Food chemistry
Measuring volume, separating mixtures, chemical changes, indicators and pH, and acid reactions.
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Before you begin
Chemistry in the kitchen: measuring volumes, separating mixtures, identifying food dyes, recognising chemical changes and testing how acidic or alkaline foods are.
Be comfortable with: reading a scale, and the difference between a solid, a liquid and a gas.
Learning goals
- Measuring volume
- Dissolving
- Filtration
- Evaporation
- Distillation
- Everyday uses of separation
- Paper chromatography
- Chemical reactions
- Slowing food decay
- Slowing cooking and burning
- Slowing rusting
- Indicators
- Measuring pH
- The pH scale
- Acid and metal
- Acid and base
- Acid and carbonate
- Neutralisation
Syllabus statements covered
- use a measuring cylinder to measure volume of liquid/solid
- explain that substances can be separated from a mixture through the following techniques: — dissolving
- explain that substances can be separated from a mixture through the following techniques: — filtration
- explain that substances can be separated from a mixture through the following techniques: — evaporation
- explain that substances can be separated from a mixture through the following techniques: — distillation
- state some uses of separation techniques in homes and food industries (e.g. remove tea leaves from a cup of tea, obtain water from seawater)
- explain that substances can be separated from a mixture through the following techniques: — paper chromatography
- describe a chemical reaction as a process that leads to the formation of new products
- state the following everyday changes that involve chemical reactions and how they can be slowed down: — decaying of food slowed down by food preservation methods (see also LO 2.3(d))
- state the following everyday changes that involve chemical reactions and how they can be slowed down: — cooking of food and burning of fuel slowed down by reducing oxygen/fuel supply
- state the following everyday changes that involve chemical reactions and how they can be slowed down: — rusting of iron cans slowed down by tin-plating
- describe the properties of acids and alkalis in terms of their effects on litmus paper and universal indicator solution
- use universal indicator solution and a pH meter to measure pH
- describe acidity, neutrality and alkalinity in terms of the pH scale
- describe the characteristic properties of acids in terms of their reactions with metals, bases and carbonates that are found in daily lives: — metals (e.g. cooking utensil)
- describe the characteristic properties of acids in terms of their reactions with metals, bases and carbonates that are found in daily lives: — bases (e.g. toothpaste, antacid)
- describe the characteristic properties of acids in terms of their reactions with metals, bases and carbonates that are found in daily lives: — carbonates (e.g. baking soda, effervescent vitamin C tablet) [knowledge of general products is required; chemical names of salts and equations are not required]
- state that neutralisation takes place when an acid reacts with a base and the products can be salt and water only
Lessons
Work through them in order.
- Measuring liquid and solid volumeRead a measuring cylinder at the meniscus and find the volume of an irregular solid by displacement.
- Recovering solids and liquids from mixturesUse dissolving, filtration, evaporation and distillation to collect the required solids or liquids.
- Paper chromatography of food dyesRun a valid paper chromatogram and compare separated food dyes with known samples under the same conditions.
- Chemical changes and ways to slow themDistinguish chemical reactions from physical changes, and explain how to slow decay, fuel-fired cooking, burning and rusting.
- Indicators and pHTest solutions with litmus, universal indicator and a pH meter, and classify them as acidic, neutral or alkaline.
- Acid reactions and neutralisationPredict products from the other reactant, identify gases with evidence, and distinguish neutralisation from the final pH.
Practise and check
Or choose
Topic reference
Quick reference
| To | Use |
|---|---|
| measure a liquid’s volume | measuring cylinder, read at eye level |
| separate an insoluble solid | filtration |
| get a dissolved solid back | evaporation |
| collect the liquid from a solution | distillation |
| separate dyes | paper chromatography |
| tell acid from alkali | litmus |
| measure pH | universal indicator or a pH meter |
| Acid reacts with | Products |
|---|---|
| a metal | salt + hydrogen |
| a metal oxide or hydroxide | salt + water |
| a carbonate | salt + water + carbon dioxide |
Core knowledge to remember
- A chemical change forms a new substance; a physical change does not.
- A dissolved substance is still there and can be recovered by evaporation.
- Acids have a pH below 7, neutral solutions pH 7, and alkaline solutions above 7.
- Neutralisation is the reaction of an acid with a base.
Common mistakes
- Trying to filter out a dissolved solid.
- Reading the top of a meniscus, or reading at an angle.
- Saying litmus gives a pH number.
- Saying an acid and a metal give carbon dioxide.