§4.3
Single displacement (Zn + Cu²⁺)
last week · Wed P5
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
DriverZn kicks Cu²⁺ out of solution.
What you seeBlue solution fades; brown Cu coats the Zn strip.
12P3
Fri 8 May
L12
§4.4
Week 3 · Lesson 9 of 17
Neutralisation and other reactions of acids — acid + metal
Drop a strip of magnesium into dilute hydrochloric acid and the metal vanishes in front of you, releasing bubbles of hydrogen gas. Today you'll learn the general rule for acid + metal reactions and the textbook reactivity series (Table 4.3) that tells you which metals react fast, slow, or not at all.
Learning Intentions + Success Criteria
LITo describe the reaction of an acid with a metal and predict its rate using the reactivity series.
SC: I can:
- 01I can write the general word equation: acid + metal → salt + hydrogen gas.
- 02I can use Table 4.3 (reactivity series) to predict whether a given metal reacts with dilute acid and how vigorously.
- 03I can name the salt produced when a given acid reacts with a given metal.
Engage
5 minQuick recap · from last class
L11 · §4.4 Neutralisation and other reactions of acids — neutralisation
Try these 2questions before today's new content. Click an answer for instant feedback — your teacher will walk through them with you.
Predict · your turn
Write before you watch
Magnesium ribbon is placed in dilute hydrochloric acid. The metal fizzes and disappears, and a gas is released. What two products do you think are formed?
Explicit
17 minToday's procedure — predicting acid + metal reactions
START — metal M placed in dilute acid HX
1. Identify M (free metal) and HX (acid)
Mg in HCl → M = Mg, acid anion = Cl⁻
2. Find M on the Activity Series
Table 4.3 in your textbook (also in the Toolbox panel)
3. Is M ABOVE hydrogen on the series?
↓ No
No reaction.
M is less reactive than H — it can't displace H from the acid.
e.g. Cu + HCl: nothing happens
M is less reactive than H — it can't displace H from the acid.
e.g. Cu + HCl: nothing happens
↓ Yes
M displaces H!
Products = salt + H₂(g) (hydrogen gas):
Products = salt + H₂(g) (hydrogen gas):
Mg(s) + 2 HCl(aq)
→ MgCl₂(aq) + H₂(g)
magnesium + hydrochloric acid → magnesium chloride + hydrogen gas→ MgCl₂(aq) + H₂(g)
↻ Pattern bridge · §4.3 → §4.4single displacement family
One pattern, two contexts
A + BC → AC + BA free element kicks another out of a compound.
§4.4you are here
Acid + metal
Fri 8 May · P3
Mg(s) + 2 HCl(aq) → MgCl₂(aq) + H₂(g)
DriverMg kicks H out of HCl. Hydrogen escapes as a gas.
What you seeBubbles of H₂; metal dissolves; squeaky pop on lit splint.
Take-awayThe rule never changes: the free element must sit above the displaced element on the activity series (Table 4.3). Last week it was Zn vs Cu²⁺. This lesson it is Mg vs H⁺ — same skill, new partners.
↗ See alsoTwo of the other three reactions of acids — acid + base and acid + oxide — sit in the double-displacement family (ions swap partners; see L8 Fri 8 May P2 and L10 Tue 12 May P4). Acid + metal carbonate is in neither family: Good Science Table 4.4 lists it as its own pattern (three products: salt + water + CO₂; L10 Tue 12 May P4).
Acids react with metals to produce salts and hydrogen gas
Acids react with metals. Some metals are more reactive than others. You can see this in the activity series of metals in Table 4.3. The metals at the top of the reactivity series, such as potassium and sodium, react violently, while those at the bottom react very little. This is one reason that gold and silver are used to make jewellery, rather than iron and zinc. Gold and silver are fairly unreactive, so they keep their shiny surface even when exposed to acids and oils in the air or on your skin.
Acids react with metals to form salts and hydrogen gas. More reactive metals react faster, which you can see by how quickly the hydrogen gas bubbles are released.
acid+metal⟶salt+hydrogen
The salt formed depends on the acid the metal reacts with. For example, magnesium reacts with hydrochloric acid to produce magnesium chloride and hydrogen gas.
2HCl(aq)+Mg(s)⟶MgCl2(aq)+H2(g)
Word form: hydrochloric acid + magnesium → magnesium chloride + hydrogen.
Table 4.3 — The reactivity of different metals with acids
| Metal | Reactivity |
|---|---|
| Potassium (K) | ↑ Most reactive |
| Sodium (Na) | ↑ |
| Calcium (Ca) | ↑ |
| Magnesium (Mg) | ↑ |
| Aluminium (Al) | ↑ |
| Zinc (Zn) | ↑ |
| Iron (Fe) | ↓ |
| Tin (Sn) | ↓ |
| Lead (Pb) | ↓ |
| Copper (Cu) | ↓ |
| Silver (Ag) | ↓ |
| Gold (Au) | ↓ Least reactive |
Note: this is Table 4.3 from §4.4 (12 metals). It is similar to but not identical to Figure 4.9 from §4.3 (16 metals); for Yr 10 we use whichever the textbook references in each section.
Samples of magnesium, zinc, iron and lead each react differently if placed in a hydrochloric acid solution. Magnesium reacts vigorously to produce magnesium chloride and hydrogen gas, visible as bubbles. Zinc and iron react less vigorously with the acid, and release hydrogen gas bubbles more slowly than the magnesium. Lead is relatively unreactive, so no gas bubbles are seen (Lead is at the bottom of the reactivity series in Table 4.3, indicating it reacts very slowly).
Figure 4.19 — Magnesium, zinc, iron and lead in dilute HCl: bubble density tracks the activity series. Mg fizzes vigorously; Zn moderately; Fe slowly; Pb (below H) does not react.
Figure 4.20 — Potassium sits further up the activity series than calcium: K reacts with cold water producing enough heat to ignite the hydrogen, while Ca only fizzes. Both are well above Mg, which barely reacts with cold water at all.
Lab safety — handling acids in the lab
Even dilute lab acids can burn skin and eyes. Three rules to follow every time you handle them:
-
Diluting a strong acid: pour the ACID into the WATER, never the other way around. Adding water to concentrated acid releases a lot of heat at the surface and can boil and spit acid back at you. Adding acid into a larger volume of water disperses the heat safely.
-
If acid splashes on skin: rinse with plenty of cold water for at least a minute, then tell the teacher. Don't wipe with a dry paper towel — that smears the acid into the skin. Don't try to neutralise with bicarbonate or another base — water dilution is the immediate first response; the teacher decides what comes next.
-
PPE for any acid work: safety glasses + gloves + protective clothing (lab coat or apron). Glasses alone are not enough when handling concentrated or strong acid; gloves alone don't protect your eyes. The combination is the only safe setup.
Look for the corrosive pictogram (red diamond, hand and surface being eaten) on the bottle. If a bottle carries it, treat the contents as concentrated until proven otherwise — read the label, ask the teacher.
Key terms
Keywords
- acid
- A substance with a pH of less than 7.
- alkali
- A base that is dissolved in water.
- base
- A substance with a pH of more than 7.
- caustic
- Able to burn or corrode organic tissue through chemical action.
- concentration
- The amount of a substance in a volume of solution.
- corrosive
- Highly reactive and damaging or destructive to another substance.
- indicator
- A substance used to determine the acidity of a solution.
- neutralisation reaction
- A reaction involving an acid and a base to produce water and a salt.
- neutralise
- To make something chemically neutral; neither acidic nor basic.
- pH
- A figure expressing the acidity or alkalinity of a solution.
We do — predict two metals, side-by-side
We do · whole class · 3 prompts
A student tests two metals — Cu and Mg — by dropping each into a beaker of dilute HCl(aq). Predict what happens to each.
Prompt 1 — locate Cu, Mg, and H on Table 4.3 (open the Toolbox).
Prompt 2 — apply the rule: which one(s) react with dilute HCl?
Prompt 3 — for the metal that reacts, write the balanced equation with state symbols.
Watch out · common traps
Trap 1
“Copper reacts with dilute HCl.”
Wrong — copper is below hydrogen on the activity series (Table 4.3), so it cannot displace H from the acid. Drop a copper coin into vinegar and it just sits there.
The same is true for silver and gold — that is why we use them for jewellery, coins, and contact pins. They survive being splashed by everyday weak acids in the air, sweat, and food.
Rule: only metals above hydrogen on Table 4.3 react with dilute acid. Cu, Ag, Au are out.
Trap 2
“Mg + HCl → MgCl + H₂.”
Wrong — magnesium forms an Mg²⁺ ion, so the salt must be MgCl₂, not MgCl. And one Mg²⁺ needs two Cl⁻ ions, so we need 2 HCl to provide them.
Mg(s)+2HCl(aq)⟶MgCl2(aq)+H2(g)
The same trap appears with aluminium: Al forms Al³⁺, so the salt is AlCl₃ and the equation needs 6 HCl to give 2 AlCl₃ + 3 H₂.
Rule: write the salt formula from the metal's ion charge first, then balance the H atoms.
Trap 3
“Acid + metal gives salt + water.”
Wrong — that's neutralisation (acid + base → salt + water). Acid + metal gives salt + hydrogen GAS. Don't mix up the second product across the four reactions of acids you'll meet in §4.4:
| Reaction | Second product |
|---|---|
| acid + base | water |
| acid + metal | hydrogen gas (H₂) |
| acid + metal carbonate | water + CO₂ |
| acid + metal oxide | water |
Rule: acid + metal → salt + H₂(g) — confirmed by the squeaky-pop test.
Apply
25 minZinc metal reacts with dilute hydrochloric acid. Fill in the blanks to complete the word equation:
The balanced symbol equation:
2HCl(aq)+Zn(s)⟶ZnCl2(aq)+H2(g)
Your turnShort answer · Have a go first
A student places equal-sized strips of zinc, iron, and copper in three test tubes of dilute hydrochloric acid. Predict in which order they release hydrogen gas (fastest to slowest), and use Table 4.3 to justify your prediction.
(Each reaction also produces hydrogen gas as the second product.)
Catch
5 minReflect
10 minYour turnReflect · One thing you learned
One thing I now understand about acid + metal reactions, or the reactivity series in Table 4.3, that I didn't understand before:
Success criteria — where are you right now?
Next class (Tue 12 May, P4): acid + metal carbonate and acid + metal oxide — the last two of the four reactions of acids.