Edta

Question 1

What is a ligand

Answer 1

Latin “to bind”

A molecule or ion that has at least one pair of electrons the can be donated

Lewis base

Question 2

What is a coordination number

Answer 2

The number of ligands bound to the Lewis acid

Question 3

What is mono bi tri dentate ligands

Answer 3

One atom of the ligand bonded to the Lewis acid
2 ligands
Three

Question 4

What is the chelate effect
What is an example of a chealating agent

Answer 4

Acid bound to mores ring ligands

Give the compound enhanced stability

EDTA

Question 5

What is the fully protonated of EDTA
What is the neutral form
What is the most important form

Answer 5

H6Y(2+)
H4Y
Y(4-)

Question 6

When does the Y(4-) form of EDTA dominate

Answer 6

After ph 10.5

At high ph

Question 7

What does the fully deprotonated from (Y4-) of edta bind with

Answer 7

Forms 1:1 complexes with most metal ions

Question 8

What is the effective concentration of edta given by

Answer 8

It’s fraction (*Y4-) that is fully deprotonated

Question 9

What does edta not bind

Answer 9

K+ Na Li

Question 10

The indicator in an edta titration

Answer 10

Binds less strongly to the metal than the edta

Question 11

What is the concentration of [y4-] dependent on

Answer 11

pH it’s crucial to buffer to a basic ph

Question 12

What are the zones of the edta titration curve

Answer 12

1. Before EP the [metal] is determined by excess unreactes metal in solution
2. At EP equal amount of EDTA and metal, [mwtal] is found by dissociation of product and conditional formation constant
3. After ep excess EDTA, use excess [EDTA] in k’f expression to calc [metal]

Question 13

What happens to the endpoint if the k’f is larger
What happens if the pH is lowered

Answer 13

The endpoint is more distinct
Ve point becomes less distinct, k’f lowers, endpoint less sharp

Question 14

What is an auxiliary complexing agent

Answer 14

A ligand that binds to the metal string enough to prevent metalOH from being formed

This is because at high ph metals try forming product with OH which prevent titration with EDTA

Question 15

What does the presence of auxiliary complexing agents do

Answer 15

Lowers amount of free metal
Decreases sharpness of endpoint
Does not change the ep

Question 16

What are metal ion indicators

Answer 16

Have a diff colour when bound to a metal
Must bind to metal less less strongly then edta
Also acid base indicator so need to control ph
Can only be use in certain ph ranges

Question 17

What is meant by indicator blockage
How do we fix it

Answer 17

Metal doesn’t diss isolate from and indicator, so the metal blocks the indicator

Do a back titration:
Add excess EDTA to the analyte
Add the indicator
Titrate excess edta with another standard solution that has another metal

Question 18

Why are back titrations necessary

Answer 18

If the analyte precitptates with out edta present
Analyte reacts too slowly with edta
Analyte block the indicator
The metal ion for the back titration shouldn’t displace analyte from edta

Question 19

What are displacement titrations

Answer 19

Metal displacement
The solution with the analyte metal is titrated with excess EDTA which is complexed to the other metal

Question 20

What is an indirect titration

Answer 20

Used to determine anion concentrations

Anion is precipitated with excess metal ion (concentration known)
The precipitate is filtered then washed
The excess metal in the filtrate is titrated with standard EDTA

Question 21

What is meant by hardness

Answer 21

The total concentration of alkaline earth ions in water (mainly ca and mg)