Question

In the first of two experiments, a student is assigned the task of determining the number of moles of water in one mole of MgCl2*nH2O. The student collects the data shown in the following table:
Mass of Empty Container-22.347g
Initial Mass of Sample and Container-25.825g
Mass of Sample and Container after first heating-23.982g
Mass of Sample and Container after second heating-23.976g
Mass of Sample and Container after third heating-23.977g
What I really want to know is how do I find the coefficient in front of H2O. Could you please supply the steps?

Answer 1

The number of moles of water lost when the sample was heated is 0.1026 mol. the formula of hydrated compound is MgCl₂.6H₂O.

When the sample is heated The total number of moles of water lost is given as :

mass of H₂O loss = 25.825 - 23.997

                            = 1.848 g

moles of H₂O = mass / molar mass

                       = 1.848 / 18

                       = 0.1026 mol

mass of anhydrous MgCl₂ = 23.977 - 22.347

                                            = 1.630 g

moles of MgCl₂ = mass / molar mass

                          = 1.630 / 95.20

                          = 0.0171 mol

moles of H₂O per MgCl₂ = 0.1026 / 0.0171

                                         = 5.99 = 6 mol

the formula of hydrated compound = MgCl₂.6H₂O

To learn more about moles here

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