Lesson summary
6.1 Acids and Alkalis — CHECKPOINT (CHEMISTRY) notes: Describe acids, alkalis, indicators, the pH scale and neutralisation.Acids in food — fruits such as lemons and limes contain citric acid, a weak acid with a sour tasteLaboratory acids — hydrochloric acid, sulfuric acid and nit…
- Strong acids
- Dilute acids
- Alkalis in products
- Laboratory alkalis
- Strong alkalis
- Safety glasses
Section 1 of 8Acids
- Acids in food
- fruits such as lemons and limes contain citric acid, a weak acid with a sour taste
- Laboratory acids
- hydrochloric acid, sulfuric acid and nitric acid
- Strong acids
- are corrosive and dissolve skin, causing chemical burns
- Dilute acids
- are less dangerous but still irritate skin and eyes
- Spills
- wash with lots of water, which dilutes the acid
Section 2 of 8Alkalis
- Alkalis in products
- many cleaning products contain sodium hydroxide, a strong alkali
- Laboratory alkalis
- sodium hydroxide, potassium hydroxide and calcium hydroxide
- Strong alkalis
- are corrosive and make skin feel soapy as they burn it
- Eyes
- alkalis are harmful if they get in the eyes
- Dilution
- dilute alkalis are less dangerous
Section 3 of 8Working safely
- Stand up
- so spills do not fall on you
- Safety glasses
- so nothing enters your eyes
- Bottle top
- place it upside down on the bench so it does not pick up dirt or contaminate the surface
- Replace the top
- as soon as you finish to prevent spills and wrong tops
Section 4 of 8Litmus
| Substance | Litmus colour | Type |
|---|---|---|
| Hydrochloric acid | Red | Acid |
| Lemon juice | Red | Acid |
| Water | Purple | Neutral |
| Sodium hydroxide | Blue | Alkali |
| Calcium hydroxide | Blue | Alkali |
- Litmus
- a common dye, used as litmus paper made by soaking absorbent paper in litmus solution
- Neutral = neither acid nor alkali
Section 5 of 8Universal indicator
| Type of substance | Colour | pH |
|---|---|---|
| Strong acid | Red | 1 |
| Weak acid | Yellow | 4 |
| Neutral | Green | 7 |
| Weak alkali | Blue | 10 |
| Strong alkali | Purple | 13 |
- Universal indicator
- a mixture of indicators that shows how acidic or alkaline a substance is
- Simple indicators
- only show whether a substance is acid or alkali
Section 6 of 8The pH scale
- pH scale
- measures the strength of acids and alkalis from 0 to 14
- Below 7
- acidic; more acidic as the pH gets lower
- pH 7
- neutral
- Above 7
- alkaline; more alkaline as the pH gets higher
- Chemical property
- the pH of a substance is one of its chemical properties
Section 7 of 8Neutralisation
- Neutralisation
- acid + alkali → salt + water, and the pH moves towards 7
- Acid + metal oxide
- → salt + water
- Acid + carbonate
- → salt + water + carbon dioxide; the fizzing is the test
- Examples
- indigestion tablets neutralise stomach acid; lime is added to acidic soil
Section 8 of 8Hazard symbols
| Symbol | Meaning |
|---|---|
| Explosive | Can explode with a flame or heat |
| Flammable | Catches fire easily |
| Oxidising | Gives off a large amount of heat in contact with other substances |
| Corrosive | Destroys living tissue and causes burns |
| Toxic | Can poison you |
| Hazardous to the environment | Can kill or damage living things in the environment |
| Health hazard | Can cause harm such as irritating skin and eyes |
| Serious health hazard | Can cause a serious health problem |
Marked practiceQuizzes for this lesson
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