Measurement and separation
Measure volume and use the five prescribed separation techniques in familiar settings. 2 reviewed objectives.
G1 Science Chemistry Revision Guide
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K123 G1 Science Chemistry revision guide covering measurement, separation, chemical changes, indicators, pH, neutralisation and prescribed gas tests.
Fast revision method
Cover the right-hand column of each table, say the answer aloud, then check it. G1 Chemistry is part of Food Chemistry, so every item below stays within the K123 course.
1. Measurement and Separation
| Task | Method or apparatus | Key idea |
|---|---|---|
| Measure liquid volume | measuring cylinder | Read the scale at eye level. |
| Measure an irregular solid | water displacement in a measuring cylinder | Volume of solid = final reading − initial reading. |
| Separate an insoluble solid from a liquid | filtration | The solid is the residue; the liquid that passes through is the filtrate. |
| Obtain a dissolved solid from a solution | evaporation | The solvent escapes and the dissolved solid remains. |
| Obtain a solvent from a solution | simple distillation | Evaporate the solvent, then cool its vapour to condense it. |
| Separate coloured substances in a mixture | paper chromatography | Different substances travel different distances with the solvent. |
| Make a substance dissolve faster | stir, warm, or use smaller pieces | These changes speed up dissolving; they do not increase the final amount that must always dissolve. |
Choose by the substance you need
Use evaporation when you need the dissolved solid. Use distillation when you need to collect the solvent. Use filtration only when the solid is insoluble.
2. Physical and Chemical Changes
| Type of change | What happens | Examples |
|---|---|---|
| Physical change | No new substance forms. It is often reversible. | melting ice, dissolving sugar, boiling water |
| Chemical change | One or more new substances form. It is often difficult to reverse. | cooking an egg, burning, rusting, food decay |
Evidence of a chemical reaction can include a lasting colour change, gas formation, a temperature change, light, or a new solid. One observation alone must be interpreted in context: boiling also makes bubbles, but it is a physical change.
Slowing unwanted chemical changes
- Refrigeration slows food decay.
- Airtight packaging reduces contact with oxygen and microorganisms.
- Dry storage reduces the water available for spoilage.
- Painting or coating iron keeps out oxygen and water, slowing rusting.
3. Acids, Alkalis, Indicators and pH
| Solution | pH | Litmus | Universal indicator |
|---|---|---|---|
| acidic | below 7 | blue litmus turns red | red, orange or yellow |
| neutral | 7 | no change | green |
| alkaline | above 7 | red litmus turns blue | blue or violet |
- An acid gives an acidic solution in water.
- An alkali gives an alkaline solution in water.
- An indicator changes colour to show whether a solution is acidic, neutral or alkaline.
- A lower pH means more acidic; a higher pH means more alkaline.
Indicator wording
Litmus tells you acid or alkali. Universal indicator or a pH meter gives more information about pH. Do not claim that litmus gives an exact pH.
4. Acid Reaction Patterns
| Reaction | General products | Observation to remember |
|---|---|---|
| acid + metal | salt + hydrogen | bubbles; hydrogen gives a squeaky pop with a lighted splint |
| acid + base | salt + water | the acid is neutralised |
| acid + carbonate | salt + water + carbon dioxide | bubbles; carbon dioxide turns limewater milky |
Neutralisation is the reaction in which an acid and a base react to form salt and water.
Everyday applications
- Antacids contain bases that neutralise excess stomach acid.
- Toothpaste helps neutralise acids that can damage teeth.
- A suitable base can reduce excess acidity in soil.
5. High-Value Mistakes to Fix
| Tempting answer | Why it loses marks | Better answer |
|---|---|---|
| “The solid disappears, so it melted.” | Dissolving and melting are different processes. | It dissolved and formed a solution. |
| “Filtration separates salt solution.” | Dissolved salt passes through filter paper. | Use evaporation for the salt or distillation for the water. |
| “Bubbles prove a chemical reaction.” | Boiling also forms bubbles. | Name the gas test or other evidence that a new substance formed. |
| “pH 7 is weakly acidic.” | pH 7 is neutral. | Values below 7 are acidic; values above 7 are alkaline. |
| “Acid + metal makes carbon dioxide.” | The gas pattern is wrong. | Acid + metal makes hydrogen; acid + carbonate makes carbon dioxide. |
6. Three Checks Before Practice
- Can you choose filtration, evaporation, distillation or chromatography and explain why?
- Can you distinguish a physical change from a chemical change using evidence?
- Can you state the three acid reaction patterns and the two prescribed gas tests?
Topic-by-Topic Revision
Use the summary above for recall, then open the full lesson when a point needs explanation or worked practice. Every topic below comes from this course’s reviewed objective map.
Chemical changes in food and materials
Recognise new-product formation and reason about slowing decay, cooking, burning and rusting. 1 reviewed objective.
Acids, alkalis and pH
Use indicators and pH, then apply the prescribed everyday acid reactions and neutralisation pattern. 2 reviewed objectives.