Question

A hydrated blue copper(II) sulfate salt with a formula YCuSO4•XH2O is heated until it is completely white in color. The student who performed the dehydration of this salt took note of the mass of the sample before and after heating and recorded it as follows: Mass of hydrated salt = 500 g mass of dehydrated salt = 320 g. What is the value of 'X' in the formula of the hydrated cell?

Answer 1

Answer:

X = 5

Explanation:

The molar ratio of water to copper(II) sulfate must be found.

The mass of water that must have been eliminated from the salt is found by the difference in weight before and after:

(500 g) - (320 g) = 180 g water eliminated

The moles of water (MW 18.02 g/mol) is then found:

(180 g) / (18.02g/mol) = 9.9889...mol

The mass of the dehydrated copper(II) sulfate (MW 159.609 g/mol) is converted to moles:

(320 g) / (159.609 g/mol) = 2.004899...mol

The molar proportion of water to the copper(II) sulfate is then calculated:

(9.9889...mol H₂O) / (2.0034899...mol CuSO₄) ≅ 5