Exercise 5. Hydrated Sodium Sulfate

EXERCISE 5. HYDRATED SODIUM SULFATE, Na2SO4-10H2O 

Dissolve about 250 g. of commercial sodium sulfate (Glauber s salt) in 800 cc. of water heated to 35°. (Look up the solubility curve of sodium sulfate to find the explanation for this Sp3 direction.) If the salt is notably impure, the solution should be freed from iron by adding enough bromine water to oxidize the iron and then enough sodium hydroxide to make the solution distinctly alkaline. 

Filter the solution through a folded filter and set it aside in a quiet place to crystallize. The crystals are glassy in appearance and should not be too large or grown together. Drain them on a Witte plate and evaporate the mother liquor for a second crop. They may be obtained as needles as lath-shaped crystals or in a compact, many-sided form. The last named is the most desirable form, and conditions should be varied to avoid supersaturation (Exercise 6) until such crystals are obtained. Meanwhile, prepare some effloresced sodium sulfate by gently warming about 100 g. of the crude crystals until they fall into white powder. Place this powder in the bottom of an empty desiccator and 

References Mellor, II, 667 Friend, II, 117. If available, Faraday s original observations on the efflorescence of sodium sulfate should be consulted Quart. J. Science, 19, 152 (1825) Faraday s Diary, I, 169. 

Additional Exercises Manganese chloride, MnCtrlHiO magnesium sulfate, MgS04-7H20. 

---