C3 - Quantitaive Chemistry

What is the law of conservation of mass?

No atoms are created or destroyed during a chemical reaction, so the total mass stays the same

Why does the mass of products equal the mass of reactants?

The number and the type of atoms do not change

What should happen to total mass in a closed system?

It stays the same before and after the reaction

Why might the mass appear to change in a reaction?

If a gas is involved, it can enter or leave the reaction vessel

Give an example of a reaction where mass appears to increase

When a metal reacts with oxygen to form an oxide

Give an example of a reaction where the mass appears to decrease

When a metal carbonate decomposes to form a gas that escapes

Calcium carbonate →  Calcium oxide + Carbon dioxide

How is relative formula mass (Mr) calculated?

By adding the relative atomic masses (Ar) of all the atoms in the formula

What is the Mr of H₂O?

(2×1) + 16 = 18

How do you calculate the percentage mass of an element in a compound?

(Ar x number of atoms of that element) ÷ (Mr of the compound) X 100

What is Avogadro’s constant?

6.02 × 10²³ particles per mole

What is a mole?

An amount of that substance that contains an Avogadro number of particles – so 6.02 × 10²³ particles

What is one mole?

The amount of substance that contains the same number of particles as atoms in 12 g of carbon-12

What is the equation you would use to calculate the mole?

Mole = Mass ÷ Mr

How would you calculate the mass?

Mass = Moles x Mr

How would you calculate the Mr?

Mr = Mass ÷ moles

What do the big numbers in an equation represent?

The number of moles of each substance

What is concentration?

The amount of a substance in a certain volume of a solution

The more solute there is in a given volume, the more concentrated it is

How do you calculate the concentration of a solution?

Concentration = Mass ÷ Volume

Concentration = Mol ÷ volume

What are the units for concentration?

g/dm³

What is a limiting reactant?

The reactant that is completely used up first, stopping the reaction

What happens to the other reactant(s)?

They are in excess

What is atom economy?

How efficiently atoms in reactants are used to make the desired product

What is the formula for atom economy?

(Mr of product ÷ total Mr of all products) x 100

Why is atom economy important?

To reduce waste, save  raw materials, and protect the environment

What is percentage yield?

How much product is made compared to the maximum possible

What is the equation for percentage yield?

(Actual yield ÷ theoretical yield) × 100