ESTIMATION OF THE TOTAL HARDNESS IN A WATER SAMPLE USING EDTA Flashcards
what do you titrate water against to find the hardness
EDTA
what does EDTA stand for
ethylenediaminetetraacetic acid
what do you use during the titration
the disodium salt of the acid
how do you represent the disodium salt of the acid
Na2H2X
formula for experiemny
Na2H2X + Ca2+ -> CaH2X + 2Na+
indicator for the titration 2
eriochrome black or solochrome black
what does eriochrome black look like
a black powder
eriochrome black in hard water
wine/red
eriochrome black in non-hard water
blue
end point colour change
wine/red to blue
as the end point is difficult to detect, what must be done
must be carried out at a particular pH
how do you carry it out at the right pH?
use pH buffer 10
where is EDTA stored and why?
in a plastic containing as it has the ability to extract metal ions from glass if left in a glass container for too long
to make it easier, what do we attribute all hardness to?
CaCO3
first step
burette is washed out with deionised water and then some of the EDTA solution to prevent dilution
after burette cleaned
burette filled using a funnel (usual precautions)
after burette filled
clamped vertically
after burette ready
pipette washed with deionised water and then with water sample to prevent dilution of the sample
pipette washed `
25 cm cubed of hard water sample pipetted into conical flask by touching tip off the inside of the conical flask
water sample in conical flask
added 1cm cubed of buffer solution 10
buffer solution in flask
pinch of Erichrome black added into conical flask also
what colour is solution in conical flask when ready
wine/red
burette and conical flask ready
carry out titration until end point
