Transcript Measuring small and very small volumes

Making Solutions of Differing
Mass/Volume Concentrations
Lab Manual 3E
timeline
Tuesday—Lecture, example with
spect.
Thursday—Perform Lab
Monday—lab write-up due
Write-up
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Procedures (include directions for
spectrophotometer, don’t have to write out for
future labs)
Data
--3.10 (insert info. from table 3.9), include
absorbance
--3.11
--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
Prep. for lab 3e
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Spect. example
Check for cupric sulfate 5-hydrate
Safety
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Gloves and googles
Background
Orange Juice--Concentrate
 Solution, solute (chemical), solvent
(diwater)
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Mass/volume concentration
volume desired (ml) x concentration desired (g/ml) = ____g of solute
Lab 3E tips & changes
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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
Spectrophotometer
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Turn to page 47, read yellow box
Do Example with colors at end of
class
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.
Absorbance, Transmittance, and Reflection. A spectrophotometer
measures how light interacts with atoms or molecules in a sample.
Parts of a Spectrophotometer
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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
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.
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.
Vocabulary
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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