Question detail
A sample of magnesium oxide (MgO) has a mass of 40 g. Calculate the percentage by mass of magnesium in magnesium oxide.
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
Question
Type
exam_style
Style
Topic
Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations
Question
A sample of magnesium oxide (MgO) has a mass of 40 g. Calculate the percentage by mass of magnesium in magnesium oxide.
Answer
60.3%
Explanation
This answer is strong as it demonstrates the calculation of the percentage by mass of magnesium in magnesium oxide, showing understanding of the relationship between mass and composition. The question tests the student's ability to apply the concept of percentage composition in a practical context.
Common mistake
Confusing Masses
Students often confuse relative formula mass (Mr) with relative atomic mass (Ar), leading to incorrect calculations in quantitative chemistry.
To fix this, remember that relative formula mass is the sum of the relative atomic masses of all atoms in a formula, while relative atomic mass refers to a single atom. Always check if you are calculating for a compound (Mr) or an element (Ar). Keep the correction anchored to Relative formula mass; check formula, substitution, calculation, final answer, and unit where relevant.
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