Engineering Chemistry Lab

AIM:

To determine the total, permanent and temporary hardness in the
given water sample by EDTA method. A solution of standard hard water
and EDTA are provided.


PRINCIPLE:

EDTA is ethylene diamine tetra acetic acid. Since pure EDTA is not
dissolved in water, Disodium salt of EDTA is taken for this experiment. It
is a complexing agent.

Actually, hard water contains Ca2+ / Mg2+ ions, during this
experiment. EBT is added to hard water. This will from a weak complex
and the reaction is as follows.
[Ca2+ / Mg2+] + EBT [Ca2+ / Mg2+ - EBT] complex
Hard water Indicator Wine - red Colour (weak)
When EDTA is added to this hard water (Complex), EBT is replaced
by EDTA and a stable metal ion with EDTA complex is formed.
[Ca2+ / Mg2+ - EBT] complex + EDTA
[Ca2+ / Mg2+ - EDTA] Complex + EBT]
wine red colour steel blue colour.

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