Salts

Salts can be prepared by different methods depending on whether the salt is soluble or insoluble in water. Below are the common methods used:

1. Direct combination of elements

This method involves a direct reaction between a metal and a non-metal to form a salt.

• Example:

$\text{Mg} + \text{Cl}_2 \rightarrow \text{MgCl}_2$

Used mainly for preparing salts of reactive metals with halogens (group 7 elements).

2. Reaction of metals with dilute acids

A metal reacts with a dilute acid to form a salt and hydrogen gas.

• Example:

$\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2$

Applicable for metals above hydrogen in the reactivity series (e.g., Mg, Zn, Fe). Do not use sodium or potassium, as they are too reactive.

3. Reaction of carbonates or oxides with dilute acids

Metal oxides or metal carbonates react with acids to produce salts and other products like water and carbon dioxide.

• Oxide Example:

$\text{CuO} + 2\text{HCl} \rightarrow \text{CuCl}_2 + \text{H}_2\text{O}$

• Carbonate Example:

$\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2$

A clean method for making salts without needing a reactive metal.

4. Crystallization (for soluble salts)

This is a method used to purify and isolate soluble salts after reaction.

Steps:

1. Prepare the salt solution using one of the above reactions.
2. Filter to remove any excess solid.
3. Heat the filtrate to evaporate some water.
4. Allow the solution to cool and crystals to form.
5. Filter and dry the crystals.

• Example: Preparation of zinc sulfate:

$\text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2$

5. Ionic precipitation (for insoluble salts)

Mixing two soluble salts can produce an insoluble salt as a precipitate.

• Example:

$\text{BaCl}_2 + \text{Na}_2\text{SO}_4 \rightarrow \text{BaSO}_4 \downarrow + 2\text{NaCl}$

The insoluble salt (BaSO₄) is formed as a precipitate, which is then filtered, washed, and dried.

Salts have different properties depending on their composition and nature:

1. Color: Some salts are colored (e.g., Iron (II) salts are green, Nickel (II) salts are green)
2. Hydrolysis: Salts can undergo hydrolysis to give acidic or alkaline solutions depending on whether they are made from strong or weak acids and bases.
3. Exposure to Air: Some salts absorb moisture (hygroscopic) or form a solution (deliquescent).
4. Heat Effects: Salts decompose or lose water when heated (e.g., Iron sulfate decomposes to $\mathrm{Fe}_2\mathrm{O}_3$).

Salts have various uses in daily life, including in food, agriculture, water conditioning, and industrial applications:

1. Food: Sodium chloride is used as a seasoning, and sodium bicarbonate is used in baking.
2. Agriculture: Ammonium sulfate and sodium nitrate are used as fertilizers.
3. Water Conditioning: Sodium chloride and sodium carbonate are used to soften water.
4. Highway Deicing: Sodium chloride is spread on roads to prevent freezing.
5. Industrial Uses: Potassium iodide is added to salt to prevent iodine deficiency, and sodium carbonate is used in glassmaking.