SS - Transition Metal Ion Colour

Question 1

Give the complementary colours for:

i) Red
ii) Yellow
iii) Green

Answer 1

i) Cyan
ii) Blue
iii) Magenta

Question 2

What colours of light can be inferred to have been absorbed by an object by the colour of the object?

Answer 2

The colours seen are the complements to the colours which are absorbed

Question 3

What 3 factors effect the colour absorbed by transition metals?

Answer 3

1) The oxidation state of the ion
2) The type of ligand
3) The coordination number/shape of the complex

Question 4

What can be used to measure the absorbance of a solution?

Answer 4

A Colorimeter

Question 5

Describe how you would use a colorimeter to measure the absorbance of a solution

Answer 5

1) Use a filter that produces a colour which is absorbed by the transition metal you are looking at, otherwise it won’t be absorbed and there will be no change
2) Zero the colorimeter by measuring the absorbance of a blank sample - a sample of the solvent your metal ions are dissolved in
3) The monochromatic light from the filter travels through the sample, where some is absorbed. The remaining light reaches the detector which compares the absorbance of the sample to the zero point

Question 6

What does a high absorbance reading show about the sample in a colorimeter?

Answer 6

A lot of the light has been absorbed so the sample is very concentrated

Question 7

What are samples in a colorimeter placed in?

Answer 7

A cuvette

Question 8

How would you find the concentration of unknown metal solution using colorimetry?

Answer 8

By comparing the absorbance to a calibration graph for that transition metal

Question 9

Describe how a calibration graph is made

Answer 9

By measuring the absorbance of samples with a known concentration
These standard samples can be made by dissolving different amounts of the metal ion in a fixed volume of water OR by making consecutive dilutions of a single concentrated solution