($${}_6{C}^{12}$$ ) atom.

It is given that the atomic weight of oxygen$$n=16$$ $$amu$$. The mass of one atom can be calculated using the given relation,$1amu=1.66\times {10}^{-27}kg$

Therefore, the mass of one atom of oxygen is

$$\begin{gathered} 16\times 1.66\times {10}^{-27} \\ =26.56\times {10}^{-27}kg \end{gathered}$$
Mass of one atom of oxygen is $26.56\times {10}^{-27}kg$

the correct option is A.

Note: Mass of electron $$=9.1\times {10}^{-31}kg=0.0005486amu$$

Mass of proton $$=1.6726\times {10}^{-27}kg=1.007276amu$$

Mass of neutron $$=1.6750\times {10}^{-27}kg=1.00865amu$$

Atomic mass unit is also associated with energy in terms of$$MeV$$, from the Einstein’s mass energy equation $$E=m{c}^2$$ where$$,1amu=931MeV$$.