Beers Lamburt Law

Question 1

What is spectrophotometry?

Answer 1

Use of a spectrophotometer to quantitatively measure the reflection or transmission properties of a material as a function of wavelength

Question 2

What is spectrophotometer ?

Answer 2

A spectrophotometer consists of both:

Spectrometer: produces light of any selected colour(wavelength)

Photometer: measures light intensity

Question 3

What is the 1st principle of spectrophotometry?

Answer 3

The intensity of color is a measure of the amount of a material in solution

Question 4

What is the 2nd principle of spectrophotometer?

Answer 4

Every substance absorbs or transmits certain wavelengths of radiant energy but not other wavelengths

For ex: chlorophyll always absorbs red and violet light, while it transmits yellow, green, and blue wavelengths. The transmitted and reflected wavelengths appear green- the colour your eye “sees”

Question 5

What happens when light falls on a substance?

Answer 5

• The light can be reflected
• it can be absorbed by the substance
• Certain wavelengths can be absorbed and the remainder transmitted or reflected

Question 6

What is transmittance?

Answer 6

The ratio of the intensity of light transmitted to the intensity of the incident light (I.e. light that initially fell on the surface)

Question 7

What is absorbance?

Answer 7

The negative log of the transmittance

Question 8

Describe the relationship of absorbance with transmittance, path length and concentration

Answer 8

• Absorbance increases as absorbance increases
• Absorbance increases as path length increases
• Absorbance and transmittance have an inverse relationship

Question 9

What is Lambert’s law?

Answer 9

Describes how intensity changes with distance in an absorbing medium

In a uniform absorbing medium, the intensity f beam of light decreases by the same proportion for equal path lengths traveled.

 -The distance travelled through the medium is called the path length

Question 10

What is the extinction coefficient ?

Answer 10

Molar absorbitivity is the measurement of how strongly a chemical species absorbs light at a given wavelength

Question 11

What is the formulas of lambert law?

Answer 11

-log T= -log I/I0 = E is inversely proportional d

D= path length of the cell

Extinction coefficient or absorbance

Question 12

What is Beer law?

Answer 12

The intensity of a ray of monochromatic light decreases exponentially as the concentration of the absorbing medium increases

  - the more dissolved substance you have in a solution, the more light that will be absorbed, and the less tight that will be transmitted through the solution

Question 13

What is the formula of Beer’s law?

Answer 13

-log T= -logI/Io = E is inversely proportional to C

E= extinction coefficient or absorbance

Io= intensity of monochromatic incident light

I= intensity of transmitted

C= concentration of absorbing substance in solution or gas

Question 14

What are the formulas of Beer Lambert law?

Answer 14

E= -logIo. Is inversely proportional to c x d

Absorbance = kid ( A= Exlxc)

K= proportionally constant = molar extinction coefficient

c= concentration of absorbing medium

d or l= path length or thickness of medium

Hence absorbance depends on c and d, the wavelength of the light as well as the nature of substance

Question 15

What is E(curvy E) in Beer lambert law?

Answer 15

E is the proportionality constant, is called the molar extinction coefficient or molar absorptivity. It is a constant for aa given substance, provided the temperature and wavelength are constant. It has units of liter/mol x cm

Question 16

Describe A in beer lambert law

Answer 16

Aa is a dimensionless number

Question 17

State the definition of beer lambert law

Answer 17

The quantitative measurement of light absorption as a function of wavelength can establish both the identity and concentration of a substance in solution

Question 18

What are the units of l and cm in beer lambert law?

Answer 18

l and cm have the usual (cm) and concentration (mol/liter)