Determination of Percent sulfate in Alum
Sections to include:
Data Analysis ( Include volume calculation and balanced equation.)
Pre-weigh about 1 gram of the alum using a top loader scale and weigh boat,
Then use the analytical balance to find a more accurate mass of the alum. Transfer it quantitatively to a 250 mL Beaker.
Calculate the volume of 0.20 M Ba(NO3)2 required to totally precipitate this amount of alum, then add twice this volume of Ba(NO3)2 slowly, while stirring.
Cover the beaker with a watch glass and place the beaker in the fume hood and allow to stand overnight.
Obtain a labeled Gooch crucible that has been cleaned by pulling distilled water through it and then drying it in an oven at 110 for at least 1 hour, then cooled to room temperature.
Determine the mass of the crucible using an analytical balance.
Filter the precipitate through the Gooch crucible using suction. Do not fill the crucible too full as the barium sulfate has a tendency to “creep” up the sides. Wash the beaker and then the precipitate several times with small quantities of distilled water.
Carefully transfer the Gooch crucible to a beaker and dry it in an oven. Allow the crucible to cool and determine its mass.
Calculate the percent sulfate present in the alum and compare to the value calculated from its formula.
CHANGES IN EXPERIMENTAL PROCEDURE, INSTRUCTIONS GIVEN VERBALLY:
This procedure was following, but the precipitate went through the filter because it was a coarse grade filter. The students then were told to filter using gravity filtration with a fine, ashless filter paper.
The filter paper with precipitate was allowed to sit overnight.
Meanwhile, the students practiced burning off on ashless filter paper in a crucible over a burner. I verbally gave instructions as to how to do this, and drew a diagram of how to fold the filter paper so as to minimize loss.
The next day, the students burned the filter paper with the precipitate, stored the crucibles in a desiccator overnight, and weighed the precipitate the next day.
Those who also had some precipitate in the Gooch crucible with the fritted disk dried the crucibles in the oven and were instructed to add the mass of this precipitate to the mass of the precipitate obtained by burning off the ashless filter paper.
Verbal instructions were given for all of this. Students had no instructions as to how to do any calculations, however.
They received a handout that described uncertainty that provided an example of error propagation using a titration.
Write up for Synthesis of Alum Lab
Title Name, Date
Pl(b) Materials and Equipment:
Data and Observations: (Include uncertainties, labels, units)
Calculation of Actual Yield (labeled, with units)
Calculation of Theoretical Yield (labeled, with units)
Calculation of Percent Yield (labeled, with units)
Answer the questions on the handout (except for #8, which is done in the Data Analysis section). You need not write an evaluation other than this.
Writeup for Analysis of Sulfate in Alum
THE FOLLOWING WILL BE GRADED FOR IB and need only contain the following sections:
Title Name, Date
Show all setups, even for calculation of uncertainty.
Be very thorough. State results. Compare to literature value. Discuss limitations of experiment and make suggestions