Question

Determine the formula for a hydrated crystal that was found to contain 0.88 g CoCl2 and 0.74 g H2O

Answer 1

First step is to find the number of moles of each CoCl2and H2O in one molecule of the compound. Molar mass for water is 18 gm/mole and for CoCl2 is 129.839 gm/mole. Number of moles, n are given by\[n=\frac{sample Mass}{molar Mass}\]Sample mass is 0.88 g for CoCl2 and 0.74 g for H2O.
Now find the molar ratio M\[M =\frac{n_{CoCl_2}}{n_{H_2O}}\]This gives us the number of moles of CoCl2 that combine with 1 mole of H2O. Put this into the formula as\[M(CoCl_2).H_2O\]Simplify so that each molecule has an integral coefficient and you'd have the formula for the hydrated salt.