Chemistry - C3- Mole and Stoichometry

What is a mole?

1 mol = 6.02 × 10²³ particles. It is a unit that counts particles.

What things can a mole count?

Atoms, ions, and molecules.

Why do chemists use moles?

Because particles are too small to count one by one.

What is Avagadro’s constant?

6.02 × 10²³ , the number of particles in one mole.

What is molar mass?

The mass of 1 mole of a substance

How do you calculate molar mass?

Add the atomic mass of all the atoms in the formula.

(e.g. H₂O = 2×1+16=18 g/mol)

How to find moles from a known mass?

moles (mol) = mass(g) / molar mass (g/mol)

How do you find mass if you know moles?

mass(g) = moles x molar mass

What does a balanced equation show?

The ratio of moles of reactants and products.

What is the limiting reactant?

The reactant that runs out first and stops the reaction.

What is the excess reactant?

The reactant that is left over after the reaction.

What is stoichiometry?

Using a balanced equation to calculate amounts.

How do you calculate the mass of a substance in a reaction?

• Write the balanced equation.

• Find moles of the substance you are given:
  moles=massmolar mass\text{moles} = \frac{\text{mass}}{\text{molar mass}}moles=molar massmass​.

• Use the mole ratio from the equation.

• Find moles of the substance you need.

• Convert moles back to mass:
  mass=moles×molar mass\text{mass} = \text{moles} \times \text{molar mass}mass=moles×molar mass.

One mole of atoms or molecules…

is equal to the mass of that substance.

Calculate the number of moles in 90 g of water.
Mr(H₂O) = 18.0

1. Write the formula: n=mMn = \dfrac{m}{M}n=Mm​

2. Substitute numbers: n=9018.0n = \dfrac{90}{18.0}n=18.090​

3. Calculate: n=5.0n = 5.0n=5.0

A: 5.0 mol of H₂O

Calculate the mass of 0.200 mol of KBr.
Mr(KBr) = 119.0

1. Write the formula: m=n×Mm = n \times Mm=n×M

2. Substitute numbers: m=0.200×119.0m = 0.200 \times 119.0m=0.200×119.0

3. Calculate: m=23.8m = 23.8m=23.8

A: 23.8 g of KBr

0.500 mol of substance X has a mass of 87.0 g. Find Mr(X).

1. Rearrange: M=mnM = \dfrac{m}{n}M=nm​

2. Substitute numbers: M=87.00.500M = \dfrac{87.0}{0.500}M=0.50087.0​

3. Calculate: M=174M = 174M=174

A: Relative formula mass of X = 174