Empirical Formula of Magnesium Chloride
Name__________________________
You will determine the simplest formula of a compound (MgxClY) by collecting experimental data. A measured mass of
magnesium metal will be reacted with an excess of HCl. The excess hydrochloric acid will be evaporated, and the mass of
the magnesium chloride product will be measured. This data will be used to calculate the empirical formula for
magnesium chloride.
Wear goggles throughout this entire lab. You are evaporating hydrochloric acid. Avoid inhaling the fumes.
If you must adjust your goggles, please step far outside the lab area to do so.
1. Measure the mass of a clean, dry beaker with a clean, dry watch glass. Record the mass below.
2. Now zero the balance with the beaker on it and add between 0.45-0.55g of Mg metal. Do not use more than 0.55g.
3. Carefully add 50.0mL HCl to the beaker. Record your observations here: ________________________
4. Let mixture react for about 5 minutes. If there are still visible signs of a chemical reaction taking place after 5
minutes, ask Mr. Kim what to do next.
5. After the reaction has completed, heat the mixture on the flame slowly. As the volume of liquid starts to get low, put
the watch glass on top of the beaker to avoid splattering. Avoid splattering the contents out of the evaporating
dish - this is a very hot acid solution!
6. Heat the mixture an extra minute after no visible liquid remains in the beaker. Avoid inhaling the acidic fumes.
Be careful not to overheat the solid that remains, or it will start to “pop”. Do not lose any solid product!
7. Let the apparatus cool, record the mass of the beaker, solid contents, and watch glass. Be careful… Hot glass
looks like cold glass!
Data
Mass (g)
Empty beaker + watch glass
Magnesium only
Beaker, watch glass, and solid magnesium chloride after first heating
Dry magnesium chloride solid only (calculated)
Chlorine only (calculated)
Using your data, calculate the empirical formula of the magnesium chloride by following the steps below.
Show all work.
1. Using your mass of magnesium chloride formed and the magnesium reacted, calculate the mass of chlorine in the
compound.
Mg +
Cl

MgxCly
Mass:
______g
______g
______g
Answer_______________
2. How many moles of Mg reacted?
Answer_______________
3. How many moles of Cl reacted?
Answer_______________
4. What is the simplest mole ratio of Mg to Cl?
Answer ____ mole Mg : ____ mole Cl
5. What is the empirical formula for magnesium chloride based on your experimental data?
Answer_______________
6. Magnesium chloride is an ionic compound. Using the charges of Mg and Cl ions, determine the actual empirical
formula of magnesium chloride.
Answer_______________
7. How does your experimental empirical formula compare to the actual empirical formula of magnesium chloride?
8. If you did not completely dry your magnesium chloride product…
a. How would your moles of chloride be affected? WHY?
b. How would this affect your empirical formula?
9. If some of the solid magnesium chloride product popped out of the beaker and onto the lab bench…
a. How would your moles of chloride be affected? WHY?
b. How would this affect your empirical formula?