2.4.6Inorganic Chemistry
Practical- Investigate Metals Reacting with Acids — Edexcel International GCSE Science Double Award 4SD0 - Chemistry Revision Notes & Topical Questions
5 min read 5 parts Lesson 18 of 52
Curriculum Equation Key pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: pH + pOH = 14
Part 1 of 5Method
1
Put on safety glasses, then add about 5 cm³ of dilute hydrochloric acid to each of three test tubes.
2
Add a similar length of magnesium ribbon to the first tube, a similar mass of iron filings to the second, and a similar mass of zinc turnings to the third.
3
Observe each tube, noting the rate of bubbling, any temperature change and whether the metal dissolves.
4
Test the gas produced with a lighted splint, where hydrogen gives a squeaky pop.
5
Repeat the experiment with dilute sulfuric acid, keeping the acid volume and concentration the same.
Part 2 of 5Observations
Ranking
- Magnesium is the most reactive of the three metals, zinc is next, and iron is the least reactive.
Similar products
- All three metals give a salt and hydrogen with both acids, so the reaction type is the same in each case.
Gas test
- The squeaky pop with a lighted splint confirms that the gas produced is hydrogen.
Acid choice
- Hydrochloric and sulfuric acids give similar results, so the metal, not the acid, controls the rate of reaction.
| Metal | Dilute hydrochloric acid | Dilute sulfuric acid |
|---|---|---|
| Magnesium | Vigorous bubbling, gets hot and dissolves quickly | Vigorous bubbling and dissolves quickly |
| Zinc | Steady bubbling; metal dissolves slowly | Steady bubbling; metal dissolves slowly |
| Iron | Slow bubbling with small bubbles | Slow bubbling with small bubbles |
Part 3 of 5Equations
Equations
Magnesium and HCl
- Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g), showing magnesium forming magnesium chloride solution.
Zinc and H₂SO₄
- Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g), forming zinc sulfate and hydrogen gas.
Iron and HCl
- Fe(s) + 2HCl(aq) → FeCl₂(aq) + H₂(g), giving a pale green iron(II) chloride solution.
Fair test
- Keep the temperature, acid volume and metal size the same so that the results can be compared fairly.
Part 4 of 5Worked Example
Question Identify the independent, dependent and control variables in this investigation.
- The independent variable is the type of metal, which the student deliberately changes.
- The dependent variable is the rate of bubbling or the time taken for the metal to disappear, which is measured.
- The control variables are the acid type and volume, the concentration of the acid, the mass or size of the metal, and the temperature.
- Keeping the control variables constant means that only the metal affects the result, so the test is fair.
Answer
- Independent: metal type.
- Dependent: rate of reaction.
- Controlled: acid, volume, concentration, metal size and temperature.
Part 5 of 5Exam Checklist & Tips
2.4.6 – Key Points for the Exam
- Independent variable The factor that is deliberately changed by the investigator.
- Dependent variable The factor that is measured as the result of changing the independent variable.
- Control variable A factor that is kept the same so that the test is fair.
- Fair test An investigation in which only one variable is changed.
- Salt An ionic compound formed when a metal reacts with an acid, replacing the hydrogen.
Common Mistakes
- Using different masses or sizes of metal, which makes the comparison of reaction rates unfair.
- Saying magnesium reacts with hydrochloric acid to give water; the products are a salt and hydrogen.
- Claiming hydrogen is present without first testing the gas with a lighted splint.
- Recording iron as the most vigorous reaction; iron is the least reactive of the three metals.
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