Santa Maria College


WHAT IS ALL THE WINING ABOUT - PART 2 - LOOKING AT RED WINE

March 2010

Mentors:

Overview

UV-Vis spectroscopy provides information about the colour of molecules present in a solution, can identify functional groups and is routinely used in chemical and biochemical laboratories, for example to determine known/unknown concentrations of iron in a tablet. Samples are prepared in solution and are placed in a quartz cell which allows ultraviolet and visible light to pass through, whilst glass and plastic only allows visible light to be transmitted. Tungsten emits (visible light energy) and deuterium emits (ultraviolet light energy) and these colours are focussed on a grating which rotates allowing specific wavelengths of light to be passed through a sample and absorption detected. Samples are generally scanned from the visible to ultraviolet wavelength range. Can you see where the visible and ultraviolet wavelengths are situated below? What part of the visible range is higher and lower in energy? The spectrometer compares the light passing through the sample with that passing through the reference cell. The terms "reference cell" or "blank" will be discussed. Bonus points for students can define the importance of these terms. The transmitted radiation is detected and the spectrometer records the absorption spectrum (Absorbance (AU) vs wavelength (l). The energies of light that are absorbed by the molecules in solution tell us the colour of a solution and in experiments, the amount present. If the same solution is measured over time the spectra that are collected can tell you what is happening to the molecules in solution.

Student Presentation



Photos







Comments