Formula Units Determination for Magnesium Chloride

This video summarizes an experiment performed to experimentally determine the formula ulnits of magnesium chloride.

In the lab the mass of a small sample of magnesium ribbon is measured. The metal is then placed into a beaker and concentrated HCl is added. When the reaction is complete the beaker is heated to drive off water and any unreacted HCl. Safety Note: This should be done in a fume hood to avoid breathing in any HCl fumes!

 After all the liquid has been removed from the beaker a precipitate of magnesium chloride is left behind.
The mass of this compound is measured and compared to the original amount of magnesium to determine the added mass of chlorine. The data collected allows students to calculate the formula units of the magnesium chloride salt.



The reaction is summarized by the following chemical equation.

2Mg  +  HCl → MgCl2 + H2

The compound forms with a 1:2 ratio of magnesium to chlorine. This is because magnesium has two valence electrons which are donated to the chlorine atoms. The chlorine atoms have seven valence electrons which allow them to add one valence electron during the formation of a chemical bond.

I hope this was helpful.

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