Color Change of Indicator in Acidic and Basic Solutions
Aim / Objective:
To observe the color of different indicators in acidic and alkaline solutions
Indicators are organic compounds whose color depends on the concentration of hydronium ions (H3O+ or H+). Indicators are used to identify acidic and basic substances as well as be used to approximate the pH of a given solution.
The color of an indicator changes over a pH range of 0-14. pH can also be approximated by using pH paper which is paper impregnated with a variety of indicators which color over a wide range of pH values. The pH value is determined by spotting a drop of the solution on the pH paper and comparing the color produced with those on a chart of colors and pH ranges.
The table below shows some common indicators, their pH ranges and the expected results when added to an acid or base:
Spot-plate, pipet, blue litmus paper, red litmus paper, universal indicator, distilled water, dilute sulphuric acid, dilute hydrochloric acid, ethanoic acid, sodium hydroxide, aqueous ammonia solution, aqueous calcium hydroxide, universal indicator, phenolphthalein, methyl orange. Test-tubes, test-tube rack
Method / Procedure:
- Dry and label seven test-tubes. Add 1cm3 of each solution to the corresponding test-tube.
- Using a pipet add 3-4 drops of one solution to the separate wells of the spot plate.
- Dip the paper indicator into the solution and record your observation on the data table.
- For the liquid indicators use about 2 drops, then record the data.
- Rinse out and dry the spot plate.
- Repeat steps 1 –4 for each solution.
- Tabulate your results