Past edta Exam Questions Flashcards
What is the full name of the edta reagent?
Ethylenediaminetetraacetic acid
Ethylene Diamine Tetra Acetic Acid
Name an indicator suitable for this titration.
Eriochrome Black T/Solochrome Black
State the colour change observed at the end point of the titration
Wine red to blue
What is the general purpose of buffer solution?
A buffer solution is a solution that resist changes in pH, i.e. it keeps the pH constant
What buffer was required for this titration?
Buffer pH 10
What problem would have been encountered in this titration if the wrong buffer were used?
If the wrong buffer were used you would get an inaccurate end point because there would be incomplete complexing of the edta with calcium and magnesium ions
Explain two operations, involving the titration flask and its contents, carried out as the edta was being added from the burette during the titrations
(3)
The titration flask is swirled to mix the contents
The sides of the flask are washed down with deionised water
The flask is placed on a white tile to help observe the colour change
State and explain whether the water having passed through the deioniser is suitable for use as dionised water in the laboratory or if the deioniser needs to be changed or regenerated
(2)
The water is not suitable for use as deionised water after being passed through the deioniser because the water is still hard, i.e. it still contains Ca2+ and Mg2+ ions
The deioniser needs to be changed because the water is still hard after being passed through the deioniser
Describe the correct procedure for rinsing the burette and filling it with edta reagent
(4/9)
Rinse with deionised water
Rinse with reagent
Clamp vertically
Use funnel when adding reagent
Remove funnel after filling
Open tap to fill below tap
Remove air bubbles
Set bottom of meniscus on mark
Read bottom of meniscus
The addition of a small quantity of another solution to the water in the conical flask is essential before commencing the titration
What solution must be added?
Buffer
Why must a buffer solution be added?
1/2
To keep pH at 10
To ensure accurate end point
A whitisg deposit is often found on the insides of kettles in hard water districts. If some of this deposit is scraped into a test tube and dilute hydrochloric acid is added a reaction is observed.
Write a blanced equation for this reaction
CaCO3 = 2HCl –> CaXl2 + H2O + CO2
Calculate …
What formula would you use to calculate the hardness of water in ppm of CaCO3
Vca x Mca/Nca = Ved x Med/Ned
