Acids, Bases and Salts

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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.

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Making soluble salts

Acid + metal --> salt + Hydrogen

Acid + insoluble base --> SALT + Water

Acid + alkali --> SALT + Water

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ACID + INSOLUBLE BASE

Copper oxide + sulphuric acid --> Copper sulphate

Process:

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.

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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.

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Insoluble salts:

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

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PREDICTING WHICH SALT IS GOING TO BE MADE

Hydrochloric acid makes CHLORIDES

Sulphuric acid makes SULPHATES

Nitric acid makes NITRATES.

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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

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Ammonium salts

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).
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