SpectrophotometrySpectrophotometrySpectrophotometrySpectrophotometry

SpectrophotometrySpectrophotometry• Terms and definitions………

1.Electromagnetic radiation• You actually know more about it

than you may think!

Electromagnetic radiation

• The electromagnetic (EM) spectrum is just a name that

scientists give a bunch of types of radiation when they want to talk

about them as a group.

Electromagnetic radiation

• Examples of groups or radiation:

• visible light that comes from a lamp in your house

• radio waves that come from a radio station are two types of electromagnetic radiation.

Electromagnetic radiation

• EM travels through space in the form of a wave

• Wavelength– Short ( high energy) nuclear power– Long (low energy) am radio

Electromagnetic radiation

• Light occupies a small portion of this spectrum.– Visible spectrum –we see these colors

Think about it…• Each color in a rainbow

corresponds to a different wavelength of electromagnetic spectrum

Electromagnetic radiation

• Color?

• Substances process color because of their ability to absorb and transmit certain wavelengths of visible light.

Electromagnetic radiation

• Examples of color:

• Chlorophyll, absorbs a high percentage of wavelengths of red and blue light

• Green light is not absorbed, it is transmitted from the surface of the leaf to our eyes.

Electromagnetic radiation

• The ability of molecules to absorb and transmit light energy is the basis for one of the most widely used procedures for determining the concentration of substances in a solution……………………

Spectrophotometry

• is a technique used to measures the amount of light energy that is absorbed or transmitted by a sample

• Spectrophotometer

What’s in that tube?• By creating and measuring a

series of standards, it is possible to quantify the amount or concentration of a substance in a sample– Serial dilution

Spectrophotometry• 1 – start with a blank

The Blank• In order to effectively use a

spectrophotometer we must first zero the machine, we do this using "the blank."

The Blank• The blank contains everything

except the substance of interest which absorbs light.

The Blank• Thus, by zeroing the machine

using "the blank," any measured absorbance is due to the presence of the substance of interest

Standard Curve• Helps determine the concentration

of the unknown

• A graph where the Y-axis represents the absorbance and the X-axis represents the concentration

Spectrophotometry

A few more terms….• 1. Independent variable

– The variable that is being manipulated

• dependent variable responds to the change made to the independent variable

depends on other factors

Example• For example, if you open a faucet

(the independent variable)

• the quantity of water flowing (dependent variable) changes in response--you observe that the water flow increases.

• Hypothesis:– If plants are grown in five different

types of soil, then the plant in Soil 2 will grow the tallest.

– What is our independent variable?

• plants receive the same amount of water

• the same amount of sunlight____________________________• The only thing that is being

changed is the type of soil they grow in, and that is the independent variable