Reactions of metals with dilute acids
3 marks · NormalExplain why it is important to use the same number of moles of metal in each experiment when comparing their reactivity with dilute hydrochloric acid.
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Also accept: Because more moles (particles) would produce more heat and gas, making comparison unfair; same moles ensures observed changes are due to reactivity, not quantity.
Common mistakes: Saying only 'to be fair' with no explanation.; Focusing on mass instead of moles.
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Marking points
B1 · 1 mark · Mentions that different numbers of moles mean different amounts of reaction (gas, heat).
B2 · 1 mark · States that using the same moles makes the comparison fair/valid.
B3 · 1 mark · Explains that using same mass can give different moles for each metal, making results not comparable.
Worked solution
If we use different numbers of moles of metals, some tests would produce more heat or gas simply because there are more particles/reactants, not because the metal is more reactive.
Using the same amount (in moles) of each metal gives a fair test, so we can compare their reactivity based on the same quantity of substance.
Since metals have different molar masses, using the same mass would result in different numbers of moles, making the comparison unfair.