(May be on Canvas) Determining the chemical formula of a cobalt chloride hydrate

Question

(May be on Canvas) Determining the chemical formula of a cobalt chloride hydrate A. A student weighed out a 2.055 g sample of a cobalt chloride hydrate, ConClphoo the waters and p are integer values to be determined. The student heated the of hydration, re-weighed the anhydrate sample and found 1.121 g anhydrate sample to drive off the waters 1. What was the mass of H20 driven off 0.934 B. The student then converted this amount of water to moles using the molar mass of water 2. What is the molar mass of water? g/mol 3. How many moles of water were driven off? OS2ml C. The student dissolved the anhydrate in water, and then used a Single Replacement reaction found from the Activity Series for metals to bring the cobalt out of solution. After purifying and drying, the cobalt massed 0.509 g. The student then converted this amount of cobalt to moles using the molar mass of cobalt. 28.13 0082 mol 2 a/mol 4. What is the molar mass of cobalt? 5. How many moles of cobalt were there? D. The student then found the mass of chloride in the original sample by difference, and converted this chloride amount into moles as well. 6. What is the mass of chloride in the sample? 7. What is the molar mass of chlorine? 8. How many moles of chloride were there? g/mol mol

Explanation / Answer

Ans. So far, we have-

            Mass of hydrated sample = 2.055 g

            Mass of H2O = 0.934 g

            Moles of H2O = 0.05189 mol

            Mass of anhydrous sample = 1.121 g

            Mass of Co = 0.509 g

            Moles of Co = 0.00864

Now,

            Mass of Cl = Mass of anhydrous sample – mass of Co

                                    = 1.121 g – 0.509 g

                                    = 0.612 g

            Moles of Cl = Mass / Molar mass

                                    = 0.612 g / (35.4527 g/ mol)

                                    = 0.01762 mol
# Stoichiometric molar ratio of Cl and Co = Moles of Cl / moles of Co

                                    = 0.01762 mol / 0.00864 mol

                                    = 2.04 : 1

                                    = 2 : 1

The molar ratio of Cl : Co = 2 : 1 means that there are 2 Cl-atoms every 1 Co-atom.

So,

            Chemical formula of anhydrous salt = CoCl2

# Moles of anhydrous salt CoCl2 = Mass of anhydrous salt / Molar mass

                                                = 1.121 g/ (129.8386 g/ mol)

                                                = 0.00864 mol

# Stoichiometric molar ratio of H2O and CoCl2 = Moles of H2O / moles of CoCl2

                                                = 0.01762 mol / 0.00864 mol

                                                = 2.04 : 1

                                                = 2 : 1

The molar ratio of H2O : CoCl2 = 2 : 1 means that there are 2 H2O molecules every mole of anhydrous salt.

So,

            Chemical formula of hydrated salt = CoCl2.2H2O

# Summary: n = 1   ; m = 2           ; p = 2

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