Acids, bases and salts
1. WHAT ARE THE CHEMICAL REACTIONS OF ACIDS AND BASES?
Acids and bases differ in the types of reactions they undergo and the products formed. These reactions can be used to distinguish between acids and bases.
2. HOW ARE SALTS FORMED?
Salts are substances which contain a positive ion from a metal (or ammonium ion) and a negative ion from a non-metal. Salts are usually formed when acid reacts with a base or a carbonate or metal. Salts can also be formed when an ammonium salt is heated with an alkali and when two soluble salts are mixed. The methods used to obtain salts include titration, direct combination and precipitation. The type of method chosen depends on the solubility of the salt. Soluble salts dissolve in water (e.g., NaCl, KNO3), while insoluble salts do not dissolve in water (e.g., PbCl2, BaSO4).
A soluble salt is usually prepared by reacting the acid solution with the base, metal or carbonate. The solution is heated to remove excess water, filtered, then a small quantity of the filtrate is left to evaporate.
Crystals formed in this way usually have their water of crystallization and are termed hydrated salts (e.g. CuSO4.5H2O). If they are heated to dryness and all the water of crystallization is removed, the salts become anhydrous.
Hydrated salts usually change colour when the water of crystallization is removed by heating.
Insoluble salts are usually prepared by mixing two solutions of soluble salts together, then filtering, washing and drying the precipitate formed. This is also called a double decomposition reaction.
Example: lead nitrate + sodium chloride = lead chloride + sodium nitrate
The lead chloride formed is the insoluble salt, which would be seen as a precipitate.
Pb (NO3)2 (aq) + 2 NaCl (aq) = PbCl2 (s) + 2 NaNO (aq) 3
3. DIFFERENTIATE BETWEEN AN ACID SALT AND A NORMAL SALT
Salts can also be termed normal or acid salts. If all the hydrogen ions are replaced in the acid, a normal salt is formed. However, if the hydrogen ions were only partially replaced, an acid salt is formed. Acid salts are formed from dibasic and tribasic acids.
Example: H2CO3 - Carbonic acid is dibasic (has 2 hydrogen ions available to be replaced). If carbonic acid reacts with sodium hydroxide, two salts can be formed.
2 NaOH (aq) + H2CO3 (aq) Na2CO3 (aq) + 2 H2O (l) Normal salt, sodium carbonate, is formed.
NaOH (aq) + H2CO3 (aq) NaHCO3 (aq) + H2O (l) Acid salt, sodium hydrogen carbonate or sodium bicarbonate, is formed.
4. HOW ARE SALTS USED IN DAILY LIFE?
Salts are used in a variety of ways, from sweeteners to medicines and additives and preservatives in the food industry.
5. Cite some applications of neutralization reactions in everyday life.
Neutralization reactions refer to reactions involving acids and bases (carbonates, etc).
COMMON EXAMPLES OF NEUTRALIZATION INCLUDE:
1. Adding lime (calcium oxide) to acidic soils to reduce soil acidity.
2. Taking antacids (indigestion tablets) to treat acid indigestion in the stomach.
3. Brushing with toothpaste (basic) to reduce acidity in the mouth.
4. Acid rain damaging carbonate rocks, buildings and metals.
5. Using baking soda (basic) to neutralise a bee sting (acidic).
6. Using vinegar (acidic) to neutralise a wasp sting (basic).
Students from Mount Alvernia High School in Montego Bay, St James, get information on how to apply to Bryant University in Rhode Island, United States, from Claire Dunning (right), senior assistant director, international admissions, Bryant University,...