LAB #6: Determination of the Empirical Formula of Magnesium Chloride
Background: You have observed the reactions of different metals with hydrochloric acid. You will make careful measurements in this lab investigation to determine the formula for one of those compounds- magnesium chloride.
Purpose:
To determine the empirical formula of magnesium chloride by applying mass/mole analysis
Procedures:
Magnesium will be reacted with hydrochloric acid. In method #1, the mass of the magnesium will be measured and the volume of only enough hydrochloric acid to completely react with the magnesium will be determined. The aqueous product will be isolated and measured. In method #2, magnesium solid will remain and be removed and massed before isolating the aqueous product. The molar ratio of magnesium to chlorine in the product will be calculated. A description of the procedures should explain the reasoning for each step. Data should be clearly recorded.
A. Label a clean empty 100 or 150 mL beaker with a grease pencil or permanent marker. Measure and record the mass of the empty 100 or 150 mL beaker.
B. Measure the mass of the beaker with magnesium. Method #2 requires a larger piece of Mg.
Calculate the mass of magnesium to be reacted.
C. Add the acid slowly - drop by drop. Record the number of drops of hydrochloric acid used.
Method #1. Add only enough HCl to completely react with the magnesium. The entire piece of Mg must react.
Method #2. Add only enough magnesium to react with approximately half the magnesium.
D. Record observations of the reaction and magnesium chloride in solution -MgCl2(aq).
E. Determine and record the number of drops per milliliter of your pipet.
(1 mL is approximately 20 drops.)
F. Calculate the milliliters of HCl added
G. Dry the solution overnight to isolate the magnesium chloride. Method #2. The leftover magnesium solid must be removed and rinsed over the beaker. After drying the mass of the Mg must be measured.
H. Measure the mass of magnesium chloride remaining in the beaker.
I. Record observations of solid magnesium chloride MgCl2(s).
J. How would adding excess HCl affect your results?
Think: What would remain in the beaker after drying.
Calculations:
1. Calculate the moles of magnesium consumed.
2. a. Calculate the mass of chlorine in the magnesium chloride produced.
b. Calculate the moles of chlorine in magnesium chloride.
3. Determine the molar ratio of magnesium to chlorine in magnesium chloride.
Show the ratio reduced to simplest whole number ratio.
4. The actual ratio of magnesium to chlorine is 1:2. Calculate your percent error.
5. a. Calculate the percent by mass of magnesium in magnesium chloride.
b. Using your percent by mass, if you had 100 grams of magnesium chloride
how many grams of magnesium? How many grams of chloride?
Lab Procedure Questions:
6. a. Compare the limiting reactants in method #1 and method #2.
b. What error may be avoided by using method #2?
c. Why was the leftover magnesium rinsed over the beaker?
d. Why was the solution dried over night?
Analysis of the Reaction:
7. THE REACTION- Write the balanced formula equation for the reaction. Include states.
8. HYDROCHLORIC ACID- A REACTANT - Hydrochloric acid is an aqueous solution. Describe the ions in solution in hydrochloric acid. Include numbers of protons, electrons and the charges on the ions. How is this solution an acid? What is the possible pH range for an acidic solution?
9. MAGNESIUM METAL- A REACTANT - Magnesium is a metal. Describe magnesium atoms found in the solid magnesium at the beginning of the reaction. Especially the number of electrons and protons and net charge on these atoms. Identify and describe the bond between the atoms of the solid. Explain how this bond allows the solid conducts electricity.
10.MAGNESIUM CHLORIDE- AN IONIC COMPOUND- APRODUCT - Magnesium chloride is an ionic compound. Describe the ions (Include number of protons and electrons). Especially the magnesium ion so you can compare it to the magnesium atom in the reactants. Describe how magnesium chloride as a solid is different from the magnesium chloride in solution. What bonds hold together the solid magnesium chloride? What attractions are involved in the solution of magnesium chloride? Explain when it conducts electricity.
11. MAGNESIUM ATOM TO ION. Compare the magnesium in the reactant to the magnesium in the product. Consider when it is an ion and when it is an atom. What part of the atom has changed? How? Was magnesium reduced or oxidized? Did it gain or lose electrons?
12. HYDROGEN GAS- A PRODUCT - Hydrogen gas is the other product of the reaction. Describe the hydrogen atoms in the hydrogen molecule. Describe the bond that holds together the hydrogen molecule.
13. HYDROGEN IONS TO HYDROGEN ATOMS IN A HYDROGEN GAS MOLECULE.Compare the hydrogen ion in the reactants to the hydrogen atom in the products. Consider when it is an ion and when it is an atom. How is it different? What part of the atom has changed and how? Was it reduced or oxidized? Did gain or lose electrons? Explain.
Additional Calculationsusing the equation, mass and moles:
14. Refer to your balanced equation for this reaction. One mole of magnesium will produce how many moles of magnesium chloride?
15. Based on the mass of magnesium you started with, how many moles of magnesium chloride could you expect?
16. Calculate the number of moles of magnesium chloride actually produced.
17. Calculate the percent yield.
18. Based on the mass of magnesium you started with, how many moles of hydrochloric acid were required to completely react with the magnesium?
19. Calculate the number of moles of hydrochloric acid that were actually added. Use the molarity of the hydrochloric acid and the volume used to determine the number of moles.
Conclusions:
Briefly discuss the accuracy of your results and explain any deviations.