Chemistry - QUANTITATIVE CHEMISTRY (C3)

Relative Formula Mass (Mr) -

What is the relative formula mass (Mr)?

The sum of the relative atomic masses (Ar) of all the atoms in a formula.

Relative Formula Mass (Mr) -

How do you calculate the Mr of H2O?

H: 1×2 = 2

O: 16

Mr = 2 + 16 = 18

The Mole & Avogadro’s Constant -

What is one mole of a substance?

The amount of a substance that contains 6.02 × 10²³ particles (atoms, molecules, ions, etc).

The Mole & Avogadro’s Constant -

What is Avogadro’s constant?

6.02 × 10²³ mol⁻¹, the number of particles in one mole.

The Mole & Avogadro’s Constant -

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

Moles = Mass (g) / Mr

The Mole & Avogadro’s Constant -

How do you calculate mass from moles?

Mass = Moles x Mr

Chemical Equations & Moles -

Why must chemical equations be balanced?

To show the conservation of mass - atoms are neither created nor destroyed.

Chemical Equations & Moles -

How do you use moles to balance equations?

Calculate the moles of each substance + use them to determine the ratio of reactants + products.

Limiting Reactants -

What is a limiting reactant?

The reactant that’s completely used up first + limits the amount of product formed.

Limiting Reactants -

Why is the limiting reactant important in chemical reactions?

It determines the maximum amount of product that can be formed.

Concentration of Solutions -

How is concentration calculated?

Concentration = Mass of solute (g) / Volume of solution (dm³)

Concentration of Solutions -

What unit is concentration usually given in?

Grams per decimetre cubed (g/dm³).

Concentration of Solutions -

How do you convert cm³ to dm³?

Divide by 1000 (1 dm³ = 1000 cm³).

Conservation of Mass & Gas loss -

Why might mass appear to decrease in a reaction?

If a gas is produced + escapes from an unsealed container.

Conservation of Mass & Gas loss -

Why might mass appear to increase?

If a gas from the air is added during the reaction.

Percentage Yield & Atom Economy -

What is the formula for percentage yield?

(Actual yield / Theoretical yield) x 100

Percentage Yield & Atom Economy -

What is atom economy?

(Mr of desired product / Sum of Mr of all reactants) x 100