The Mole Flashcards

All 9 cards in this deck

How is one mole of particles of a substance defined in terms of number of particles?

The Avogadro constant number of particles, $6.02 \times 10^{23}$ atoms, molecules, formulae or ions.

How is one mole of a substance defined in terms of mass?

A mass in grams equal to the relative particle mass ($A_r$ or $M_r$) of that substance.

What is the value of the Avogadro constant?

$6.02 \times 10^{23}$ per mole.

What is the formula linking moles, mass and relative formula mass?

moles $= \dfrac{\text{mass (g)}}{M_r}$

How do you calculate the number of moles in a given mass of a substance?

e.g. 0.1 g of magnesium ($A_r$ = 24)

Divide the mass by the relative particle mass.
$0.1 \div 24 = 4.2 \times 10^{-3}$ mol

True or false? One mole of water molecules and one mole of carbon atoms contain the same number of particles.

True. One mole of any substance contains $6.02 \times 10^{23}$ particles, though their masses differ.

How do you calculate the number of particles in a given number of moles?

e.g. 3.5 mol of $\mathrm{O_2}$ molecules

Multiply moles by the Avogadro constant.
$3.5 \times 6.02 \times 10^{23} = 2.107 \times 10^{24}$ molecules

What are the steps to calculate the number of particles in a given mass of a substance?

e.g. molecules in 36 g of water ($M_r$ = 18)

1. Moles $=$ mass $\div M_r$: $36 \div 18 = 2$
2. Particles $=$ moles $\times 6.02 \times 10^{23}$: $1.204 \times 10^{24}$ molecules

How do you find the number of atoms in a given number of moles of a compound?

e.g. 2 mol of $\mathrm{H_2O}$

Multiply moles by $6.02 \times 10^{23}$, then by the number of atoms in one formula unit (3 for $\mathrm{H_2O}$).
$2 \times 6.02 \times 10^{23} \times 3 = 3.61 \times 10^{24}$ atoms