Environmental Chemistry- Analysis of an Acid Rain Solution:

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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:

  1. 250 ml Erlenmeyer flask
  2. Electronic Balance
  3. 100 ml Beaker
  4. 100 ml Conical Flask
  5. 10 ml Pipette and Filler
  6. Burette
  7. Stirring rod

Materials:

  • Solution of Acid Rain
  • Sodium hydroxide solution (0.5 mol dm-3)
  • Distilled Water
  • Phenolphthalein Indicator

Procedure:

  1. 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.
  2. Fill a burette with 0.5mol dm-3 sodium hydroxide solution. Make sure that the burette jet is full of solution.
  3. Add sodium hydroxide solution, in small volumes, to the ‘acid rain’ solution in the conical flask. Swirl the flask after each addition.
  4. 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.
  5. 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.
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Data Collection & Processing:

        

Sodium Hydroxide + Sulphuric Acid → Sodium Sulphate + Water

2NaOH                   +                  H2SO4           →           Na2SO4        +  2H2O

Average Volume to neutralize Sulphuric Acid:

 = 10.93 cm3

Concentration of NaOH:

= 0.5 mol dm-3

Moles= Concentration x Volume

*Volume must be in dm3

Moles= 0.5 mol dm-3 x

Moles= 0.0055 of NaOH

Ratio between NaOH and H2SO4 is 2:1

Hence, number of moles of H2SO4 is half number of NaOH moles:

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