1. Calculations using balanced chemical equations Revision
National 5 Chemistry
Calculations using balanced chemical equations
Revision

2. Calculate the mass of magnesium oxide formed when 6g of magnesium is burned in air.
2 Mg O MgO
Step 1: write down the balanced chemical equation if it is not given

3. Calculate the mass of magnesium oxide formed when 6g of magnesium is burned in air.
2 Mg O MgO
Step 2: select the substance being asked about and the substance you have been given information about

4. Calculate the mass of magnesium oxide formed when 6g of magnesium is burned in air.
2 Mg O MgO
2 mol
1 mol
1 mol
Step 3: write down the number of moles of each and simplify if possible

5. Calculate the mass of magnesium oxide formed when 6g of magnesium is burned in air.
2 Mg O MgO
1 mol
1 mol
24.5 g
( ) g
40.5 g
Step 3: change moles to grams (data book page 7)

6. Calculate the mass of magnesium oxide formed when 6g of magnesium is burned in air.
2 Mg O MgO
24.5 g
40.5 g
6 g y
Step 4: put in what you are trying to find (call it x or y)

7. Calculate the mass of magnesium oxide formed when 6g of magnesium is burned in air.
2 Mg O MgO
24.5 g
40.5 g
6 g y
x y =
6 x 40.5 =
6 x 40.5
24.5 y
= g
Step 5: cross multiply and solve to get the answer