Chemical Formula Determination Laboratory
Pre-Laboratory Assignment
Refer to the section in your textbook on determining chemical formulas if you need help with the
calculations below. You must be comfortable with mole calculations and the concept of ratios.
1. The formula for Epsom salt is MgSO4·7 H2O. What does the chemical formula become when
this hydrate is gently heated? ________
2. A 1.00-g sample of an unknown hydrate of cobalt chloride is gently dehydrated. The
resulting mass is 0.546g. The cobalt is isolated and weighs 0.248g. What is the formula of the
hydrate? Make sure you use an adequate number of significant figures, or your answer
could be incorrect.
a) Determine the mass of water lost from the hydrated unknown.
__________________
Determine the number of moles of water lost from the hydrated unknown. _________________
b) Determine the mass of cobalt collected.
Determine the number of moles of cobalt collected.
__________________
__________________
c) Determine the mass of chloride in the compound.
Determine the number of moles of chloride in the compound.
__________________
__________________
d) What is the mole ratio of chloride to cobalt? If you divide your two numbers, then the
denominator, cobalt, is equal to 1 (round to a whole number for answer in blank). _______ : 1
e) What is the mole ratio of water lost (numinator) to cobalt (denominator)? Divide your
numbers so that the denominator will equal 1 (round to a whole number to put in blank). ____: 1
f) Use the answers from parts d and e to determine the chemical formula of the cobalt chloride
hydrate. It will have the form CoxCly · z H2O, where x, y, and z are integers that you determined
from parts a through e.
Complete formula of the unknown cobalt chloride hydrate: ______________________________
Name of unknown cobalt chloride hydrate: ___________________________________________
5. In this experiment, you will determine the formula of a copper chloride. Copper usually
exists as +1 and +2 oxidation states. Give two possible chemical formulas you expect for
CuxCly, where x and y are integers.