Making Solutions of Differing %
Mass/Volume Concentrations
Lab Manual 3F
timeline
Monday—Lecture
Tuesday—Perform Lab Part I, II, III
Thursday—Perform Lab Part IV
Write-up
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Procedures (all will do the additional
concentrations)—part IV #4
Data
--3.14 (include additional concentrations)
--3.15 (include additional concentrations)
.3125% and .15625%
Data Analysis/Conclusion (answer all questions in
from the text)
Thinking Like a Biotechnician--#1,2,4 (Skip 3)—
do 4 on notebook paper
Prep. for 3f
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Check for sodium hydroxide pellets,
cupric sulfate 5 hydrate, gelatin,
glass tubes
Set-up spectrophotometer
Background Application Example
Fertilizer—”12-5-7”
12% nirogen, 5% phosporus 7%
potassium in the 5 lb bag
.12 x 5lb=.6lb nitrogen
.05 x 5lb=.25lb phosphorus
.07 x 5lb-.35lb potassium
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Background Biuret reagent
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Copper sulfate and sodium hydroxide make up a
protein indicator called Biuret reagent
2 to 1 ratio of 10% sodium hydroxide and 5%
copper sulfate
When the copper reacts with certain amino acids in
proteins, the solution goes from blue green or
violet.
The darker violet the solution, the more protein is
present
Copper also used as an indicator in Bradford
reagent & BCA reagent as a protein indicator & in
Benedict’s solution for glucose
Background
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Copper sulfate is only good for about 1
week before precipitating out
Gelatin is made from fairly large protein
molecules that do not easily go into
solution, this is why gelatin must be
heated to go into solution.
The protein testing should be conducted
at room temperature, so you need to plan
ahead
Gelatin solutions are fairly concentrated,
to get obvious color difference
Formulas
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Volume desired (ml) x concentration desired (% g/ml converted to decimal value of g/ml)=
____g of solute
Safety Precautions
Sodium hydroxide is dangerous
(wear gloves and googles)—strong
base
 Use hot plates not a flame
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Lab 3F tips
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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