Endothermic and Exothermic reactions
ENDOthermic- when the reaction takes in heat energy from its surroundings, E.g: thermal decomposition, (which requires A LOT of heat energy to take place)
EXOthermic- When the reaction transfers the heat energy to its surroundings, E.g. Neutralization reaction- (Acid + Alkali)
An example of a reversible endo/exothermic reaction is:
Hydrated copper sulfate <---> Anhydrous copper sulfate + water
USES of EXO/ENDOTHERMIC REACTIONS:
EXO- Hand warmer: contain chemicals which have a reversible reaction which makes them REUSABLE.
ENDO- COLD PACK- contains ammonium nitrate and water- used to treat sports injuries.
Making soluble salts
Acid + metal --> salt + Hydrogen
Acid + insoluble base --> SALT + Water
Acid + alkali --> SALT + Water
ACID + INSOLUBLE BASE
Copper oxide + sulphuric acid --> Copper sulphate
1. Add copper oxide to sulphuric acid
2. Warm mixture until no more reactions are occuring ( when left over copper oxide is at the bottom, no more reactions occur).
3. Filter solution
4. Add copper sulphate solution to an evaporating dish
- Heat water in a beaker underneath and evaporate about half
5. Leave the solution by window for few days
6. Collect copper sulphate crystals.
Acid + Alkali
Obtainin salt from acid + alkali:
1. Conical flask containing 'X' amount of alkali and Universal Indicator
2. Add acid until solution is GREEN. (Neutral, pH 7)
3. Measure exact amount of acid added.
4. Record measurements
5. Repeat experiment with known amounts of alkali and acid without universal indicator
6. Place solution into evaporating dish
7. Heat water underneath evaporating dish to evaporate some of the solution.
8. Take evaporating dish and put solution near a window for few days
9. Collect salt crystals.
Two aqueuous subtances can react to create a SOLID substance - THIS IS A PRECIPITATION REACTION. Product formed is a PRECIPITATE. (The ions in the solution react)
Lead nitrate + Potassium iodide --> lead iodide - Here the lead ions react with the iodide ions to produce lead iodide.
INDUSTRIAL PROCESS =
1. carry out precipitation reaction,
2. filter it,
3. Dry the precipitate.
USES OF PRECIPITATION REACTIONS:
- Treating effluent: Removing harmful ions from effluent e.g. LEAD, MAGNESE AND CHROMIUM IONS.
E.g. Chromium ions + hydroxide ions --> chromium hydroxide
PREDICTING WHICH SALT IS GOING TO BE MADE
Hydrochloric acid makes CHLORIDES
Sulphuric acid makes SULPHATES
Nitric acid makes NITRATES.
ACIDS AND BASES
Acids contains HYDROGEN IONS H+ (Aq)
Bases refer to metal hydroxides or metal oxides- (a soluble base is called an alkali- ALKALIS CONTAIN HYDROXIDE IONS = OH- (Aq)
HYDROXIDE IONS + HYDROGEN IONS --> WATER
OH- + H+ --> H20
Ammonia + Water --> Ammonium hydroxide (ALKALI)
Example of neutralisation reaction:
Ammonium hydroxide + nitric acid --> ammonium nitrate + water (we must then evaporate and crystalise ammonium nitrate).
Uses of AMMONIUM NITRATE:
- FERTILISER- (contains nitrogen which is required for growth for to make amino acids for protein).