PHYSICAL SCIENCES

EXPERIMENT 5

SPECTROPHOTOMETRY DEMONSTRATION

 

 

 

DATE: _______ NAME: __________________ I.D.#: ______ SECTION: _____

 

INTRODUCTION:

All matter is composed of particles that ultimately emit electromagnetic radiation of various forms. Some of this electromagnetic radiation may be due to chemical bonding. The signal from many types of chemical bonds and arrangements of atoms within a structure can be detected by laboratory instruments called spectrophotometers. Spectrophotometers are instruments designed to detect radiation emitted by samples of matter in mainly four regions of the electromagnetic spectrum. These four regions are ultra violet, visible, infra red and radio waves.

Instruments designed to detect radiation in the ultra violet (UV) region of the electromagnetic spectrum are called UV spectrophotometers. This region of the spectrum contain waves which are very high energy. Waves of this kind are emitted by our sun and can be very dangerous to our eyes. The UV region is divided broadly into two categories - short and long waves. The short waves are higher energy waves and are associated with the part of the electromagnetic spectrum where X-rays occur. The long UV waves are associated with radiation approaching the visible region of the spectrum.

Instruments designed to absorb radiation in the region of the spectrum visible to the human eye are call visible/color spectrophotometers. These instruments are capable of detecting all of the range of colors detectable to our eyes. Beta-carotene is a substance found in our eyes that help us to absorb electromagnetic radiation in this region for detection by our brains. Absorbency in this region entails radiation energy associated with certain arrangements chemical bonds within substances.

Instruments designed to absorb radiation in the infra red (IR) region of the spectrum are called IR spectrophotometers  These instruments have the ability to detect the presence of different kind of chemical bonds within a molecule. These signals are emitted at lower energy than our eyes are capable of detecting; however, detection using an IR spectra is very important for identifying substances and determining their molecular structure.

Instruments designed to function in the micowave/radio wave region of the spectrum include such instruments as the microwave oven which emit signals that can be absorbed by the water molecules in food. Nuclear magnetic resonance (nmr) is an area which has recently gained popularity in the medical profession. These waves occur at the lowest energy part of the electromagnetic spectrum and encompass waves that can range from a few centimeters to kilometers.

OBJECTIVE:

To look at rock samples using an ultra violet light source. APPARATUS:

Ultraviolet lamp with short/long wave filters. Rocks with UV absorbing properties. PROCEDURE:

1.    Observe sets of rocks which absorb ultraviolet light and answer the questions below.

2.        Use the UV lamp to observe two sets of rocks (box 1 and box 2). Adjust the slide on the lamp to switch between short wave UV and long wave UV. Observe what happens.

 

 

 

QUESTIONS:

1.    Which box of rocks was affected most by the short wave UV light?    Explain your observations.

2. Which box of rocks was affected most by the long wave UV light? Explain your observations.