Lesson focus: Acids react with some metals to form a saltA compound made when an acid reacts with a base, such as sodium chloride (table salt). and hydrogen, with reaction rateHow fast something happens, such as how much changes each second or each minute. depending on both substances and the conditions.
Predict acid–metal products, use a reactivity seriesA list of metals in order from most reactive to least reactive. to explain observations and evaluate a gas-production investigation.
Build on earlier learning
Making saltsYear 8 made salts by neutralisation. This lesson extends salt formation to reactions between dilute acids and metals.
Practical
Metals and acid
- Add the same mass of magnesium, zinc and copper to equal volumes of dilute hydrochloric acid.
- Compare the rate of bubbling.
- Test the gas with a lit splint: a squeaky pop shows hydrogen.
Record: A table ranking the metals by how vigorously they react.
Safety: Wear eye protection.
You will be successful when you can…
- State the general acid–metal equation.
- Name chloride and sulfate salts correctly.
- Use the reactivity series to predict reaction extent.
- Evaluate hydrogen-rate evidence safely.
Words that carry the science
- reactivity series
- An ordering of metals by how readily they undergo chemical reactions.
- salt
- An ionic compound formed when the hydrogen ions of an acid are replaced by metal or ammonium ions.
- hydrogen test
- A lighted splint gives a squeaky pop when hydrogen is present.
- rate
- Change in a measured quantity divided by time.
- corrosive
- Able to damage living tissue or materials by chemical action.
- excess
- More reactant than is needed to react completely with the other reactant.
Connect metal reactivity to salt and hydrogen formation
01The products follow a reliable pattern
For suitable metals, acid + metal → salt + hydrogen. Hydrochloric acid forms chlorides; sulfuric acid forms sulfates. For example, magnesium + sulfuric acid → magnesium sulfate + hydrogen.
The acid supplies hydrogen ions. Metal atoms lose electrons and hydrogen ions gain electrons, although detailed half-equations belong to later study.
02Reactivity controls what can be observed
Magnesium reacts faster than zinc under matched conditions because magnesium is more reactive. Copper does not normally release hydrogen from dilute hydrochloric or sulfuric acid because it is below hydrogen in the reactivity seriesA list of metals in order from most reactive to least reactive..
A faster reaction can produce a steeper gas-volume graph, but the final volume depends on the amount of the limiting reactant, not just reactivity. Equal masses of different metals may contain different numbers of atoms.
03Measure gas safely and fairly
Collect hydrogen in a gas syringe and record volume at regular intervals. Keep metal amount and surface area, acid concentration and volume, and temperature controlled when comparing metals. Use dilute acid, eye protection and small quantities.
Hydrogen is flammable. Keep ignition sources away during collection; a teacher-controlled test can use only a small sample after the collection apparatus is safely disconnected. Check that a bung does not create an unsafe pressure if the outlet is blocked.
Metals reacting with acid
Some metals react with dilute acids to make a salt and hydrogen gas. Collect the hydrogen in a gas syringe: a more reactive metal gives off hydrogen faster. Copper is below hydrogen in the reactivity series, so it does not react. The animation runs ten times faster than real time.
Controls
Test for hydrogen: a lit splint gives a squeaky pop. Final volumes come from the masses; the rates are illustrative.
Name the salt and predict the gas
Zinc is added to dilute hydrochloric acid.
- Use acid + metal → saltA compound made when an acid reacts with a base, such as sodium chloride (table salt). + hydrogen.
- Hydrochloric acid produces a chloride salt.
- The metal is zinc, so the salt is zinc chloride.
- Write: zinc + hydrochloric acid → zinc chloride + hydrogen.
How to make the reasoning visible: Zinc is above hydrogen in the reactivity series, so hydrogen gas is expected under suitable conditions.
Interpret an acid–metal data set
Equal-length strips with matched surface condition react with the same volume and concentration of acid at 20 °C.
| Metal | Hydrogen after 30 s / cm³ | Final hydrogen / cm³ | Evidence | Interpretation |
|---|---|---|---|---|
| Magnesium | 42 | 48 | Rapid fizzing | Fastest here |
| Zinc | 16 | 47 | Steady fizzing | Slower, similar final volume |
| Iron | 5 | 44 | Slow fizzing | Slower still |
| Copper | 0 | 0 | No visible change | No hydrogen produced |
Why can magnesium and zinc have similar final volumes but different 30-second volumes?
Why should oxide coatings and metal surface area be controlled?
Check your understanding
Answer from memory, then check against the suggested answer.
State the general equation for an acid reacting with a metal.
What salt does sulfuric acid form?
What is the test for hydrogen?
A student replaces magnesium ribbon with magnesium powder. Predict the graph change.
Explain why equal masses of magnesium and zinc do not contain equal numbers of atoms.
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Equal-sized strips of magnesium and zinc are added to identical hydrochloric acid. Magnesium produces hydrogen faster.
Explain what this shows about the reactivity of magnesium and zinc.
(3)State two variables that must be controlled.
(2)Total for this question: 5 marks
Command word: For explainA command word: say how or why something happens, giving reasons with words like "because" or "so"., state the pattern, give the particle or reactivity reason, then protect the comparison with named control variables.