The properties of oxides
3 marks · NormalWhen 4.8 g of magnesium is completely burned in excess oxygen, magnesium oxide (MgO) is formed. Magnesium oxide is then added to water, and only a small amount dissolves to form an alkaline solution.
Use the equation below and the information given to answer the following questions.
(Relative atomic masses: Mg = 24, O = 16)
Calculate the maximum mass of magnesium oxide (MgO) produced when all of the 4.8 g of magnesium reacts. Show your working.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
8.0 g (±0.1)
Also accept: 8 g
Common mistakes: Incorrect relative atomic masses; Incorrect mole ratio; Using 1:1 instead of 2:2 ratio
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Calculates moles of Mg using the formula moles = mass / Mr.
M2 (a) · 1 mark · Uses correct molar ratio from the equation to determine moles of MgO formed. (follow-through)
A1 (a) · 1 mark · Calculates the correct mass of MgO produced (8.0 g). (follow-through)
Worked solution
1. Calculate the number of moles of magnesium:
2. From the balanced equation, 2 moles of Mg produce 2 moles of MgO, so the number of moles of MgO produced is also 0.20.
3. Find the formula mass of MgO: 24 (Mg) + 16 (O) = 40.