Question

# Calculate the mass of $0.5 moles$ of helium gas. (Atomic mass of $He = 4u$ )

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Hint: The mass of $0.5 moles$ of helium gas can be calculated by the relation between mass, moles and Atomic mass of Helium gas. We should remember the relation between these quantities moles is equal to the mass divided by molar mass.

Formula used:
$moles = \dfrac{{mass}}{{molar mass}}$

In the given question we have given the moles of helium gas and Atomic mass of helium gas that is $0.5$ and $4u$ respectively. We have to calculate the mass of helium gas. By using the above formula we can calculate the mass of Helium gas.
$moles = \dfrac{{mass}}{{molar mass}}$
$0.5 = \dfrac{{mass}}{4}$
$mass = 2g$
Hence, the $2g$ mass of helium gas is present in $0.5moles$.
Atomic mass: It is defined as the mass of an atom of a particular substance. It is also defined as the total number of neutrons and protons present in an atom known as atomic mass. For example let us consider an atom namely sodium which has $2$ protons and $2$ neutrons are present in it. Hence the atomic mass of sodium is $4$ .
Note:A mole is defined as $6.02214 \times {10^{23}}$ of some chemical unit, be it atoms, molecules, ions, or other. The mole is a convenient unit to use because of the great number of atoms, molecules or other in any substance. The mole was originally defined as the number of atoms in $12gram$ of carbon-$12$ .