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4.2.1Chemical Changes

Metal and acid — AQA GCSE Combined Science Trilogy 8464 - Chemistry Revision Notes & Topical Questions

5 min read 7 parts Lesson 6 of 18

📚 AQA GCSE Combined Science Trilogy 8464 - Chemistry Hub / Topical Revision
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Part 1 of 5Which metals react

Above hydrogen only
  • Above hydrogen only Only metals above hydrogen in the reactivity series displace hydrogen from dilute acids.
  • Copper, silver and gold lie below hydrogen, so they do not react with dilute acids.
Reactivity and vigour
  • Reactivity and vigour The higher the metal in the series, the faster the bubbling and the greater the temperature rise.
  • Magnesium fizzes quickly, zinc moderately and iron slowly.
Too dangerous to try
  • Too dangerous to try Potassium and sodium react explosively with acids, so they are never used in a school laboratory for this reaction.

Part 2 of 5General pattern

metal + acid → salt + hydrogen
Hydrochloric acid
  • Hydrochloric acid Always gives a chloride salt, for example magnesium chloride.
Sulfuric acid
  • Sulfuric acid Always gives a sulfate salt, for example zinc sulfate.
Nitric acid
  • Nitric acid Gives nitrates, but reactions are more complex, so it is rarely used for this reaction at GCSE.
Hydrogen gas
  • Hydrogen gas The bubbles are hydrogen, confirmed by a lit splint making a squeaky pop.

Part 3 of 5Equations to know

MetalWith hydrochloric acidWith sulfuric acid
MagnesiumMg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)Mg(s) + H2SO4(aq) → MgSO4(aq) + H2(g)
ZincZn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)
IronFe(s) + 2HCl(aq) → FeCl2(aq) + H2(g)Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)

Part 4 of 5Writing an equation for any metal

1
Check the metal is above hydrogen in the reactivity series; if not, write 'no reaction'.
2
Name the salt: metal name first, then chloride, sulfate or nitrate depending on the acid.
3
Write the formula of the salt using the charge on the metal ion.
4
Add hydrogen as H2(g) on the product side.
5
Balance the equation, adding state symbols (s), (aq) and (g).

Part 5 of 5What you observe

1Metal added
  • Metal added The solid begins to bubble on its surface.
2Gas forms
  • Gas forms Hydrogen is released, and the metal gradually gets smaller.
3Heat released
  • Heat released The test tube warms up because the reaction is exothermic.
4Metal disappears
  • Metal disappears A colourless solution of the salt is left (iron salts give a pale green solution).

Key terms

TermMeaning
Reactivity seriesA list of metals in order of how readily they react.
SaltA compound formed when the hydrogen of an acid is replaced by a metal ion.
DisplacementA reaction in which a more reactive element takes the place of a less reactive one in a compound.
Squeaky pop testThe test for hydrogen: a lit splint makes a small popping sound.
Dilute acidAn acid containing a relatively small amount of acid dissolved in a large volume of water.

Avoid these mistakes

1
Saying copper reacts slowly with dilute hydrochloric acid — it does not react at all.
2
Writing hydrogen as H instead of H2 in the products.
3
Using the wrong saltsulfuric acid gives sulfates, hydrochloric acid gives chlorides.
4
Describing the squeaky pop as a test for oxygen; oxygen relights a glowing splint.

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