Question

If the atomic mass of sodium (Na) is 23, the number of moles in 46gm of sodium is:
A) 1
B) 2
C) 2.3
D) 4.6

Answer 1

Hint: A mole is about $6.022\times {{10}^{23}}$ particles.
The particles can be atoms, molecules or ions. Diving the given mass with the molecular mass will give us the number of moles.

Complete step by step solution:
In the question we are provided with the atomic mass of Na, which is 23g. We are supposed to find out the number of moles of sodium that makes 46gm.
We should know some of the basic ideas, what one mole is and how the atomic mass is related to finding the number of moles of an element.
We are always concerned about the particles in the atomic level, so we need a convenient way of expressing the number of particles in an atom. Clearly speaking just imagine 1g of Na, it contains a large number of particles which is hard for us to express, so to express it conveniently, the mole concept was introduced.
A mole is that amount of substance which contains exactly $6.022\times {{10}^{23}}$ elementary particles. We can express the number of particles of the given substance in a much simpler way, in terms of moles.
The value $6.022\times {{10}^{23}}$ is usually termed as Avogadro number, ${{N}_{A}}$
An equation for mole was coined as $n=\dfrac{N}{{{N}_{A}}}$,
Where n is the number of moles
N=Total number of elementary particles and ${{N}_{A}}$ is the Avogadro number
Given data:
Atomic mass or molecular mass of the sodium =23g
Given weight of sodium= 46g
Number of moles of sodium = given weight of sodium/ molecular mass of the sodium
Number of moles of sodium = $\dfrac{46}{23}=2$

So here the number of moles of sodium of 46g sodium is 2 moles, the correct option is option (B).

Note: If in the question, atomic mass is not given and atomic number is given, then atomic mass is the summation of number of electrons or protons and number of neutrons present in the atom. The number of moles for molecule may not be same number of moles of the constituent atoms .For example for one mole of water molecule there are 2 moles of hydrogen and one mole of oxygen