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Chemistry Salts Preparation

Here is a concise summary on Chemistry Notes Salts Preparation. Secondary 3 students start learning this topic in the second half of the year. This topic can be quite a killer as there are many information to digest and memorize.

Salts:

In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions (cations) and negatively charged ions (anions).

Water of Crystallisation:
When salts combine with water of crystallisation, they form crystalline solids that can either be hydrated or anhydrous:

  • Hydrated salts: Contain water of crystallisation.
  • Anhydrous salts: Do not contain water of crystallisation. Heating hydrated salts removes the water.

Example:
Hydrated copper sulfate (CuSO₄·5H₂O) is blue.
Anhydrous copper sulfate (CuSO₄) is white.

Before diving into salts preparation, students need to learn about salt solubility.

Watch this clip for 3 tips on learning salts solubility.

You can also find other useful notes on our iG or tiktok handle. 🙂

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Preparation of Salts:

1) Insoluble Salt
Method: Precipitation

NOTE: 2 Aqueous reagents are needed. The reagents used should contain the cation and anion in the salt prepared.

Steps:
Pour aqueous reagent A to aqueous reagent B in beaker with constant stirring. Precipitation occurs.

Filter the mixture to separate the insoluble salt as residue, then wash with distilled water and dry between filter paper.

2) Soluble SPA / Group 1 Salt.
Method: Titration

General Reaction:
Acid + Alkali → Salt + Water
Acid + Soluble Carbonate → Salt + Water + CO₂

Procedure:
Use exact volumes of starting materials to avoid excess, as both reactants are soluble and can contaminate the salt.

Use an indicator to determine the end point.
Steps:

Fill a burette with acid.
Pipette 25.0 cm³ of alkali into a conical flask.
Add 2 drops of a suitable indicator to the flask.
Slowly add acid from the burette until the indicator changes colour with a single drop.
Note the volume of acid used. Repeat the experiment without the indicator and add the recorded volume of acid to the alkali in the beaker.

Pour the solution into an evaporating dish.
Heat the solution until it becomes saturated.
Allow the solution to cool so that crystals can form.
Filter and wash the crystals with distilled water, then dry them between pieces of filter paper.

3) Soluble Non- SPA / Group 1 salts.
Method: Adding Excess & Insoluble Solid to Acid:

General Procedure:

Add an excess of insoluble solid to the acid.
Filter the mixture to remove any excess unreacted solid, collecting the filtrate.
Heat the solution until it becomes saturated.
Allow the solution to cool, so crystals can form.
Filter to collect the crystals, then wash them with distilled water and dry between pieces of filter paper.
Key Points:

Adding excess insoluble solid ensures all the acid has reacted, preventing contamination of the soluble salt by the acid.
Excess insoluble salt can be separated from the soluble salt by filtration.

Very reactive or unreactive metals (Na, K, Ca, Au, Ag, Cu) cannot be used. Suitable metals include Mg, Fe, Zn, and Al.

Look out for Part 2 for free Chemistry Notes Salts preparation! 🙂

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