ENVIRONMENTAL BIOTECHNOLOGY

Experiment 4

Aim of the Experiment : DETERMINATION OF TOTAL ALKALINITY OF WATER

Introduction

Generally, pH of water remains neutral. Alkalinity of water represents the presence of hydroxyl ions (-OH) in water, hence, it is capacity of water to neutralise a strong acid. In natural or wastewater alkalinity is due to the presence of free hydroxyl ions which cause through hydrolysis of salts by weak acids and strong bases (e.g. carbonate and bicarbonates).

Materials required

• • • Conical flask (100 ml capacity)

    • Water sample

    • Titration assembly

    • HCl solution (0.1N)

    • Na,CO, solution (0.1N) (dissolve 5.3 g of Na,CO, in distilled water and dilute to make 1 litre)

    • Phenolphthalein indicator (dissolve 0.5 g of phenolphthalein in 50 ml of 95% ethanol and 50 ml of distilled water. Add 0.05N NaOH solution drop by drop to make solution faintly pink)

    • Methylene orange indicator (dissolve 0.5 g of methylene orange in 100 ml of distilled water)

Procedure:

1. Take 50 ml of water sample in a conical flask (100 ml capacity).

2. Add a few drops of Phenolphthalein indicator. If colour of water does not change, it means

3. that Phenolphthalein alkalinity (PA) is nil due to absence of carbonates in the water sample.

4. Moreover, if there develops pink colour, determine PA.

5. Pour 0.1N HCl solution in burette and titrate with water sample. Note the end point when

6. pink colour becomes colourless.

7. Take another 50 ml of water sample in flask and add 2-3 drops of methyl orange into it.

8. Colour turns to orange.

9.Transfer 0.1N HCl solution into burette in titration assembly and titrate with the water sample

10. (methylene orange added) until yellow colour changes to pink.

11. Note the end point.

Result:

Calculate PA and total alkalinity of water sample as below:

Phenolphthalein indicator (mg/litre) = Volume of 0.1 N HCl solution used as titrant x 1000

Volume of water sample

Methylene orange alkalinity (mg/litre) = Volume of 0.1 N HCl solution used as titrant x 1000

Volume of water sample