Spectrophotometer

Question 1

What does monochromator do?

Answer 1

Splits light into different wavelengths + colours

It can be diffraction grating or a prism

Question 2

What does slit do ?

Answer 2

Can select wavelength

Question 3

Give examples of light sources

Answer 3

Tungsten bulb
Halogen lamp
Mercury vapour

Question 4

What is the detector used?

Answer 4

Photodiode

Question 5

What is equation for transmittance ?

Answer 5

Is defined as T=I/I0
I0= intensity of incident light
I= intensity of transmitted light

I0= I zero

Question 6

What is equation for absorbance?

Answer 6

A=log10 (I0/I)

Therefore A= log10 (T)

Question 7

Why is absorbance used rather than transmittance?

Answer 7

Absorbance is additive + linear relationship to concentration

Question 8

What does absorbance of sample depend on?

Answer 8

Depends on wavelength

Question 9

What is equation of Beer Lambert law?

What is molar extinction coefficient?

Answer 9

A= e x l x c
L= path length in cm
e (epsilon)= extinction coefficient
C= concentration

Absorbance is proportional to path length
MEC( molar extinction coefficient)= is theoretical absorbance of 1cm of one molar solution => units: M^-1 cm^-1

Question 10

What are some practical applications?

Answer 10

Solution must be homogenous
Solution must be clear - no turbidity
Need to use blank cuvette with solvent => to allow for any absorbance of cuvette
Need to zero using blank after changing wavelength
Because output of light source + sensitivity of detector vary with wavelength