Experiment: Dilute hydrochloric acid was added to marble chips in a conical flask connected to a gas syringe.Observation: Gas volume increased with time until it plateaued.Question: What can be concluded?
Correct answer: C. Reaction rate decreases as reactants are used up.
- A. Marble turns into gas over time
- B. Gas leaks caused the stop in reaction.
- C. Reaction rate decreases as reactants are used up.
- D. Acid stopped boiling due to temperature drop.
Explanation
The correct answer is C, because as the chemical reaction proceeds, the particles of the reactants (marble chips and acid) are used up to form the products.Initial Stage: There are a large number of particles of the reactants, and hence the collision frequency is high, and the gas evolves readily.Middle Phase: The concentration of the acid and the surface area of the marble are decreasing because the reactants are being consumed. This causes the collisions to slow down, leading to a decrease in the rate of reaction.The Plateau: The volume of gas evolved ceases to rise (plateaus) because a gas has reacted completely, meaning that this particular chemical reaction is complete.
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About Scientific Reasoning
Scientific reasoning evaluates hypotheses through observations, variables, controls, measurements and experimental results. Questions involve identifying independent and dependent variables, recognising a fair test, interpreting tables or graphs, distinguishing evidence from opinion, and deciding whether data supports, rejects or leaves a hypothesis unresolved.
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