5.7Chapter 5: Acids and Alkalis
Chapter 5 Review: Acids and Alkalis — Alhussan Chemistry - Stage 7 Revision Notes & Topical Questions
5 min read 9 parts Lesson 7 of 7 2 quizzes
Lesson summary
5.7 Chapter 5 Review: Acids and Alkalis — Alhussan International Academy — Chemistry (Stages 7–9) notes: Revise acids, alkalis, pH, indicators, neutralisation, acid rain and gas tests from Chapter 5.Acids — they have pH below 7, taste sour, turn litmus red and contain hydrogen io…
- Universal indicator
- Measuring pH
- Not all acids are dangerous
- Making a cabbage indicator
- Salt families
- Dilution and neutralisation
Section 1 of 9Acids, alkalis and the pH scale
Acids, alkalis and the pH scale
Acids
- Acids they have pH below 7, taste sour, turn litmus red and contain hydrogen ions.
Alkalis
- Alkalis they have pH above 7, feel soapy, turn litmus blue and contain hydroxide ions.
Neutral
- Neutral a neutral solution has pH 7.
Universal indicator
- Universal indicator its colour changes across the pH range: red, orange, yellow, green, blue, purple from acid to alkali.
Measuring pH
- Measuring pH a pH meter is more precise, and litmus only shows whether something is acidic or alkaline.
Safety
- Safety concentrated or strong acids and alkalis are corrosive and need careful handling with eye protection.
Not all acids are dangerous
- Not all acids are dangerous many food acids are safe.
Section 2 of 9Indicators and everyday pH
Indicators and everyday pH
Making a cabbage indicator
- Making a cabbage indicator heat a mixture of pure water and chopped cabbage in a beaker, filter the mixture and add the indicator to small amounts of acid and alkali.
Litmus
- Litmus it is red in acid, and adding enough alkali turns it purple at neutral and then blue.
Blood
- Blood it is slightly alkaline.
Teeth
- Teeth they are damaged when the pH of saliva falls to 5 or below.
Farming
- Farming a farmer who wants to grow bananas on acidic soil should add an alkali.
Section 3 of 9Neutralisation and salts
Neutralisation and salts
Equation
- Equation acid + alkali → salt + water, and ionically H+ + OH− → H2O.
Salt families
- Salt families hydrochloric acid gives chlorides, sulfuric acid sulfates and nitric acid nitrates.
Uses
- Uses antacids for indigestion, treating acid soils with lime, and making salts such as copper sulfate.
- Copper sulfate is made by adding excess copper oxide to sulfuric acid, filtering and crystallising.
Titration
- Titration it finds how much acid neutralises a measured volume of alkali, using a burette and an indicator, and repeated runs give concordant results.
Dilution and neutralisation
- Dilution and neutralisation dilution raises the pH only towards 7, whereas neutralisation can pass 7 if excess alkali is added.
Section 4 of 9Gases and tests
| Reaction | Products | Test |
|---|---|---|
| Acid + metal | Salt + hydrogen | Lighted splint: squeaky pop |
| Acid + carbonate | Salt + water + carbon dioxide | Limewater turns cloudy |
| Acid + alkali | Salt + water | Temperature rise, pH to 7 |
- Oxygen
- it relights a glowing splint.
Section 5 of 9Acid rain and the environment
Formation
- Formation sulfur dioxide and nitrogen oxides dissolve in rainwater, and cars as well as factories produce them.
Damage
- Damage it harms lakes, trees and limestone buildings.
Reducing it
- Reducing it remove sulfur from fuels, desulfurise flue gases, use catalytic converters and switch to cleaner energy.
Liming
- Liming it neutralises damaged lakes and soils but treats the symptom rather than the cause.
Section 6 of 9The key idea
The key idea
Acids contain hydrogen ions and alkalis contain hydroxide ions.
This explains the pH scale, indicator colours, reactions with metals and carbonates, and why neutralisation produces water.
Section 7 of 9Practical skills
Practical skills
Plan a fair test with independent, dependent and control variables.
Use correct units such as cm3 and write a gas test with its result.
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Acid | A substance with pH below 7 that contains hydrogen ions. |
| Alkali | A soluble base with pH above 7 that contains hydroxide ions. |
| Neutralisation | A reaction between an acid and an alkali that makes a salt and water. |
| Titration | Adding one solution to another until the reaction is just complete. |
| Acid rain | Rain made acidic by sulfur dioxide and nitrogen oxides. |
| Universal indicator | A mixture of dyes showing pH by colour. |
Section 9 of 9Exam technique
1
Mixing up hydrogen and carbon dioxide tests.
2
Thinking neutralisation makes only water — it also makes a salt.
3
Believing acid rain is caused by carbon dioxide only.
4
Not stating the colour for a positive result.
Marked practiceQuizzes for this lesson
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