Chemistry Molarity

Question

A 3.366 g sample of an unknown hydrate of cobalt(II) bromide is heated until all the water of hydration is removed. The CoBr2 that remains has a mass of 2.319 g. (a) How many moles of CoBr2 are in the sample? (mol) (b) How many grams of water were lost in the dehydration? (g) (c) How many moles of water were lost? (mol) (d) What is the value of "n" in the formula CoBr2 · n H2O? (1, 2, 3, 4...)

Answer 1

molar mass Co(II)Br2 = 218.7 g/mole

(a) moles Co(II)Br2 = 2.319 g x 1 mol/218.7 g = 0.01060 moles

(b) mass of H2O in the dehydration = 3.366 g - 2.319 g = 1.047 g

(c) moles of H2O lost = 1.047 g x 1mole/18.015 g = 0.05812 moles

(d) 0.05812 moles H2O/0.01060 moles CoBr = 5.5

n = 6