A cleaning solution is used to remove limescale, CaCO3, from bathroom surfaces. When the solution is sprayed onto the limescale, effervescence (fizzing) occurs and the solid limescale begins to disappear. This chemical reaction is needed because the limescale cannot be removed with water alone. Which of the following statements about this chemical reaction are correct? 1 The cleaning solution is acidic. 2 The effervescence (fizzing) is caused by the release of hydrogen gas. 3 The pH of the reacting solution will go down as the reaction proceeds. 4 The salt produced in the reaction is more soluble than CaCO3
Correct answer: B. 1 and 4 only
- A. 1 and 3 only
- B. 1 and 4 only
- C. 2 and 3 only
- D. 1, 3 and 4
Explanation
The correct answer is C, which means that only statements 1 and 4 are correct.Statement 1 is correct because limescale is composed of calcium carbonate (CaCO3), which is a base, and an acid-based cleaning solution is needed to react with it. The acid in the cleaning solution can neutralize the base and break down the limescale.Statement 2 is incorrect because the effervescence is caused by the release of carbon dioxide gas, not hydrogen gas. When an acid reacts with a carbonate, carbon dioxide gas is produced as a byproduct, which is what causes the effervescence.Statement 3 is incorrect because the pH of the reacting solution will not actually decrease as the reaction proceeds.Statement 4 is correct because the salt produced in the reaction, calcium acetate (Ca(CH3COO)2), is more soluble than CaCO3. This means that it can dissolve in water more easily, allowing it to be rinsed away along with the limescale.Therefore, the correct answer is C, which includes only statements 1 and 4 as correct.
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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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