Environmental Chemistry- Analysis of an Acid Rain Solution:
Purpose: To prepare a standard solution of sodium hydroxide and to use that solution in a titration to analyze a solution of acid rain and to calculate the concentration of the sulfuric acid it contains.
Apparatus:
- 250 ml Erlenmeyer flask
- Electronic Balance
- 100 ml Beaker
- 100 ml Conical Flask
- 10 ml Pipette and Filler
- Burette
- Stirring rod
Materials:
- Solution of Acid Rain
- Sodium hydroxide solution (0.5 mol dm-3)
- Distilled Water
- Phenolphthalein Indicator
Procedure:
- Use a pipette and pipette filler to transfer 25 ml of the ‘acid rain’ sample to a 100 ml conical flask. Add 5 drops of phenolphthalein indicator.
- Fill a burette with 0.5mol dm-3 sodium hydroxide solution. Make sure that the burette jet is full of solution.
- Add sodium hydroxide solution, in small volumes, to the ‘acid rain’ solution in the conical flask. Swirl the flask after each addition.
- Phenolphthalein indicator is colorless in acidic solution but pink in alkaline solution. Run in the small volumes of sodium hydroxide solution until you first observe a permanent color change in the titration mixture.
- Your first attempt will be a rough titration; you will have gone beyond the end-point and added more sodium hydroxide than is needed to react with all the acid in the flask. You should, however, now have an idea of what the end-point is. Do several more titrations until you record two volumes that agree within 0.1 ml. When you get near the end-points of these titrations, you should add the sodium hydroxide carefully, adding only one drop of solution at a time until new permanent color is produced.