Question

100ml of a sample of water require 1 ml of 0.01 M EDTA for titration using EBT indicator. In another experiment, 100 ml of same water sample was boiled, cooled and filtered and this on titration required 8 ml of EDTA. Calculate the total, temporary and permanent hardness.

Answer 1

Given:

In the titration of standard EDTA vs water sample.

the volume of water sample taken = 100ml

the volume of EDTA solution consumed = 1ml

In the titration of standard EDTA vs boiled water sample.

the volume of boiled water sample taken = 100ml

the volume of EDTA solution consumed = 8ml

To Find:

Calculate the total, temporary and permanent hardness.

Solution:

Calculation of total hardness,

the volume of water sample taken = 100ml

the volume of EDTA solution consumed = 1ml

Total hardness = $\dfrac{volume of EDTA \times 1000}{volume of water sample}$

$= \dfrac{1 \times 1000}{100}$

= 10 ppm

Calculation of permanent hardness,

the volume of boiled water sample taken = 100ml

the volume of EDTA solution consumed = 8ml

$permanent hardenss = \dfrac{volume of EDTA \times 1000}{volume of water sample}$

$= \dfrac{8 \times 1000}{100}$

= 80 ppm

Calculation of temporary hardness,

Temporary hardness = total hardness - permanent hardness

                                   =  10 - 80 ppm = -70 ppm

that is not possible hardness can't be negative thus, there should be an error in readings.