POST-LAB QUESTIONS (solve this before leaving the class and give answers in your

Question

POST-LAB QUESTIONS (solve this before leaving the class and give answers in your notebook) 1. An amount of 1.000 g of caffeine dissolves completely in a minimum of: 45.0 mL of water at 14 °C (cooled water) 5.5 mL of water at 80 °C · 1.5 mL of boiling water a) Assume that you are recrystallizing 2.00 g of impure caffeine. After one recrystallization from 30.0 ml of water you ended up with 1.200 g of purified caffeine. How many grams of caffeine were left in the cooled water? How many grams are impurities or losses? b) If you reduced the volume of the mother liquor to 5 mL, how many grams of caffeine would be left in solution in the cooled solution?

Explanation / Answer

(a)

Mass of caffeine which was left in the 30 mL cooled water = (1/45)*30 = 0.67 g

So, mass of impurities or losses = 2-(1.2+0.67) = 0.13 g

(b)

Mass of caffeine that will remain in 5 mL of the cooled solution = (1/45)*5 = 0.111 g

Hope this helps !

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