Question detail
If 10 g of magnesium oxide (MgO) is produced from the reaction of magnesium with oxygen, calculate the number of moles of magnesium oxide formed.
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
Question
Type
exam_style
Style
Topic
Use of amount of substance in relation to masses of pure substances
Question
If 10 g of magnesium oxide (MgO) is produced from the reaction of magnesium with oxygen, calculate the number of moles of magnesium oxide formed.
Answer
The amount of substance is measured in moles, written mol. In calculations, moles allow chemists to compare reacting amounts using balanced equations rather than comparing masses alone.
Explanation
The key point is that mol is the unit for chemical amount. This matters because reacting masses must often be converted into moles before they can be compared using equation coefficients. In exam marking, the important steps are to identify the correct relationship, substitute or interpret the values carefully, keep units consistent, and avoid mixing this calculation with neighbouring Unit 4.3 methods.
Common mistake
Confusing moles with mass
Students often confuse the concept of moles with mass, thinking that mass is the same as the amount of substance.
Remember that moles measure the amount of substance, while mass is measured in grams. Use the relationship between mass and moles to clarify this distinction.
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