Question

A hydrated compound has an analysis of 18.29% Ca, 32.37% Cl, and 49.34% water. What is its formula?

Answer 1

`CaCl_2;6 H_2O`

Explanation:

Change the percentages to grams. If there was 100 grams then Ca would have 18.29 grams Chorine would have 32.37 grams and 49.34 grams of water.

The grams can be changed to moles by dividing the number of grams by the grams per mole that you can find from the periodic table.

`(18.29/ 1) / ( 40/ 1)` = .45 moles Ca

`(32.37/1) / (35.4/1)` = .91 moles Cl

`(49.34/1) / ( 18.0/1)` = 2.74 moles `H_2O`

Now that the moles of each element ( compound) is known it is possible to find a whole number ratio of the elements and compounds giving an empirical formula.

`.91/.45`= 2 2 Cl : 1 Ca

`2.74/.45` = 6 `6 H_2O` : 1 Ca.

So the empirical formula is `CaCl_2: 6 H_2O`

Ca = +2 Cl = -1 so `Ca Cl_2` is balanced so

the empirical formula is also the molecular formula.