- Background Information
See Background Information (Section II) in Lab Documentation.This material can be handed out prior to the lab, or lectured upon by the instructor.
- Lab Preparation and Equipment
- Several barium salts such as the carbonate, oxalate, chloride, nitrate, sulfate, and phosphate ~5g/person
- Soluble salts like KOH, NaF, Na2SO4, Na3PO4, Na2CO3,and NaCl 0.1 g/person
- 0.1M Ba(NO3)2 10 mL/person
- NH4H2PO4 6g/person
- BaCl2 10g/person
- 3M and 6M ammonia 20 mL/person
- 1M and 0.3 M HNO3 10 mL/person
- 1M and 0.1 M H2SO4 5 mL/person
- 0.1M NH4MoO4 0.5 mL/person
- 0.1M AgNO3 0.5 mL/person
- 3" test tubes
- Quantitative, ashless 11 cm filter paper (S&S No. 589 Blue Ribbon or equivalent)
- 500 mL dropping/separatory funnel
- 500-mL filter flask with Walter crucible holder
- One neck 14/20 500 mL round-bottom flask
- 14/20 size D Buchner type filter funnel (Ace catalog number 9439-08)
- ~25 pounds of soil from a nursery
- small (4-6") aluminum loaf pans
- Tips for Success
Quantitative analysis of solubility
- This procedure can also be used on highly soluble compounds. The accuracy is improved if the compound is stirred with a glass rod during extraction.
- Accuracy can be improved for highly insoluble, finely divided compounds by using an E porosity Buchner-type filter funnel.
- In general the Buchner filter funnels can be cleaned by running 3 M nitric acid through the funnel under aspiration for contaminants that contain the anion of a weak acid, and by using 3 M ammonia for AgCl conaminants. In any case, the use of soap and water is recommended.
- ACS grade barium sulfate does not work well for this analysis. The compound tends to form an unfilterable suspension when water is added. The barium sulfate made during a gravimetric analysis (see Quantitative analysis of barium) works well, however.
- The barium hydrogen phosphate used for this analysis was prepared by combination of barium chloride and sodium dihydrogen phosphate in water.
- We have found no appreciable difference in the solubility of barium carbonate using water in the pH range 4.5 - 7.0.
Preparation and analysis of alforsite
- The pH of the solution in the Erlenmeyer flask is affected by carbon dioxide. If desired, the uptake of carbon dioxide can be minimized by using a Bunsen valve on the top of the flask: Glass tubing with a slit rubber policeman is placed into a one-hole rubber stopper and should provide ventilation but minimize absorption of carbon dioxide.
- Barium hydrogen phosphate precipitates immediately upon combination of the reagents. It is only with heating and stirring for several days that alforsite forms.
- In order to dissolve alforsite, a minimum amount of nitric acid must be added with stirring, followed by distilled water. Barium nitrate precipitates out in nitric acid solution (common ion effect), so water must be added to dilute the solution.
Quantitative analysis of barium
- Even after digestion for several hours, the barium sulfate precipitate is too fine to be collected by vacuum filtration. The particle size can be increased, according to some recipes, by making the filtrate 3% in HCl, which increases the solubility of the barium sulfate and produces a larger particle size.
Quantitative analysis of chloride
- Volumetric analysis with silver nitrate and indicators such as phenosafrinin and dichlorofluoroscein were attempted without success due to the pH requirements in dissolving alforsite and the small chloride concentrations.
- Safety and Hazards
All work should be performed in a hood using gloves and a lab coat/apron to prevent inhalation, spills onto clothing, etc. As always, safety glasses or goggles must be worn. All residues should be placed in appropriate waste bottles.
CAS Registry Numbers
- KOH: 22,147-3
- NaF: 21,530-9
- Na2-SO4: 20,785-3
- Na3PO4: 34,248-3
- Na2CO3: 22,348-4
- NaCl: 20,443-9
- Ba(NO3)2: 20,275-4
- NH4H2PO4: 20,400-5
- BaCl2 x 2H2O: 21,756-5
- Ammonia: 1336-21-6
- HNO3: 7697-37-2
- H2SO4: 7664-93-9
- (NH4)2MoO4: 27,790-8
- AgNO3: 20,505-2