SOLUTION PREPARATION AND BEER’S LAW
Concepts in this experiment are also discussed in sections 1.6, 2.8, 3.7, 4.4, 7.2, 12.3, 12.5 of
Principles of Chemistry : A Molecular Approach
, Nivaldo J. Tro .
A history of Kool-Aid
be found at:
This is a two-part experiment.
In part A, you and your lab partner will prepare solutions of your
In part B, those solutions are used to construct standard Beer’s
Law plots of absorbance vs. concentration.
The best-fit lines for those plots are then used to
determine dye concentrations in Kool-Aid
of known and unknown dilutions.
Background material includes topics not covered in your lecture text.
The experiment employs
the Vernier colorimeter; the Vernier system is used extensively in Gen Chem II Lab (Chem 1034).
Solution preparation employs foundation lab skills: weighing rapidly as accurately as required,
transferring material quantitatively, mixing thoroughly, measuring volumes, and calculating
This experiment can help you assess and further develop your expertise.
For quantitative work we need to know the amount of solute in solutions.
Because it’s facile
operationally, concentration is most commonly measured as
), which is defined as:
Molarity is a measure of the number of solute molecules present per liter of solution.
A mole is a
named number (like a dozen or a googol); but at 6.022 x 10
, is more than the former (1.2 x 10
and less than the latter (10
A solution’s molarity is the number of moles (or fraction of a mole)
of solute per liter of solution.
The amount of solvent is not measured (contrast with
whose advantage is that mass can usually be measured more precisely than volume).
PREPARATION OF A SOLUTION USING A PURE, SOLID SOLUTE
For 3-4 significant figure accuracy, weighed, dry solute is dissolved in less than the required
volume of solution in a volumetric flask (choose Class A for highest accuracy).
(and adjusting to near the glassware’s calibration temperature, typically 20°C) is complete, add
solvent, and mix again.
Add more solvent with a transfer pipet to bring the solution level up to the
fill line on the flask’s neck.
The bottom center of the liquid’s meniscus should be level with the top
of the line.
Stopper or cap the flask; hold the top in place and support the base.
invert the flask gently, swirl it, and revert it until mixing is essentially complete (up to 40 times, at
least a few times beyond when inhomogeneity – streaking – is still visible).
For example, how should 250 mL of 0.200 M CuSO
solution be prepared given copper(II) sulfate
O (lovely blue crystals) and deionized (DI) water?