post lab discussion: exp. 8

Question 1

Titration involving the complexation of a chelating agent with a metal.

Answer 1

Complexometric titration

Question 2

Compound which provides more than one pair of electrons for complexation (example)

Answer 2

chelating agent (EDTA-ethylenediamine tetraacetic acid)

Question 3

EDTA

Answer 3

It is a polyprotic acid
4 carboxylic acid
2 amine groups with lone pair electrons

Question 4

refers to amount of Ca and Mg ions in the water sample

Answer 4

Water hardness

Question 5

Why are high concentrations of Ca and Mg ions are undesirable

Answer 5

Due to the formation of insoluble carbonate deposits and formation of soap scum

Question 6

How can water hardness be determined

Answer 6

Titration with a standard EDTA solution
At pH 10 - so that edta will maintain its diabetic form and prevent precipitation of Mg(OH)2

Question 7

What is the mole ration when H2EDTA2- forms a complex with Ca2+ and Mg2+

Answer 7

1:1

Question 8

EBT indicator

Answer 8

Eriochrome Black T
An metallochromic indicator - change their color when combined to metal ions

Question 9

What happens when all of the calcium and magnesium ions have already reacted with EDTA (dibasic form)

Answer 9

the excess EDTA (Y) will react with the
Mg-EBT indicator complex producing a color change

Red to blue

Question 10

Additional of HCI

Answer 10

Dissolve CaCo3

Question 11

Boil of the solution (EDTA standardization)

Answer 11

Remove dissolved CO2

Question 12

Why is there a need to add pH 10 buffer

Answer 12

To prevent precipitation of Mg(OH)2

Question 13

Addition of NaOH

Answer 13

To neutralize HCI

Question 14

What is the purpose of adding magnesium ions to the EDTA solution (titrant)

Answer 14

As calcium ions does not form a stable red complex with the EBT indicator therefore direct titration of Ca2+ by the edta may not cause a sharp color change of EBT indicator