An indicator is a halochromic chemical compound that is added to a solution to determine its pH. It is a chemical detector for hydronium ions. The indicator changes colour to show the pH of the solution. Some indicates are not very precise and only tell us whether the solution is acidic or basic. When the indicator is added to the solution, they bind to hydrogen or hydroxide ions. The different electron configurations of the bound indicator cause the indicator's colour to change.
Some common indicators are: universal indicator, phenolphthalein, methyl orange, litmus, bromothymol blue.
However, there are some indicators that are found in nature in the form of plant pigments known as anthocyanins, which change colour over different pH ranges, depending on source. For example red cabbage juice will change colour to indicate pH if the solution is within the range of pH 1 - pH 12. Red beet juice will change from red to yellow between pH of 11 and 12.
Therefore they are not as reliable as common laboratory indicators. Some other natural indicators include: Carrots, cherries, grapes, hydrangea, onions, poppy petals, rhubarbs, thyme and tulip petals.
To investigate the uses of various common and natural indicators in acidic, neutral and basic solutions.
Part A: COMMON INDICATORS
0.1 M solutions of sodium hydroxide and hydrochloric acid, distilled water, 3 test tubes, test-tube rack, 3 x 100mL beakers, liquid litmus, universal indicator, methyl orange,
1.Using beakers, pour 2cm of acid into one test tube, 2cm of sodium hydroxide into another test tube, and 2cm of distilled water into the third test tube.
2.Add 3 drops of red litmus to each tube. Record results.
3.Repeat steps 2 and 3 for other indicators.
Colour in strong acid (hydrochloric acid)Colour in strong base...