Question

You are given a 2.9237 g sample of a substance with the generic formula MCl2(H2O)6. After completely drying the sample (which means removing the 6 moles of H2O per mole of MCl2), the sample weighs 1.5941 g.What is the identity of element M? Write your answer as a chemical symbol.

Answer 1

Answer:

M is cobalt (Co)

Explanation:

Step 1: Data given

Mass of MCl2(H2O)6 = 2.9237 grams

After completely drying the sample (which means removing the 6 moles of H2O per mole of MCl2), the sample weighs 1.5941 g.

Step 2: Calculate mass of water

Mass of water = 2.9237 - 1.5941  = 1.3296 grams

Step 3: Calculate moles water

Moles water = mass water / molar mass water

Moles water = 1.3296 grams / 18.02 g/mol

Moles water = 0.07378 moles

Step 4: Calculate moles of the whole substance

For 1 mol MCl2(H2O)6 we have 6 moles H2O

Number of moles of the whole substance = 0.07378 / 6 = 0.01230 moles

Step 5: Calculate molar weight of the substance

Molar weight = mass / moles

Molar weight = 1.5941 grams / 0.01230 moles

Molar weight = 129.6 g/mol

Step 6: Calculate molar weight of M

Molecular weight of M = 129.6 - (2*35.45)

Molecular weight of M = 58.7 g/mol

M is cobalt (Co)