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

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 ($\dfrac{1}{12}th$) the mass of a carbon – 12 ($_6{C^{12}}$ ) atom.

It is given that the atomic weight of oxygen$n{\text{ }} = {\text{ }}16$ $amu$. 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

$
16 \times 1.66 \times {10^{ - 27}} \\

= 26.56 \times {10^{ - 27}}kg \\

$Mass of one atom of oxygen is$26.56 \times {10^{ - 27}}kg$

the correct option is A.

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

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

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

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