Question detail

Chemical changes case 135 reactivity-evidence. A student uses the reactivity series to justify an observation. Which option is best? Focus on that decreasing one unit means the hydrogen ion in Strong and weak acids (HT only), not on a neighbouring Unit 4.4 reaction idea.

Try the question, check the answer, then read the explanation to understand the curriculum point.

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At a glance

MCQ

Type

practice

Style

Topic

Reactions of acids

Question

A. Chemical changes case 135 reactivity-evidence: Uses the relative reactivity order to predict the change for that decreasing one unit means the hydrogen ion
B. Chemical changes case 135 reactivity-evidence: Chooses the product by memorising a colour instead of the series (Strong and weak acids (HT only))
C. Chemical changes case 135 reactivity-evidence: Says any metal can displace any other metal ion (that decreasing one unit means the hydrogen ion)
D. Chemical changes case 135 reactivity-evidence: Ignores whether the reacting substance is more or less reactive (Reactions of acids)

Answer

The correct option is Chemical changes case 135 reactivity-evidence: Uses the relative reactivity order to predict the change for that decreasing one unit means the hydrogen ion.

Explanation

The correct option is Chemical changes case 135 reactivity-evidence: Uses the relative reactivity order to predict the change for that decreasing one unit means the hydrogen ion. It is correct because it directly supports the approved learning objective to (HT only) Explain that decreasing pH by one unit means the hydrogen ion concentration increases by a factor of ten in Strong and weak acids (HT only). The other options are incorrect because they blur a Unit 4.4 concept boundary: acid versus alkali versus base, oxidation versus reduction, displacement versus reduction, electrolysis versus electroplating, anode versus cathode, positive versus negative ions, oxidation state versus ionic charge, or strong acid versus concentrated acid.

Common mistake

Misunderstanding pH Changes

Students often think that a decrease in pH by one unit results in a linear increase in hydrogen ion concentration, rather than an exponential increase.

Emphasize that a decrease in pH by one unit means the hydrogen ion concentration actually increases by a factor of ten, highlighting the logarithmic nature of the pH scale.

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Chemical changes case 134 redox-boundary. A student explains a redox change. Which option uses the safest chemistry wording? Focus on that decreasing one unit means the hydrogen ion in Strong and weak acids (HT only), not on a neighbouring Unit 4.4 reaction idea.