7.2Acids, Bases and Salts
Oxides — Combined Science 0653 - Chemistry Revision Notes & Topical Questions
5 min read 11 parts Lesson 5 of 8 1 quiz
Lesson summary
7.2 Oxides — COMBINED SCIENCE (CHEMISTRY) notes: Classify oxides as acidic or basic by metallic and non-metallic character.Oxide — = compound of oxygen with one other element.Examples are MgO, ZnO, K2O, CO2, SO2 and H2O.Classification — oxides are classified by their acid-base be…
- Acidic oxide
- Basic oxide
- Neutralisation
- Classification — oxides are classified by their acid-base behaviour
- Formed by — a non-metal combining with oxygen
- Reactions — they react with bases to form a salt and water
Section 1 of 11What oxides are
What oxides are
Oxide
- = compound of oxygen with one other element.
- Examples are MgO, ZnO, K2O, CO2, SO2 and H2O.
Classification
- Classification oxides are classified by their acid-base behaviour.
Section 2 of 11Acidic oxides
Formed by
- Formed by a non-metal combining with oxygen.
Reactions
- Reactions they react with bases to form a salt and water.
In water
- In water they give an acidic solution with a low pH.
Examples
- CO2, SO2, NO2 and SiO2.
Section 3 of 11Basic oxides
Formed by
- Formed by a metal combining with oxygen.
Reactions
- Reactions they react with acids to form a salt and water.
In water
- In water those that dissolve give a basic solution with a high pH.
Examples
- CuO and CaO.
Section 4 of 11Metal and non-metal oxides
| Feature | Basic oxide | Acidic oxide |
|---|---|---|
| Element | Metal | Non-metal |
| Reacts with | Acids | Bases |
| Solution pH | High | Low |
| Examples | CuO, CaO | CO2, SO2 |
- Rule
- metals form basic oxides and non-metals form acidic oxides.
Section 5 of 11More from the specification
More from the specification
Basic oxides
- Metallic oxides that react with acids to undergo neutralisation and form salts plus water.
- (such as magnesium oxide)
Acidic oxides
- Non-metallic oxides (such as SO2 and CO2) that react with alkalis or water to form acidic solutions.
Amphoteric and neutral oxides
- Oxides like aluminium oxide react with both acids and bases;
- neutral oxides like CO and NO show no acid-base properties.
Indicators
- Substances like litmus or universal indicator that show distinctive colour changes according to pH scale values.
Property
- A feature that describes what a substance is like and what it does.
Strong acid
- An acid that is completely dissociated in water.
Carbon dioxide
- A gas that turns limewater cloudy.
Proton transfer
- Movement of H+ from acid to base.
Amphoteric oxide
- An oxide that reacts with both acids and bases.
Methyl orange
- Indicator with range about pH 3.2 to 4.4, red to yellow.
Universal indicator
- Mixture of indicators giving a range of colours.
Concentration
- Moles ÷ volume in dm³, or g/dm³.
Hydrogen
- A gas that gives a squeaky pop with a lighted splint.
Alkali
- A soluble base that produces OH− ions in water.
Neutralisation
- The reaction of an acid with a base to form a salt and water.
Indicator
- Substance whose colour depends on pH.
Proton
- Positive particle in the nucleus.
Hydroxide
- A compound containing the OH− ion, formed by Group I metals with water.
Litmus
- Dye that is red in acid, blue in alkali and purple in neutral.
Section 6 of 11Neutral oxides
- Neutral oxide
- an oxide that reacts with neither acids nor bases.
- Examples are N2O, NO and CO.
- Water is also commonly classed as neutral.
Section 7 of 11Amphoteric oxides (supplement)
Amphoteric oxide
- Amphoteric oxide an oxide that behaves as an acid or a base depending on the other reactant.
- Zinc oxide and aluminium oxide are the two common examples.
- Their hydroxides are also amphoteric.
Products
- Products in both cases a salt and water are formed.
Section 8 of 11Aluminium oxide as a base and as an acid
| Role | Reactant | Equation |
|---|---|---|
| Base | Acid (HCl) | Al2O3 + 6HCl → 2AlCl3 + 3H2O |
| Acid | Alkali (NaOH) | Al2O3 + 2NaOH → 2NaAlO2 + H2O |
Section 9 of 11More from the specification
More from the specification
Acidic, basic, and amphoteric oxides
- Basic metallic oxides react with acids to form salts and water;
- acidic non-metallic oxides dissolve in water to form acidic solutions;
- amphoteric oxides react with both acids and bases.
Neutralisation reactions and net ionic equations
- Mixing aqueous hydrochloric acid with basic metal oxides or hydroxides yields neutralisation: H+(aq) + OH−(aq) → H2O(l).
Reaction of magnesium oxide with acids
- Solid magnesium oxide reacts with dilute sulfuric acid to form soluble magnesium sulfate and water: MgO(s) + H2SO4(aq) → MgSO4(aq) + H2O(l).
pH logarithmic scale
- pH logarithmic scale every single unit decrease on the pH scale represents a tenfold increase in aqueous hydrogen ion concentration.
Strong versus weak acids
- Strong versus weak acids hydrochloric acid dissociates fully in aqueous solution, whereas weak acids dissociate partially at identical molarity.
Acid-base neutralisation
- Acid-base neutralisation hydrogen ions react with hydroxide ions to form neutral water molecules, detectable by universal indicator colour changes.
Property
- A feature that describes what a substance is like and what it does.
Strong acid
- An acid that is completely dissociated in water.
Carbon dioxide
- A gas that turns limewater cloudy.
Proton transfer
- Movement of H+ from acid to base.
Methyl orange
- Indicator with range about pH 3.2 to 4.4, red to yellow.
Universal indicator
- Mixture of indicators giving a range of colours.
Concentration
- Moles ÷ volume in dm³, or g/dm³.
Neutralisation
- The reaction of an acid with a base to form a salt and water.
Indicator
- Substance whose colour depends on pH.
Proton
- Positive particle in the nucleus.
Litmus
- Dye that is red in acid, blue in alkali and purple in neutral.
Section 10 of 11Key terms
| Term | Meaning |
|---|---|
| Oxide | Compound of oxygen and one other element. |
| Acidic oxide | Non-metal oxide that reacts with bases. |
| Basic oxide | Metal oxide that reacts with acids. |
| Salt | Product of an acid reacting with a base. |
| Neutralisation | Reaction of an acid with a base. |
| Term | Meaning |
|---|---|
| Neutral oxide | Oxide that reacts with neither acids nor bases. |
| Amphoteric oxide | Oxide that reacts with both acids and bases. |
| Acidic oxide | Non-metal oxide that reacts with bases. |
| Basic oxide | Metal oxide that reacts with acids. |
| Hydroxide | Compound containing the OH^{-} ion. |
Section 11 of 11Exam technique
1
Saying all oxides are acidic.
2
Mixing up which type of oxide reacts with acids — basic oxides react with acids.
3
Saying non-metals form basic oxides.
4
Forgetting that a salt and water are formed in both reactions.
1
Classifying aluminium oxide as acidic only — it is amphoteric.
2
Saying neutral oxides form acids with water.
3
Mixing up metal and non-metal oxide types.
4
Writing water as a product incorrectly for amphoteric reactions.
Marked practiceQuizzes for this lesson
Last updated: