When looking at making salts, it is important to remember the neutralisation reaction:
Acid + Alkali → Salt + Water
For example, consider the reaction between hydrochloric acid and sodium hydroxide:
Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water
Here are two more examples:
Another general equation for neutralisation is:
Acid + Base → Salt + Water
Remember, alkalis are simply bases that dissolve in water.
The difference with this equation is that it takes into account the bases that do not dissolve in water, which are called insoluble bases. As insoluble bases do not dissolve in water, they will need to react as solids.
Below are some examples of this reaction:
Both hydrochloric acid (hydrogen chloride) and sodium hydroxide are in aqueous form because they are dissolved in water.
Let’s look at the earlier example to see how we can make and isolate copper chloride.
Hydrochloric acid + Copper oxide → Copper chloride + Water
The symbol equation for this reaction is:
2HCl (aq) + CuO (s) → CuCl2 (aq) + H2O (l)
1. Use a measuring cylinder to measure 30 ml of hydrochloric acid.
2. Pour the hydrochloric acid into a boiling tube and place the tube into a beaker of hot water.
3. Use a spatula to add copper oxide in excess and stir the solution until the hydrochloric acid has stopped reacting.
4. Use filter paper to set up a funnel and place it in a conical flask.
5. Place a gauze pad on a tripod, with an evaporating dish on top of the gauze pad.
6. Once you’ve filtered the solution, pour the filtrate into the evaporating dish.
7. Set up a Bunsen burner under the tripod to gently heat the filtrate in the evaporating dish.
8. Move the evaporating dish to a warm location so that the remaining water can evaporate slowly.
9. The copper chloride produced will crystallise as the filtrate slowly evaporates, leading to the formation of larger salt crystals.
Acid + Metal → Salt + Hydrogen
The formation of copper chloride in this reaction is represented by the equation:
Hydrochloric acid + Copper → Copper chloride + Hydrogen
Acid + Metal carbonate → Salt + Water + Carbon dioxide
You can see how copper chloride is made in this reaction through the equation:
Hydrochloric acid + Copper carbonate → Copper chloride + Water + Carbon dioxide