Question

100 mL of a water sample consumed 10 mL of N/50 H

2

SO

4

during titration using

phenolphthalein as

an

indicator. Few drops of methyl orange were added to the same

solution and titration was continued. The yellow colour of the solution just turned orange

after addition of another 21 mL of the same acid solution. Ca

lculate the type and extent

of alkalinity present in the water sample.

What could be the disadvantages of using this

water sample source in boiler?

Answer 1

Phenolphthalein alkalinity $=\frac{10×\frac{1}{50}×50000}{100}=100ppm$

Methylorange alkalinity $=\frac{21×\frac{1}{50}×50000}{100}=210ppm$

The alkalinity is due to CO$_3^{2-}$ and HCO$_3^-$

HCO₃^- alkalinity $=210-100$

$=110ppm$

CO₃^2- alkalinity $=100×2$

$=200ppm$

Disadvantage

The water will form Calcium and Magnesium Carbonate in boilers.

Solid Carbonate is a bad conductor of heat, hence more electricity or fuel is needed to heat the water.

Thus wastes energy.