1 cup rock salt, or Epsom salts (can be bought from supermarkets or pharmacies), or a mixture of both
1/2 cup citric acid (from the supermarket)
1 cup sodium bicarbonate, often called bicarbonate of soda or baking soda
½ cup olive oil or another vegetable or nut oil good for your skin
Optional: something to colour your bath bombs (food colouring) and something pleasantly smelly (essential oils)
What to do
Mix all the dry ingredients in a bowl
Slowly stir in oil, food colouring and fragrance to mixture. Mix well.
Make into balls in the palm of your hand. If mixture is to dry to do this, you can add a little more oil.
Place bath bombs on a greaseproof sheet to dry. The balls will become semi-hard to hard within 2-3 hours, but let them sit there a day or two for them to fully dry before storing.
Store bath bombs in a sealed container, away from moisture.
When you are ready to have a soak, drop one into the bath and watch it fizz as the sodium bicarbonate and citric acid react together in the water.
Enjoy a soak in the salts.
What's happening?
While you are having a dip, you can contemplate chemistry. You have just added an acid and a base to water and are now blissfully lying in the salty results.
The humble, 'under the kitchen sink' sodium bicarbonate has hundreds of uses and is a hot bed of interesting chemistry. Sodium bicarbonate is a base and when it reacts with an acid, a chemical reaction occurs.
Both lemons and vinegar are acids and you can taste their sourness on your tongue. Bases are the opposite of acids; they normally taste bitter and feel soapy.
Being an acid and a base has some strict guidelines - bases accept hydrogen ions, H+, and acids donate them.
This is called the proton theory of acids and bases, introduced independently in 1923 by the Danish chemist Johannes Nicolaus Brønsted and the English chemist Thomas Martin Lowry, stating that any compound that can transfer a proton to any other compound is an acid, and the compound that accepts the proton is a base.
A proton is a nuclear particle with a unit positive electrical charge; it is represented by the symbol H+ because it constitutes the nucleus of a hydrogen atom.
Acids and bases need each other. According to the Brønsted-Lowry scheme something can function as an acid only in the presence of a base; and a substance can function as a base only in the presence of an acid.
The citric acid (acid) reacts with the sodium bicarbonate (base) to form carbon dioxide gas. The reaction between citric acid and sodium bicarbonate in your bath tub looks like this:
[citric acid, sodium bicarbonate and water become water, carbon dioxide and products, salts]
Whenever an acid and a base neutralise each other, the products of the reaction always include a salt.
What's a salt? A salt is a compound that consists of cations (positive ions) and anions (negative ions). An ion is an atom, or a group of atoms with a net electric charge. The simplest of all ions is the electron with a negative charge, and the proton with a positive charge.
Salts are everywhere, the most common being sodium chloride, the type that is good on chips (NaCl). Nearly all salts dissolve to a certain extent in water.
Applications
We salute sodium bicarbonate and all its uses! Here are just a few:
Sodium bicarbonate is used to absorb moisture and odours, an open box can be left in a refrigerator for this purpose.
A paste from sodium bicarbonate can be very effective when used in cleaning and scrubbing. Used in toothpaste, sodium bicarbonate helps to gently remove stains, whiten teeth, freshen breath, and dissolve plaque.
Sodium bicarbonate is used as a fire-suppression agent in some dry powder fire extinguishers.
