Describes a reaction using a symbol equation with coefficients, which ensure there are equal numbers of atoms of each element on both sides of the symbol equation.

Refers to the molar ratio of the reactants and products in a chemical reaction.

A mole of something is 6.02 × 10²³ of it. The mass of a mole of a substance is its relative mass expressed in grams.

Ratio can be used to determine the size of one quantity in relation to another.

Determining an equation from given values

Combined science

In the Making salts unit, pupils will learn about the production of pure salts, concentration and strength of acids, and what makes acids acidic and how bases can neutralise them.

In the Understanding Chemical Reactions unit, pupils learned about how atoms rearrange during chemical reactions and the conservation of mass.

Calculations involving masses

The formula for sulfuric acid is H₂SO₄. What is the ratio of oxygen to sulfur in the formula?

2Ca(OH)₂ + 4HNO₃ → 2Ca(NO₃)₂ + 4H₂O

2Ca(OH)₂ + 2HNO₃ → 2Ca(NO₃)₂ + 2H₂O

Ca(OH)₂ + 4HNO₃ → Ca(NO₃)₂ + 4H₂O

4Ca(OH)₂ + 2HNO₃ → 4Ca(NO₃)₂ + 2H₂O

Which of the following chemical equations shows a similar molar ratio to the reaction?: 
Ca(OH)₂ + 2HNO₃ → Ca(NO₃)₂ + 2H₂O

6 moles of calcium hydroxide, Ca(OH)₂, react with excess nitric acid, HNO₃. How many moles of water are formed in the reaction?
Ca(OH)₂ + 2HNO₃ → Ca(NO₃)₂ + 2H₂O

0.5 g of magnesium reacts with oxygen to form 0.8 g of magnesium oxide. Calculate the number of moles of magnesium oxide formed during the reaction. Relative atomic masses: Mg = 24; O = 16. 

What is the reacting ratio when 12.0 g of magnesium, Mg, reacts with 8.0 g of oxygen, O₂, to produce magnesium oxide? 

Write down the chemical formula for each reactant and product.

Calculate the relative formula mass for each substance.

Calculate the number of moles for each substance.

Find the unitary ratio (one ratio value should be 1).

Find the molar ratio (these should be whole numbers).

Convert the molar ratio to a balanced symbol equation.

It is possible to determine the balanced symbol equation of a reaction from the molar ratios using the following step. Place the steps into the correct order. 

The ratio of black pens to green pens is 1 : 3

The ratio of red pens to green pens is 2 : 1

The ratio of green pens to black pens is 1 : 3

The ratio of red pens to black pens is 3 : 2

A beaker contains six pens. Three pens are black, two are red and one is green. Which of the follow ratios are correct? 

Which empirical formula shows a metal to non-metal ratio of 1 : 2?

True or false? The unit for relative atomic mass is grams.

When a chemical is __________ there will always be some left over at the end of the reaction.

Calculate the relative formula mass of ammonium nitrate, NH₄NO₃. Relative atomic masses: N = 14; H = 1; O = 16. 

Starter Quiz