Strength of acid.
The strength of an acid depends on its degree of dissociation / ionisation in water to form hydrogen ions.
Properties of ACID:
- 1. sour taste.
- 2. change the colour of indicators (e.g. turn blue litmus paper red).
- 3. contain hydrogen ions and conduct electricity.
- 4. react with metals, carbonates and bases.
STRONG ACIDS
Hydrochloric acid -> Hydrogen chloride -> HClNitric acid -> Hydrogen nitrate -> HNO3Sulfuric acid -> Hydrogen sulfate -> H2SO4
WEAK ACIDS
Ethanoic acid -> Vinegar
Citric acid -> Lemon
Tartaric acid -> Grape
Reaction with METAL:
Acid + metal → salt + hydrogen
(a) Effervescence observed. Colourless, odourless gas evolved which extinguished a lighted wooden splint with a ‘pop’ sound.
(b) Grey solid reduced in size (when in excess). Grey solid dissolves to form a colourless solution
(c) Heat liberated.
| Potassium | Most Reactive |
| Sodium | |
| Calcium | |
| Magnesium | |
| Aluminium | |
| Zinc | |
| Iron | |
| Tin | |
| Lead | |
| Hydrogen | |
| Copper | |
| Silver | |
| Gold | Least reactive |
*Metals less reactive than HYDROGEN isn't able to react with acid.
Reaction with CARBONATE:
Acid + carbonate → salt + carbon dioxide + water
(a) Effervescence occurs. Colourless, odourless gas evolved which reacts with calcium hydroxide to form a white precipitate.
(b) White solid dissolves to form a colourless solution.
Reaction with BASES:
Acid + base → salt + water
PH LEVELS
| Observation(s) | Indicators | |
| Litmus paper | 1. | An acid turns blue litmus paper red. |
| Methyl Orange | 2. | Used to identify strong acids. Colour change at pH 4 Strong acid turns methyl orange red. Alkali turn methyl orange yellow. |
| Phenolphthalein | 3. | Used to identify strong alkalis. Colour change at pH 9 Strong alkali turns phenolphthalein pink. Phenolphthalein remains colourless in acid. |
| Universal Indicator | 4. | In neutral solutions, universal indicator remains green. Strong acid: red Strong alkali: violet |
No comments:
Post a Comment