Unit 8: Energy changes and reactions of metals
Metals and their reactions — HIA International - Grade 7 Revision Notes & Topical Questions
5 min read 9 parts Lesson 4 of 12 1 quiz
Lesson summary
8.3 Metals and their reactions with oxygen, water and acids — HIA INTERNATIONAL notes: Compare the reactivity of metals using their reactions with oxygen, water, steam and dilute acids.Reactivity — shown by how quickly or vigorously a metal reacts.Example — magnesium is more reac…
- Uncombined
- General equation
- Sodium, potassium and calcium
- Oxide layer
- Calcium and magnesium
- Observations
Section 1 of 9Reactivity of metals
Reactivity
- Reactivity shown by how quickly or vigorously a metal reacts.
Example
- Example magnesium is more reactive than iron because it reacts more quickly.
Inert
Inert unreactive, as gold is.
Uncombined
- Uncombined gold and silver are found as pure metals because they are unreactive.
Section 2 of 9Metal and oxygen
General equation
- General equation metal + oxygen gives metal oxide.
Oxidation
Oxidation a reaction in which a substance combines with oxygen.
Sodium, potassium and calcium
- Sodium, potassium and calcium react with air without heating, so cut surfaces turn dull quickly and they are stored under oil.
Oxide layer
- Oxide layer on the surface stops more of the metal reacting.
Silver
- Silver reacts slowly and goes black as silver oxide forms.
Section 3 of 9Metal and water
General equation
- General equation metal + water gives metal hydroxide + hydrogen.
Sodium
- Sodium reacts vigorously, e.g. sodium + water gives sodium hydroxide + hydrogen.
Potassium
- Potassium more reactive, so much heat is produced that the hydrogen burns.
Calcium and magnesium
- Calcium and magnesium react less vigorously, and the gas can be collected in a test tube by displacement of water.
Steam
- Steam magnesium reacts more rapidly with steam than with water, giving magnesium oxide and hydrogen.
Gold
- Gold does not react with water at all.
Section 4 of 9Metal and dilute acid
General equation
- General equation metal + acid gives salt + hydrogen.
Examples
- Examples magnesium + hydrochloric acid gives magnesium chloride + hydrogen;
- zinc + sulfuric acid gives zinc sulfate + hydrogen.
Salts
- Salts hydrochloric acid makes chlorides, sulfuric acid sulfates and nitric acid nitrates.
Observations
- Observations bubbles of hydrogen, the metal shrinks and the mixture warms.
Test for hydrogen
- Test for hydrogen a lit splint gives a squeaky pop.
Section 5 of 9Reactivity order
More reactive
- More reactive potassium, sodium, calcium, magnesium.
Middle
- Middle zinc, iron.
Less reactive
- Less reactive copper, silver, gold.
Placing metals
- Placing metals the more vigorous the reactions with oxygen, water and acid, the higher the metal.
Unsuitable metals
- Unsuitable metals sodium, potassium and calcium are too dangerous in acid, and gold and silver do not react.
Section 6 of 9Investigating reactivity in acid
1
Choose safe metals and wear safety glasses, gloves and a face protector.
2
Add the same volume of the same acid to a test tube for each metal.
3
Add equal-sized pieces of each metal, one at a time.
4
Observe the bubbling and temperature for each.
5
Rank the metals from most to least reactive.
- Variable to change
- the metal; variables to keep the same — acid type, concentration and volume, metal size and temperature.
Section 7 of 9Rusting
Rust
Rust orange-brown iron oxide formed when iron reacts with oxygen and water.
Word equation
- Word equation iron + oxygen gives iron oxide.
Conditions
- Conditions both water and oxygen must be present, and the reaction is slow.
Rust test
- Rust test nails rust in moist air and in water and air, but not in dry air or in boiled water with oil on top.
Harm
- Harm rusting weakens iron girders and structures.
Protection
- Protection painting, oiling and galvanising.
- (coating with zinc)
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Reactivity | How readily a metal reacts. |
| Oxidation | A reaction in which a substance combines with oxygen. |
| Inert | Unreactive. |
| Salt | A compound formed when a metal replaces hydrogen in an acid. |
| Hydroxide | A compound of a metal with oxygen and hydrogen. |
| Rust | Iron oxide formed on iron in damp air. |
| Galvanising | Coating iron with zinc. |
| Steam | Water in the form of a hot gas. |
Section 9 of 9Exam technique
1
Saying gold reacts with oxygen — it is inert.
2
Saying rusting needs only oxygen — it needs water too.
3
Saying copper reacts with dilute acid — it does not.
4
Saying more reactive metals react slowly.
Marked practiceQuizzes for this lesson
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