2.2.3Chemical Bonding, Application Of Chemical Reactions and Organic Chemistry
Acids Reacting with Metals
5 min read 6 parts Lesson 16 of 54 1 quiz
Section 1 of 6Which metals react?
Reactivity series rule
- Reactivity series rule Only metals above hydrogen in the reactivity series react with dilute acids.
- Copper is below hydrogen, so it does not react.
Vigour of reaction
- Vigour of reaction The higher the metal in the series, the more vigorous the reaction.
- Potassium and sodium react explosively and are far too dangerous to add to acid.
General equation
- General equation metal + acid → salt + hydrogen. A way to remember this is MASH: Metal, Acid, Salt, Hydrogen.
Section 2 of 6Equations to know
| Metal | With sulfuric acid | With hydrochloric acid |
|---|---|---|
| Magnesium | Mg(s) + H2SO4(aq) → MgSO4(aq) + H2(g) | Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) |
| Zinc | Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g) | Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) |
| Iron | Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g) | Fe(s) + 2HCl(aq) → FeCl2(aq) + H2(g) |
Section 3 of 6Observations and the hydrogen test
What you see
- What you see The metal fizzes as bubbles of gas form, and the metal gradually disappears.
- The test tube often becomes warm because the reaction gives out heat.
Test for hydrogen
- Test for hydrogen Hold a lighted splint at the mouth of the test tube.
- Hydrogen burns with a squeaky pop.
Section 4 of 6Making crystals of zinc sulfate
1
Add zinc to dilute sulfuric acid: Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g).
2
Make sure the zinc is in excess so that all of the acid is used up.
3
Wait until the fizzing stops, which shows the reaction has finished.
4
Filter the mixture into a beaker to remove the unreacted zinc.
5
Heat the filtrate gently until about half the solution is left and crystals begin to form on the edge or a glass rod.
6
Leave the solution to cool, pour it into an evaporating dish and place it in a warm oven or leave it to dry so that crystals form fully.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Reactivity series | A list of metals in order of how readily they react. |
| Salt | A compound formed when the hydrogen of an acid is replaced by a metal. |
| Excess | More of a reactant than is needed, so that some is left over. |
| Filtrate | The solution that passes through the filter paper. |
| Crystallisation | Formation of solid crystals as a solution is concentrated or cooled. |
Section 6 of 6Exam technique
1
Heating the solution to dryness in the beaker — this can decompose the crystals, so stop when crystals begin to form and let the rest evaporate gently.
2
Using copper with dilute acid and expecting hydrogen — copper is below hydrogen and does not react.
3
Forgetting to balance the equationhydrochloric acid needs a 2 in front of HCl.
4
Writing 'hydrogen is produced' as the observation — the observation is fizzing or bubbles.