November 11, 2014
In this lab,
Materials that are needed for this lab:
1.) Lab balance
2.) 2 small beakers
3.) 2 200-mL beakers
4.) Bunsen burner with lighter
5.) Ring stand with ring and clay triangle
6.) Stirring rod
7.) Filtration funnel
8.) Ash less filter paper
9.) Wash bottle with distilled H20
10.) 2 porcelain crucibles
11.) 6 M HCl
12.) 0.25 M BaCl2
13.) 0.05 M AgNO3
14.) PPE’s (goggles and lab coat)
1.) Weight out two samples of unknown, each weighing 0.3 to 0.5 g as follows. Transfer the sample directly from the vial into separate beakers of at least 400 mL capacity. Transfer the sample by tapping the vial while holding it sideways over the beaker. Be careful not to lose any sample when moving the vial to and from the beaker.
2.) Dissolve each sample in about 200 mL of water and add 5 mL of 6 M HCL.
3.) Heat each solution nearly to boiling and add 25 mL of 0.25 M BaCl2 while stirring for a period of about five seconds. Allow the precipitates to settle.
4.) Test the supernatant solutions for complete precipitation by adding about 3 mL of BaCl2 solution. Add more BaCl2 solution if necessary.
5.) Maintain the suspensions of BaSO4 at about 90 degrees for 40 to 60 minutes. If the precipitate has aged satisfactorily, it should settle out, leaving a clear supernatant a few minutes after the beaker is allowed to stand undisturbed.
6.) Immediately after the heating of the BaSO4 suspension, the filtration can be started. If at least one uninterrupted hour is available for the filtration, cover the beakers and store them until the next laboratory period. (Stop experiment here)
7.) Clean and dry two porcelain crucibles and heat them on a clay triangle over a burner to drive off any water. After they have cooled to room temperature, carefully weigh each crucible to 0.1 mg. Allow the crucibles to cool on the triangle with the burner turned off.
8.) Prepare two funnels with ash less filter paper.
9.) Separately decant the supernatants from the BaSO4 precipitates through the filter paper cones into waste flasks.
10.) When most of the solution in each beaker has been decanted, stir up the remaining slurries of BaSO4 in the beakers and transfer the precipitates to the filters. By using at least three 15-mL portions of hot water, quantitatively transfer the BaSO4 to the filters.
11.) Wash the precipitates with about eight small portions of hot water, directed at the upper edges of the filter paper. Take