Question

Calculate the weight in grams present in 0.7 moles of sodium
A) $16.1g$
B) $16.2g$
C) $16.3g$
D) $0.161g$

Answer 1

The mole is the unit of measurement for the amount of substance within the International System of Units. A mole of a substance or a mole of particles is defined as exactly particles, which can be atoms, molecules, ions, or electrons is the Avogadro number.

Complete answer:
The formula for number of moles is given by
$n = \dfrac{m}{M}$
where,
$n$ is the number of moles,
$m$ is the mass of a substance,
$M$ is molar mass (which is equivalent to atomic weight on the periodic table).
We know the molar mass of sodium is $= 23g$
Given $0.7\;$ moles of $Na$
Hence ,on substituting the values in the above formula, we get
$0.7 = \dfrac{m}{{23}}$
$\Rightarrow m = 23 \times 0.7$
Therefore the weight of the substance is
$m = 16.1$
Hence, we can say that $16.1g$ of sodium is present in $0.7$ moles of $Na$
Therefore, option (A) is the correct option.

Note:
- In chemistry, the formula weight could be a quantity computed by multiplying the mass (in the atomic mass units) of every element during a formula by the amount of atoms of that element present within the formula, then adding all of the products together.
- Formula weights are especially useful in determining the relative weights of reagents and products in every reaction. These relative weights computed from the chemical equation are sometimes called as equation weights.