Question

The mass of one amu is approximate?
A. 1g
B. 0.5gF
C. $1.67\text{ }\times \text{ 1}{{\text{0}}^{-24}}g$
D. $\text{3}\text{.2 }\times \text{ 1}{{\text{0}}^{-24}}g$

Answer 1

amu stands for the Atomic Mass Unit. The amu is defined as the 1/12th mass of the carbon atom. One mole of any substance is equal to the Avogadro's number of $6.022\text{ }\times \text{ 1}{{\text{0}}^{23}}$particles that can be electron, atom, proton, etc.

Complete answer:
-The 1/12th mass part of the carbon is considered as the stable isotope to compare the mass of the other elements because the number of protons and neutrons do not change under several conditions.
-Carbon consists of six protons and six neutrons in the orbital.
-To calculate the mass of one amu, we know that the mass of one amu will be equal to the 1.12th part of the mass of the carbon -12 atom.
-So, firstly we have to calculate the mass of the carbon -12 atom. As we know that $6.022\text{ }\times \text{ 1}{{\text{0}}^{23}}$atoms are present in the 12g so the mass of the carbon will be:
$\dfrac{\text{No}\text{. of atoms }}{6.022\text{ }\times \text{ 1}{{\text{0}}^{23}}}\ \text{= }\dfrac{\text{Mass}}{\text{Molar mass}}$
$\dfrac{\text{1 }\times \text{ 12}}{6.022\text{ }\times \text{ 1}{{\text{0}}^{23}}}\ \text{= Mass}$
So, the mass will be $1.99\text{ }\times \text{ 1}{{\text{0}}^{-23}}$
-Now, we know that the value of one AMU is equal to the $\dfrac{1}{12}\text{ }\times \text{ Mass of the C-12}$
-So, the one amu = $\dfrac{1}{12}\text{ }\times 1.99\text{ }\times \text{ 10}{{\text{ }}^{-23}}\text{ = 1}\text{.67 }\times \text{ 10}{{\text{ }}^{-24}}$g.

Therefore, option C is the correct answer.

Note: Atomic mass unit is used for the atoms and the subatomic particles because they have very small mass and amu is a convenient unit to express the mass. One AMU is also equal to the average rest mass of the proton and neutron. The electron's rest mass is the mass of the electron when it is present in the stationary state.