1. Making Solutions of Differing Mass/Volume Concentrations
Lab Manual 3E

2. timeline Tuesday—Lecture, example with spect. Thursday—Perform Lab
Monday—lab write-up due

3. Write-up
Procedures (include directions for spectrophotometer, don’t have to write out for future labs)
Data (insert info. from table 3.9), include absorbance graph of spect. results (done neatly in your lab notebook, not excel)
Data Analysis/Conclusion (1-2 paragraphs)
Thinking Like a Biotechnician (#3 pg 49)—do on notebook paper and attach

4. Prep. for lab 3e
Spect. example
Check for cupric sulfate 5-hydrate

5. Safety
Gloves and googles

6. Background Orange Juice--Concentrate
Solution, solute (chemical), solvent (diwater)
Mass/volume concentration
volume desired (ml) x concentration desired (g/ml) = ____g of solute

7. Lab 3E tips & changes Do calculations in advance—show how units cancel
When making a solution, the solute is measured out first, and the solvent is mixed into the solute
The mass takes up space, solutions are always prepared by raising the solvent to the final volume
Part 1—each solutions is half the concentration of the previous one, the blue color and absorbance should show this
Part 2-the concentrations change when their volumes are made the same

8. Spectrophotometer Turn to page 47, read yellow box
Do Example with colors at end of class

9. 7.1 Using the Spectrophotometer to Detect Molecules
Molecules are too tiny to be seen.
When an indicator solution changes color, that means a molecule of interest is present.

10. Absorbance, Transmittance, and Reflection
Absorbance, Transmittance, and Reflection. A spectrophotometer measures how light interacts with atoms or molecules in a sample.

11. Parts of a Spectrophotometer
Lamp
Prism
Sample holder
Display
How a Spectrophotometer Works
White light hits grating or prism
Light is split into colors of the rainbow
Wavelength knob directs different colors toward sample

12. Colors of Light in the Visible Spectrum
Colors of Light in the Visible Spectrum. Humans can see light with wavelengths of about 350 to 700 nm.
How a UV Spectrophotometer Works. Similar to a VIS spectrophotometer, the UV spec shines ultraviolet light or visible light on a sample, and a detector measures the amount of light that passes through, or is absorbed by, the sample.

13. How Concentration Affects Absorbance
How Concentration Affects Absorbance. If a sample has twice as many molecules as another, it can absorb twice as much light. This is true at any wavelength. It is important to know a sample’s wavelength of maximum light absorbance, so that the difference in absorbance due to concentration is obvious.

14. Vocabulary
Ultraviolet light – a wavelength of light that is used to detect colorless molecules
Spectrophotometer – an instrument that measures the amount of light that passes through (is transmitted through) a sample
Nanometer – 10-9 meters; the standard unit used for measuring light
Visible light spectrum – the range of wavelengths of light that humans can see, from approximately 350 to 700 nm; also called white light
Transmittance – the passing of light through a sample
Absorbance – the amount of light absorbed by a sample (the amount of light that does not pass through or reflect off a sample)
Tungsten lamp – a lamp, used for VIS spectrophotometers, that produces white light (350 – 700 nm)
Deuterium lamp – a special lamp used for UV spectrophotometers that produces light in the ultraviolet (UV light) part of the spectrum (200 – 350 nm)
% transmittance – the manner in which a spectrophotometer reports the amount of light that passes through a sample
Absorbance units – (abbreviated “au”) a unit of light absorbance determined by the decrease in the amount of light in a light beam
Absorbance spectrum – a graph of a sample’s absorbance at different wavelengths
Lambdamax – the wavelength that gives the highest absorbance value for a sample