Indicators Topic 9 – On the Menu!

Characteristic Chemical Properties A chemical property describes what happens when two substances react with one another. Example: The reaction between a metal and an acid  bubbles (gas) are produced. If a glowing splint is put into a test tube with oxygen gas, it will reignite. If a burning splint is put into a test tube with hydrogen gas, it will pop (small explosion).

Indicators An indicator is a substance that will react when put into contact with a specific substance. Indicators usually demonstrate a colour change when a chemical reaction with a substance has occurred.

Common indicators Here is a list of some indicators you may see in a lab: Blue litmus paper – turns pink in the presence of an acid. Red litmus paper – turns blue in the presence of a base. Phenolphthalein – a clear solution that turns pink in the presence of a base. Universal indicator paper – can be used to determine the pH of a substance when comparing the paper with a colour chart. Cobalt chloride test paper – the paper turns pink in the presence of water (or if a substance contains water). Lime water – a clear liquid that will become cloudy in the presence of carbon dioxide. Sudan III – turns red in the presence of fats. Fehling’s solution – a purple solution that when brought to a boil will turn orange in the presence of carbohydrates. Biuret – a blue solution that turns purple in the presence of proteins. Lugol’s solution – the solution will be yellowish-orange when there is no cornstarch present and will turn a dark purple in the presence of cornstarch