294 ❯ STEP 4. Review the Knowledge You Need to Score High
Equipment
Buret
Ring stand and clamps
Pipets of assorted volumes
Pipet bulbs
Assorted glassware, including volumetric glasswareMeasurements
You will be making mass measurements of the Fe(NH 4 ) 2 (SO 4 ) 2 ·6H 2 O and the KMnO 4
and many volume measurements of the pipets, volumetric flasks, and the buret.Calculations
For the standardization: from the number of grams of Fe(NH 4 ) 2 (SO 4 ) 2 ·6H 2 O used,
you can calculate the moles of Fe^2 + used. Knowing this, you can determine the moles
MnO 4 - used from the stoichiometry in the overall reaction (1 MnO 4 - : 5 Fe^2 +) and then
its molarity.
For the peroxide titration: from the buret volume and the molarity of the KMnO 4
solution, you can calculate the moles used in the titration, and applying the overall reac-
tion stoichiometry you can get the moles of hydrogen peroxide (5 H 2 O 2 : 2 MnO 4 - ). From
the moles, you can get grams and finally mass percent (assuming the mass of the peroxide
solution is 1.00 g/mL).Comments
Be very careful in making your measurements. The same general procedure can be applied
to a number of other systems.Experiment 9: Chemical and Physical Changes
Synopsis
Commonly this experiment involves separating the components of a mixture by using the
chemical and physical properties of the mixture components. This is the basis of the analy-
sis of commercially available samples such as over-the-counter acetaminophen- or aspirin-
based pain relievers. The binder (many times sucrose), aspirin, and acetaminophen can be
separated by the difference in their solubility in water and organic solvents, their acidity,
and the difference in the way they react with hydrochloric acid and sodium bicarbonate
solutions.Equipment
Büchner funnels
Vacuum filtration apparatus
Separatory funnel
Hot plate or drying oven
Assorted glasswareMeasurements
You will be making mass measurements of the sample, and every time a component is
separated as a solid, it is dried and the mass determined.