Before we continue lets define a few terms.

The term pH is used to describe how acidic or basic a solution is. It ranges from values between 1 (very acidic) to 14 (very basic).

An acidic solution has a high concentration of H⁺ ions and a low concentration of OH^- ions.

A basic solution has a low concentration of H⁺ ions and a high concentration of OH^- ions.

An acid is a chemical that increases the concentration of H⁺ ions in water.

A base is a chemical that increases the OH^- ions in water.

A neutral solution has a pH of 7 and is one that contains equal amounts of OH^- ions and H⁺ ions

Universal indicator is a mixture of different chemicals that change colour over a range of pH values.

Neutral solutions are green while acidic solutions are red. Basic solutions appear blue. This is the chemistry behind some very impressive colour magic.

Adding chemicals such as acids and bases to a solution with universal indicator can be quiet spectacular, if done by a competent person. The image on the right shows the vivid colour change. The solution starts with blue indicating a solution that is low in H⁺ but high in OH^-. After the addition of an acid the solution changes through different colour transitions to a red colour indicating a high concentration of H⁺ and low concentration of OH^-.

A measuring cylinder with a solution containing universal indicator can be the start of very interesting displays. Note the image on the right. The cylinder contains a blue solution, indicating a base is added to the water. Then some dry ice (carbon dioxide) is dropped into the measuring cylinder creating a very impressive display of colour and smoke.

Carbon dioxide when dissolved in water forms an acidic solution. As the H⁺ concentration increases and the OH^- concentration decreases the colour of the solution changes from blue to red.

1) Universal indicator is added to a solution and the colour changes from clear to green This means that the pH of the solution is around 7 the solution is very basic the solution is very acidic

2) A solution containing universal indicator is blue in colour. A clear liquid is added that changes the solution to a deep red colour. This clear liquid is most likely water an acid a base neutral (neither an acid nor a base)

3) How do we know that carbon dioxide when dissolved in water turns the water acidic. The solution will turn the universal indicator deep blue The solution will turn the universal indicator green The solution will turn the universal indicator light orange.

4) Universal indicator is placed in a clear solution and quickly changes the colour to a deep blue. This indicates equal amounts of H ions and OH ions a high H ion concentration a high concentration of OH ions

5) Vinegar is the commercial name for acetic acid. What do you think vinegar will do when placed in water? give hydrogen ions to water take hydrogen ions from water nothing, because vinegar is not a strong base

6) Baking powder when placed in water takes hydrogens from water molecules to form OH^- ions. A solution of baking powder will turn universal indicator red green blue