533580559
Name: ___________________________
Due Date: _________________
Determination of the Percentage Composition
by Mass of Magnesium Chloride
4++
E2
Purpose:
To analyze the reaction between magnesium and hydrochloric acid.
Quantitative analysis of the reaction will allow us to compare the mass of
the reactants to that of the products and to determine the percentage
composition by mass of the solid magnesium chloride.
Pre-lab assignment:
1. Create a flow chart outlining your procedure for this lab on a separate piece of paper.
2. Copy out all safety procedures by hand onto a separate sheet of paper. You will not be
allowed to begin the lab until you have done so.
a) Wear goggles at all times.
b) Keep hair tied back.
c) Secure loose clothing.
3. Copy out first aid measures by hand on separate sheet of paper. You will not be allowed to
begin until you have done so.
a) If spilled on hands, wash thoroughly for 15 minutes.
b) If contact with eyes, flush at eye wash station for 15 minutes.
c) If inhaled, remove to fresh air. If not breathing, give artificial respiration.
d) If ingested, rinse mouth with cold water. Give victim 1-2 cups of water or milk to drink.
Procedure:
1. Measure and record the mass of a clean, dry 250 mL beaker
2. Obtain a sample of magnesium from your teacher. Give it a quick rub with steel
wool or sand paper. Place the Magnesium ribbon into your beaker and record the
mass of the Mg and beaker.
3. Remove the Mg from your beaker.
4. Using a graduated cylinder obtain approximately 15.0 mL of 3.0 M hydrochloric acid
and add it to your beaker. Record the mass of the HCl(aq) + beaker.
5. Drop your magnesium into the HCl(aq) and observe the reaction.
6. When the reaction is complete, record the mass of your beaker and solution.
7. After measuring the mass, place your beaker on a hot plate and carefully boil off all
remaining liquid in the fume hood. When your beaker is dry, observe the remaining
product and record the mass of the beaker + product.
8. Clean your beaker with water and discard contents down the drain. Put away all
apparatus.
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Results and Observations:
Table 1: Qualitative Observations of Reaction between Mg and HCl(aq)
Reaction between
Magnesium
Magnesium
Hydrochloric Acid
Mg and HCl(aq)
Chloride
Table 2: Quantitative Observations and Results
Mass of empty beaker
Mass of beaker + Mg
Total Mass of Mg used
Mass of HCl(aq) + beaker
Mass of HCl(aq) used
Mass of final solution + beaker
Mass of final solution
Mass of dry MgCl2 + beaker
Mass of dry MgCl2(s)
% Mg
Post Lab Discussion Questions
Please answer the following questions in the space provided. Attach your pre-lab to
this sheet.
1. What is the purpose of using the sandpaper or steel wool on the magnesium prior to
starting the lab?
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533580559
2. Use the collected data to determine the percent Mg and percent Cl in your sample
of MgCl2. Compare this to the theoretical percent composition of MgCl2. What
could cause this difference?
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3. The reaction between magnesium and hydrochloric acid produced magnesium
chloride and hydrogen gas, write a balanced chemical equation for this reaction.
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4. Determine the total mass of the HCl(aq) and the Mg(s) used in this reaction. Compare
this to the total mass of the solution after the reaction. Are they the same? If not,
by how much do they differ? How can we account this difference?
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