Why is "Writing 'metal + acid → salt' and forgetting the hydrogen" a common mistake in Investigating metals reaction to acids?

Why it happens: Students focus on naming the salt and forget the gas is a product too. How to avoid it: Always write **salt + hydrogen** — the reaction with a reactive metal always gives off hydrogen gas. Source: Edexcel Chemistry examiner reports — recurring error

Why is "Saying a glowing splint relights for the hydrogen test" a common mistake in Investigating metals reaction to acids?

Why it happens: Students mix up the hydrogen test with the test for oxygen. How to avoid it: Hydrogen = **lighted splint → squeaky pop**. A glowing splint relighting is the test for **oxygen**, not hydrogen. Source: Edexcel Chemistry examiner reports

Why is "Forgetting surface area as a control variable" a common mistake in Investigating metals reaction to acids?

Why it happens: Students remember to keep the acid and mass the same but overlook the size/shape of the metal pieces. How to avoid it: List **same surface area (same size pieces)** as a control — powder reacts faster than a lump of the same mass, so it would make the test unfair. Source: Edexcel Chemistry examiner reports

Why is "Writing 'use the same amount of acid' instead of volume AND concentration" a common mistake in Investigating metals reaction to acids?

Why it happens: 'Amount' feels complete but is not specific enough for the mark. How to avoid it: Specify **same volume of acid AND same concentration of acid** — both must be controlled. Source: Edexcel Chemistry examiner reports

Why is "Saying copper 'is just unreactive' without explaining why it gives no gas" a common mistake in Investigating metals reaction to acids?

Why it happens: Students know copper does not react but cannot justify it. How to avoid it: State that copper is **below hydrogen in the reactivity series**, so it cannot displace hydrogen from the acid — therefore no reaction. Source: Edexcel Chemistry examiner reports

Why is "Calculating average rate without converting minutes to seconds (or omitting the unit)" a common mistake in Investigating metals reaction to acids?

Why it happens: Times given as '1 min 10 s' are mis-read as 1.10, and units are forgotten. How to avoid it: Convert to seconds first (1 min 10 s = 70 s), then use rate = volume ÷ time, and always write the unit **cm³/s**. Source: Edexcel Chemistry examiner reports

Reactivity seriesEdexcel IGCSE Science(Double Award)-Chemistry (4WSD0-1C)

Investigating metals reaction to acids

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Investigating Metals' Reaction to Acids — Edexcel International GCSE Science (Double Award) Chemistry (4WSD0-1C) Study Notes

The required practical that ranks metals by reactivity from their reaction with dilute acid: metal + acid → salt + hydrogen. How to make it a fair test, how to measure the rate (gas volume, temperature rise or time to disappear), and how to read the results to put metals in order. Covers Double Award Chemistry spec 2.15, assessed on Chemistry Paper 1 (4WSD0/1C).

What you’ll learn

Mapped to the Edexcel IGCSE 4WSD0-1C syllabus (2026 onwards).

2.15 — Investigate and compare the reactivity of metals using their reactions with dilute acid (salt + hydrogen).

The reaction: metal + acid → salt + hydrogen (spec 2.15)

Reactive metals react with dilute acid to give a salt and hydrogen gas — the more reactive the metal, the faster it fizzes.

When a reactive metal is added to a dilute acid, it fizzes and a gas is given off. The general word equation you must know is:

metal + dilute acid → salt + hydrogen

The salt formed depends on the acid: hydrochloric acid (HCl) makes a chloride; sulfuric acid (H₂SO₄) makes a sulfate.

Worked example with magnesium and hydrochloric acid:

$\text{Mg(s)} + 2\text{HCl(aq)} \rightarrow \text{MgCl}_2\text{(aq)} + \text{H}_2\text{(g)}$

The key idea for this practical: the more reactive the metal, the faster and more vigorous the reaction. So if we let several metals react with the same acid and watch how fast they fizz, we can put them in order of reactivity.

Sign of a faster (more reactive) reaction	What you see / measure
More vigorous fizzing	More/bigger bubbles, faster
More gas given off per second	Gas syringe fills faster
Bigger temperature rise	Thermometer reads higher (exothermic)
Metal disappears sooner	Shorter time to dissolve

Which metals react? Only metals above hydrogen in the reactivity series react with dilute acid. Magnesium, zinc and iron react; copper does not react because it is below hydrogen — no fizzing, no gas, no temperature rise.

Metal + dilute acid → salt + hydrogen.
HCl → chloride salt; H₂SO₄ → sulfate salt.
More reactive = faster, more vigorous, more gas, bigger temperature rise.
Only metals above hydrogen react; copper does not react with dilute acid.

See the full worked example for investigating metals reaction to acids →

Testing for the gas — the squeaky pop (spec 2.15)

The gas given off is hydrogen — confirmed by a lighted splint giving a squeaky pop.

The bubbles given off in this reaction are hydrogen. You must know the exact test and the exact result — it is a high-value identification mark.

Test for hydrogen: hold a lighted (burning) splint at the mouth of the test tube.

Result: the gas burns with a squeaky pop.

Get the wording right: the answer is "lighted splint → squeaky pop". Writing "it pops" or "a glowing splint relights" loses the mark (a glowing splint relighting is the test for oxygen, not hydrogen).

Hydrogen is collected in a gas syringe so its volume can be read off against time.

The diagram above is also the apparatus used to measure the rate of the reaction, covered next.

The gas is hydrogen.
Test: lighted splint at the mouth of the tube.
Result: squeaky pop = hydrogen confirmed.
A glowing splint relighting is the test for oxygen — do not confuse them.

See the full worked example for investigating metals reaction to acids →

The method — measuring and ranking reactivity (spec 2.15)

Measure the rate (gas volume, temperature rise or time to disappear) for each metal, then rank from the results.

Aim: compare the reactivity of several metals (e.g. magnesium, zinc, iron and copper) using their reactions with dilute acid.

Three ways to measure how fast each metal reacts:

Volume of gas vs time — collect the hydrogen in a gas syringe (or upturned measuring cylinder) and record the volume every few seconds. The metal that produces gas fastest (steepest line on a graph) is most reactive.
Temperature rise — the reaction is exothermic, so measure the temperature increase with a thermometer. A bigger rise = more reactive.
Time for the metal to disappear — time how long the same mass of metal takes to dissolve completely. A shorter time = more reactive.

Fair test — control variables. To make it a fair comparison, only the type of metal should change. Keep everything else the same:

Keep the same (control variables)	Change (independent variable)	Measure (dependent variable)
Volume of acid	Type of metal	Volume of gas / temperature rise / time
Concentration of acid
Mass of metal
Surface area of metal (same size pieces)
Temperature at the start

Why surface area matters: powdered metal reacts faster than a single lump of the same mass, so all metals must have the same surface area (e.g. all small ribbons or all powder) — otherwise the comparison is unfair.

Typical result table:

Metal	Observation	Reactivity
Magnesium	Very vigorous fizzing; fast; large temperature rise	Most reactive
Zinc	Steady fizzing
Iron	Slow, gentle fizzing
Copper	No reaction at all	Least reactive

Conclusion (the order from these results): Mg > Zn > Fe > Cu.

Three measures of rate: gas volume vs time, temperature rise, time to disappear.
Steepest gas-volume line = most reactive; biggest temperature rise = most reactive.
Control: same volume + concentration of acid, same mass + surface area of metal.
Same surface area is essential — powder reacts faster than a lump.
Result order: Mg > Zn > Fe > Cu (Cu does not react).

See the full worked example for investigating metals reaction to acids →

Reading the results — graphs and rate (spec 2.15)

Steeper, higher curve = more reactive; average rate = total gas ÷ time.

Results are often plotted as volume of gas against time. You must be able to read these graphs.

A steeper line and a faster level-off both mean a more reactive metal. All three level off at the same final volume because the same mass of metal was used.

How to read it:

Steeper line at the start = faster reaction = more reactive metal. Magnesium is steepest, so it is the most reactive.
The line levels off when the reaction has finished (one reactant is used up). The steepest curve also flattens first.
All three reach the same final volume here because the same mass of metal was used — the metal type changes the speed, not the amount of gas.

Calculating average rate:

$\text{average rate} = \frac{\text{total volume of gas}}{\text{time taken}}$

For example, if 48 cm³ of hydrogen is collected in 60 s:

average rate = 48 ÷ 60 = 0.8 cm³/s.

A higher average rate means a faster, more reactive metal.

Steeper line = faster reaction = more reactive.
Line flattens when a reactant runs out; steepest curve flattens first.
Same mass of metal → same final gas volume.
Average rate = total gas volume ÷ time (cm³/s).

See the full worked example for investigating metals reaction to acids →

How it’s examined

Double Award Chemistry is assessed on one untiered paper — Chemistry Paper 1 (4WSD0/1C), 2 hours, 110 marks, 33.3% of the Double Award (calculator allowed). This required practical is examined as: write the word/balanced equation for metal + acid (1–2 marks); state the gas test and result (lighted splint → squeaky pop, 2 marks); identify control variables for a fair test (2–3 marks); interpret a volume-of-gas-vs-time graph to rank metals (3–4 marks); and calculate an average rate (2 marks). The biggest discriminators are giving the exact gas-test wording and naming the correct control variables (especially surface area).

Sources: Pearson Edexcel International GCSE Science (Double Award) 4SD0 specification — Issue 4 (valid for 2026 onwards); Pearson Edexcel International GCSE Chemistry 4CH1 specification — Issue 4 (shared Chemistry Paper 1 content); Pearson Edexcel 4SD0 / 4CH1 examiner reports 2022–2024. Last reviewed 2026-06-07.

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Step-by-step worked examples — Investigating metals reaction to acids

Step-by-step solutions to past-paper-style questions on investigating metals reaction to acids, written exactly the way a tutor would explain them at the board.

1Write the equation for metal + acid (Getting started)
Getting started• 4WSD0/1C style — short answer• equation, spec-2.15
Question
Magnesium reacts with dilute hydrochloric acid. (a) Write the word equation. (b) Name the gas given off. (3 marks)
Step-by-step solution
1. Step 1
  (a) Pattern (1). Every metal + acid reaction follows: metal + acid → salt + hydrogen.
2. Step 2
  (a) The salt (1). Hydrochloric acid gives a chloride, so the salt is magnesium chloride: magnesium + hydrochloric acid → magnesium chloride + hydrogen.
3. Step 3
  (b) The gas (1). The gas given off is hydrogen.
Answer
(a) magnesium + hydrochloric acid → magnesium chloride + hydrogen. (b) Hydrogen.
Examiner tip
The reliable pattern is 'salt + hydrogen'. With hydrochloric acid the salt is always a chloride; with sulfuric acid it is a sulfate. Forgetting the hydrogen (writing only the salt) is a common dropped mark.
2Test for the gas given off (Getting started)
Getting started• 4WSD0/1C style — short answer• gas-test, spec-2.15
Question
Describe how you would test the gas produced when zinc reacts with dilute acid, and give the result. (2 marks)
Step-by-step solution
1. Step 1
  Test (1). Hold a lighted (burning) splint at the mouth of the test tube.
2. Step 2
  Result (1). The gas burns with a squeaky pop — this shows the gas is hydrogen.
3. Step 3
  Watch out. A glowing splint relighting is the test for oxygen — do not write that here.
Answer
Hold a lighted splint at the mouth of the tube; the gas burns with a squeaky pop, confirming it is hydrogen.
Examiner tip
Both marks require the exact wording: 'lighted splint' and 'squeaky pop'. 'It pops' is usually accepted, but 'glowing splint relights' is the oxygen test and scores zero.
3Make it a fair test (Building confidence)
Building confidence• 4WSD0/1C style — structured• fair-test, variables, spec-2.15
Question
A student compares the reactivity of magnesium, zinc and iron by adding each metal to dilute acid and timing the reaction. Give three variables the student must keep the same to make this a fair test. (3 marks)
Step-by-step solution
1. Step 1
  Acid amount (1). Same volume of acid used each time.
2. Step 2
  Acid strength (1). Same concentration of acid each time.
3. Step 3
  The metal (1). Same mass and surface area of metal (same size pieces) each time — and the same starting temperature.
4. Step 4
  Reasoning. Only the type of metal should change; everything else is controlled so any difference is caused by the metal, not the conditions.
Answer
Same volume of acid; same concentration of acid; same mass and surface area of metal (same starting temperature). Only the type of metal changes.
Examiner tip
Surface area is the variable students most often forget — powdered metal reacts faster than a lump of the same mass, so it must be controlled. 'Same amount of acid' is too vague; specify volume AND concentration.
4Predict which metal fizzes fastest (Building confidence)
Building confidence• 4WSD0/1C style — structured• prediction, reactivity, spec-2.15
Question
Equal masses of magnesium, iron, zinc and copper are each added to separate test tubes of the same dilute hydrochloric acid. (a) Which metal fizzes fastest? (b) Which metal does not react at all, and why? (3 marks)
Step-by-step solution
1. Step 1
  (a) Fastest (1). The most reactive metal reacts fastest — of these, magnesium is the most reactive, so it fizzes fastest.
2. Step 2
  (b) No reaction (1). Copper does not react.
3. Step 3
  (b) Reason (1). Copper is below hydrogen in the reactivity series, so it is not reactive enough to displace hydrogen from the acid.
Answer
(a) Magnesium fizzes fastest (most reactive). (b) Copper does not react because it is below hydrogen in the reactivity series.
Examiner tip
Order of reactivity here: Mg > Zn > Fe > Cu. The 'below hydrogen' reason is essential for the copper mark — 'copper is unreactive' alone is too vague.
5Rank metals from a gas-volume graph (Stretch)
Stretch• 4WSD0/1C style — extended• graph, data, spec-2.15
Question
Three metals X, Y and Z were each reacted with the same dilute acid and the volume of gas was measured against time. On the graph, X gave the steepest line and levelled off first, Z gave the shallowest line, and Y was in between. (a) Place X, Y and Z in order of reactivity, most reactive first. (b) Explain how the graph shows this. (4 marks)
Step-by-step solution
1. Step 1
  (a) Order (1). Most reactive first: X > Y > Z.
2. Step 2
  (b) Steepness (1). A steeper line means gas is given off faster, so the reaction is faster.
3. Step 3
  (b) Link to reactivity (1). A faster reaction means a more reactive metal — X is steepest, so X is most reactive.
4. Step 4
  (b) Levelling off (1). X also levels off first, showing its reaction finishes soonest — further evidence it is the fastest/most reactive.
Answer
(a) X > Y > Z. (b) The steeper the line, the faster gas is produced and the more reactive the metal; X has the steepest line and levels off first, so it is most reactive, then Y, then Z.
Examiner tip
Marks are for linking 'steeper line → faster rate → more reactive'. Note all lines reach the same final volume if equal masses were used — only the steepness (rate) tells you the reactivity.
6Calculate the average rate of reaction (Stretch)
Stretch• 4WSD0/1C style — extended• calculation, rate, spec-2.15
Question
When magnesium reacts with dilute acid, 60 cm³ of hydrogen is collected in 40 s, after which no more gas is produced. (a) Calculate the average rate of reaction in cm³/s. (b) A second metal gives only 30 cm³ in the same 40 s. State whether it is more or less reactive than magnesium. (3 marks)
Step-by-step solution
1. Step 1
  (a) Formula (1). average rate = total volume of gas ÷ time taken.
2. Step 2
  (a) Substitute (1). average rate = 60 ÷ 40 = 1.5 cm³/s.
3. Step 3
  (b) Compare (1). The second metal produces gas more slowly (30 cm³ vs 60 cm³ in the same time), so it is less reactive than magnesium.
Answer
(a) 60 ÷ 40 = 1.5 cm³/s. (b) Less reactive than magnesium (slower rate of gas production).
Examiner tip
Always give the unit (cm³/s). For part (b), a slower rate of gas production = a less reactive metal. Students who quote a number without the unit lose the final mark.

Model Answers — Investigating metals reaction to acids

High-scoring sample answers for investigating metals reaction to acids on the Pearson Edexcel IGCSE Chemistry Paper 1 (4WSD0/1C) paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.

Question 1
4WSD0/1C style2 marks
Complete the general word equation: metal + dilute acid → ______ + ______. (2 marks)
Model answer
metal + dilute acid → salt + hydrogen

The salt (1) depends on the acid — a chloride from hydrochloric acid, a sulfate from sulfuric acid.

Hydrogen (1) gas is always given off.
Why this scores
1 mark for 'salt', 1 mark for 'hydrogen'. Leaving out hydrogen is the most common dropped mark on this question.
Question 2
4WSD0/1C style2 marks
State the test for hydrogen gas and the positive result. (2 marks)
Model answer
Test (1): hold a lighted (burning) splint at the mouth of the tube.

Result (1): the gas burns with a squeaky pop.
Why this scores
Both the test ('lighted splint') and the result ('squeaky pop') are needed. A glowing splint relighting is the oxygen test — a very common mix-up that scores zero.
Question 3
4WSD0/1C style4 marks
Zinc reacts with dilute sulfuric acid (H₂SO₄). (a) Name the salt formed. (b) Write the balanced symbol equation for the reaction. (4 marks)
Model answer
(a) The salt is zinc sulfate (sulfuric acid always gives a sulfate). (1)

(b) Balanced symbol equation:

$\text{Zn(s)} + \text{H}_2\text{SO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{H}_2\text{(g)}$

correct formulae of products ZnSO₄ and H₂ (1);

equation correctly balanced (1);

correct reactants Zn + H₂SO₄ shown (1).
Why this scores
ZnSO₄ + H₂SO₄ both contain the SO₄ group — make sure it is written correctly. State symbols are good practice but marks here are for formulae and balancing.
Question 4
4WSD0/1C style4 marks
Describe a method a student could use to compare the reactivity of zinc and iron using their reactions with dilute acid. Include one measurement they would take and two variables they must control. (4 marks)
Model answer
Add the same mass and surface area of zinc, then iron, to separate test tubes/flasks of acid. (1)

Use the same volume and concentration of acid for each metal. (1)

Measure the rate: collect the hydrogen in a gas syringe and record the volume of gas every few seconds (or measure the temperature rise, or time how long the metal takes to disappear). (1)

The metal producing gas fastest (steepest graph) / giving the biggest temperature rise / disappearing soonest is the more reactive. (1)
Why this scores
Mark scheme rewards: a valid measurement, named control variables, and a clear way to judge reactivity from the results. Vague answers ('see which fizzes more') without a measurement cap the marks.
Question 5
4WSD0/1C style — extended6 marks
Three metals A, B and C were each added to the same volume and concentration of dilute hydrochloric acid and the volume of hydrogen was recorded against time. The graph showed: A — steepest line, levels off first; B — less steep, levels off later; C — no gas produced at all. Use the graph to place A, B and C in order of reactivity and fully explain your reasoning, including why C behaves as it does. (6 marks)
Model answer
Order of reactivity (most reactive first): A > B > C. (1)

Why A is most reactive. A has the steepest line, so hydrogen is produced fastest — a faster reaction means a more reactive metal. A also levels off first, showing its reaction finishes soonest. (2)

Why B is in the middle. B's line is less steep, so gas is produced more slowly than for A — B reacts slower and is therefore less reactive than A but it still reacts, so it is more reactive than C. (1)

Why C produces no gas. C gives no hydrogen, so it does not react with the acid. This means C is below hydrogen in the reactivity series (e.g. copper) — it is not reactive enough to displace hydrogen from the acid. (2)
Why this scores
Top band needs: correct order, 'steeper line → faster rate → more reactive', AND a correct explanation that C is below hydrogen in the series. Many candidates rank A and B correctly but only say C is 'unreactive' without the 'below hydrogen' reason.
Question 6
4WSD0/1C style — extended6 marks
A student investigates the reactivity of three metals with dilute acid. (a) Explain why the metal pieces must have the same surface area for the test to be fair. (b) For one metal, 84 cm³ of hydrogen was collected in 1 minute 10 seconds. Calculate the average rate of reaction in cm³/s. (6 marks)
Model answer
(a) Surface area (up to 3 marks).

A larger surface area gives the acid more contact with the metal, so the reaction is faster. (1)

If the metals had different surface areas, the difference in rate could be caused by the surface area rather than by the type of metal. (1)

Keeping surface area the same means any difference in rate is due only to the metal's reactivity, making the comparison fair. (1)

(b) Average rate (up to 3 marks).

Convert the time: 1 min 10 s = 70 s. (1)

average rate = total gas volume ÷ time = 84 ÷ 70. (1)

average rate = 1.2 cm³/s. (1)
Why this scores
Part (b) catches students who forget to convert minutes to seconds (1 min 10 s = 70 s, not 1.10). Always show the unit cm³/s. Part (a) rewards linking surface area to a fair comparison of the metal itself.

Key Definitions and Keywords — Investigating metals reaction to acids

Definitions to memorise and the exact keywords mark schemes credit for investigating metals reaction to acids answers — sharpened from recent examiner reports for the 2026 Pearson Edexcel IGCSE Chemistry Paper 1 (4WSD0/1C) sitting.

Reactivity (of a metal)
Examiner keyword
How readily a metal reacts — a more reactive metal reacts faster and more vigorously with dilute acid, giving more gas per second and a bigger temperature rise.
Salt
Examiner keyword
The compound formed when a metal (or base) replaces the hydrogen of an acid — a chloride from hydrochloric acid, a sulfate from sulfuric acid.
Test for hydrogen
Examiner keyword
Hold a lighted splint at the mouth of the tube; the gas burns with a squeaky pop. This confirms the gas is hydrogen.
Fair test
Examiner keyword
An investigation in which only the independent variable (here, the type of metal) is changed while all other variables are kept the same.
Control variable
Examiner keyword
A variable kept the same throughout the experiment so it does not affect the result — e.g. volume and concentration of acid, mass and surface area of metal, starting temperature.
Independent variable
The one variable that is deliberately changed in the investigation — here, the type of metal.
Dependent variable
The variable that is measured to see the effect — here, the volume of gas, the temperature rise, or the time for the metal to disappear.
Surface area
Examiner keyword
The total exposed area of the metal. A larger surface area (e.g. powder) gives a faster reaction, so it must be kept the same for a fair comparison.
Average rate of reaction
The total volume of gas produced divided by the time taken (cm³/s); a higher average rate means a faster, more reactive metal.
Gas syringe
Apparatus used to collect and measure the volume of gas given off during a reaction, allowing the rate to be measured against time.

Common Mistakes and Misconceptions — Investigating metals reaction to acids

The traps other students keep falling into on investigating metals reaction to acids questions — taken from recent Pearson Edexcel IGCSE Chemistry Paper 1 (4WSD0/1C) examiner reports and mark schemes — and how to avoid them.

✕Writing 'metal + acid → salt' and forgetting the hydrogen
Edexcel Chemistry examiner reports — recurring error
Why it happens
Students focus on naming the salt and forget the gas is a product too.
How to avoid it
Always write salt + hydrogen — the reaction with a reactive metal always gives off hydrogen gas.
✕Saying a glowing splint relights for the hydrogen test
Edexcel Chemistry examiner reports
Why it happens
Students mix up the hydrogen test with the test for oxygen.
How to avoid it
Hydrogen = lighted splint → squeaky pop. A glowing splint relighting is the test for oxygen, not hydrogen.
✕Forgetting surface area as a control variable
Edexcel Chemistry examiner reports
Why it happens
Students remember to keep the acid and mass the same but overlook the size/shape of the metal pieces.
How to avoid it
List same surface area (same size pieces) as a control — powder reacts faster than a lump of the same mass, so it would make the test unfair.
✕Writing 'use the same amount of acid' instead of volume AND concentration
Edexcel Chemistry examiner reports
Why it happens
'Amount' feels complete but is not specific enough for the mark.
How to avoid it
Specify same volume of acid AND same concentration of acid — both must be controlled.
✕Saying copper 'is just unreactive' without explaining why it gives no gas
Edexcel Chemistry examiner reports
Why it happens
Students know copper does not react but cannot justify it.
How to avoid it
State that copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from the acid — therefore no reaction.
✕Calculating average rate without converting minutes to seconds (or omitting the unit)
Edexcel Chemistry examiner reports
Why it happens
Times given as '1 min 10 s' are mis-read as 1.10, and units are forgotten.
How to avoid it
Convert to seconds first (1 min 10 s = 70 s), then use rate = volume ÷ time, and always write the unit cm³/s.

Past paper style quiz

Get a report showing which sub-topics you've nailed and which ones still need work.

Investigating Metals' Reaction to Acids — Edexcel International GCSE Science (Double Award) Chemistry (4WSD0-1C) Study Notes

Sign of a faster (more reactive) reaction

What you see / measure

More vigorous fizzing

More/bigger bubbles, faster

More gas given off per second

Gas syringe fills faster

Bigger temperature rise

Thermometer reads higher (exothermic)

Metal disappears sooner

Shorter time to dissolve

Keep the same (control variables)

Change (independent variable)

Measure (dependent variable)

Volume of acid

Type of metal

Volume of gas / temperature rise / time

Concentration of acid

Mass of metal

Surface area of metal (same size pieces)

Temperature at the start

Metal

Observation

Reactivity

Magnesium

Very vigorous fizzing; fast; large temperature rise

Most reactive

Zinc

Steady fizzing

Iron

Slow, gentle fizzing

Copper

No reaction at all

Least reactive

Results are often plotted as volume of gas against time. You must be able to read these graphs.

A steeper line and a faster level-off both mean a more reactive metal. All three level off at the same final volume because the same mass of metal was used.

How to read it:

Steeper line at the start = faster reaction = more reactive metal. Magnesium is steepest, so it is the most reactive.
The line levels off when the reaction has finished (one reactant is used up). The steepest curve also flattens first.
All three reach the same final volume here because the same mass of metal was used — the metal type changes the speed, not the amount of gas.

Calculating average rate:

$\text{average rate} = \frac{\text{total volume of gas}}{\text{time taken}}$

For example, if 48 cm³ of hydrogen is collected in 60 s:

average rate = 48 ÷ 60 = 0.8 cm³/s.

A higher average rate means a faster, more reactive metal.

Investigating metals reaction to acids

Detailed Notes

What you’ll learn

How it’s examined

1Write the equation for metal + acid (Getting started)

2Test for the gas given off (Getting started)

3Make it a fair test (Building confidence)

4Predict which metal fizzes fastest (Building confidence)

5Rank metals from a gas-volume graph (Stretch)

6Calculate the average rate of reaction (Stretch)

Reactivity (of a metal)

Salt

Test for hydrogen

Fair test

Control variable

Independent variable

Dependent variable

Surface area

Average rate of reaction

Gas syringe

✕Writing 'metal + acid → salt' and forgetting the hydrogen

✕Saying a glowing splint relights for the hydrogen test

✕Forgetting surface area as a control variable

✕Writing 'use the same amount of acid' instead of volume AND concentration

✕Saying copper 'is just unreactive' without explaining why it gives no gas

✕Calculating average rate without converting minutes to seconds (or omitting the unit)

Past paper style quiz

Investigating metals reaction to acids

Detailed Notes

What you’ll learn

How it’s examined

1Write the equation for metal + acid (Getting started)

2Test for the gas given off (Getting started)

3Make it a fair test (Building confidence)

4Predict which metal fizzes fastest (Building confidence)

5Rank metals from a gas-volume graph (Stretch)

6Calculate the average rate of reaction (Stretch)

Reactivity (of a metal)

Salt

Test for hydrogen

Fair test

Control variable

Independent variable

Dependent variable

Surface area

Average rate of reaction

Gas syringe

✕Writing 'metal + acid → salt' and forgetting the hydrogen

✕Saying a glowing splint relights for the hydrogen test

✕Forgetting surface area as a control variable

✕Writing 'use the same amount of acid' instead of volume AND concentration

✕Saying copper 'is just unreactive' without explaining why it gives no gas

✕Calculating average rate without converting minutes to seconds (or omitting the unit)

Past paper style quiz