What is the mass of one mole of neon (Ne)? How many moles are there in 5 g of neon gas? How many atoms are there in this quantity of neon? What volume does this quantity of neon gas occupy at s.t.p.? - Leaving Cert Chemistry - Question c - 2015

To calculate the number of moles in 5 g of neon gas, we use the formula:

$ext{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$

Substituting the values:

$\text{Number of moles} = \frac{5}{20} = 0.25 \text{ moles}$

To find the number of atoms in 0.25 moles of neon, we use Avogadro's number, which is approximately $6.022 \times 10^{23}$ atoms/mol:

$\text{Number of atoms} = \text{moles} \times \text{Avogadro's number}$

$\text{Number of atoms} = 0.25 \times 6.022 \times 10^{23} \approx 1.5 \times 10^{23} \text{ atoms}$

At standard temperature and pressure (s.t.p.), one mole of gas occupies 22.4 liters. Therefore, for 0.25 moles:

$\text{Volume} = 0.25 \times 22.4 = 5.6 \text{ liters}$

In cubic centimeters, this is equivalent to:

$5.6 \text{ liters} = 5.6 \times 1000 = 5600 \text{ cm}^3$