Preparation of Salts: Basics

• A salt is an ionic compound made up of positively charged ions (cations) and negatively charged ions (anions).
• Salts can be prepared through a few methods, primarily acid-base reactions, precipitation reactions, and direct combination of elements.

Preparation from Acid-Base Reactions

• Most salts are derived from an acid-base reaction, where an acid reacts with a base to form salt and water, a process known as neutralisation.
• The base could be a metal oxide, a metal hydroxide or a metal carbonate. For example, when hydrochloric acid reacts with sodium hydroxide, the resulting salt is sodium chloride.

Preparation from Precipitation Reactions

• Precipitation reactions can be used to prepare insoluble salts. They involve mixing two solutions that each contain one of the ions needed for the salt.
• The resulting product, an insoluble salt, separates as a solid precipitate. For instance, a solution of silver nitrate mixed with a solution of sodium chloride forms an insoluble salt, silver chloride, which forms as a precipitate.

Direct Combination of Elements

• Direct combination of elements, or synthesis, can be used to prepare salts if one of the ions in the salt is derived from an element that reacts with a compound containing the other ion needed for the salt.
• This method generally involves a more vigorous chemical reaction, such as the direct reaction of a metal with a non-metal. For instance, sodium reacts directly with chlorine gas to form sodium chloride.

Crystallising Salts

• After a salt has been formed, it is often necessary to purify it by crystallisation.
• This involves first forming a saturated solution of the salt, then allowing the solution to cool slowly. As it cools, the salt will gradually form crystals that can be collected and dried.

Solvent Considerations

• The choice of solvent can greatly impact the crystallisation process and the type of salt that can be obtained.
• Typically, water is used, but for certain salts that are water-soluble, a different organic solvent may need to be used.

Properties of Salts

• Physical properties of salts include high melting and boiling points, crystal structure, and the ability to conduct electricity when dissolved or melted.
• Salts are typically soluble in water, but insoluble in most organic solvents. However, there are exceptions, like silver chloride, which is insoluble in water.
• Salts exhibit a variety of colours depending on the specific ions present.