Question

1. Take a 150 mL Erlenmeyer flask from the Containers shelf and place it on the workbench.

2. Add 10 mL of 6 M Hydrochloric acid (HCl) to the Erlenmeyer flask. Dilute with 10 mL of water.

3. Double-click on the Erlenmeyer flask to open the Item Properties window. Choose Close and click OK to plug the Erlenmeyer flask with an airtight stopper.

4. Take a thermometer and a pressure gauge from the Instruments shelf and attach each to the Erlenmeyer flask.

5. Record the temperature, volume of gas and pressure of the gas in your Lab Notes. The gas fills the volume of the flask not filled with liquid or solid. So the volume of the gas is 150 mL minus the volume of liquid. (Remember to press Save Notes so you don’t lose your calculations.)

6. Add 0.1 g of magnesium (Mg) to the Erlenmeyer flask and observe the reaction. Record your observations — there should be at least two indications that a reaction has occurred.

(You may want to use the + or – zoom buttons in the lower right of the screen for a closer view.)

7. The temperature in the flask will peak and then cool. As the temperature inside the flask stabilizes (the temperature change is notably slowed), record a simultaneous reading of the new temperature and pressure.
Wait until the temperature in the Erlenmeyer flask returns to room temperature (21.5 °C), then record the new temperature and pressure.

8. Drag the pressure gauge and thermometer to the recycling bin.

9. Take a gas syringe from the Instruments shelf and attach it to the Erlenmeyer flask. The gas under pressure in the Erlenmeyer flask will expand into the gas syringe in order to equalize with the room pressure of 1 atm (or 14.697 psi). ﾠ

10. Record the final volume and pressure of the gas in your lab notes.

(Pass the mouse cursor over the gas syringe and a gray tool tip will briefly display the total volume.)

11. Clear your station by dragging any containers and instruments to the recycling bench beneath the workbench. (Remember to press Save Notes.)

Original Flask Temperature	Original Flask Pressure	Original Flask Volume	Flask Temperature After Reaction	Flask Pressure After Reaction	Final Gas Volume	Final Gas Pressure
21.5 c	1.00
Number of moles of H2 created		Number of moles of Mg reacted			Molar Mass of Mg
Balanced Equation

12. Compare the experimentally determined molar mass of Mg with listed molar mass (24.3 g/mole).

Calculate the experimental error according to:

% error = | experimental molar mass - listed molar mass | / (listed molar mass) * 100%

% Error

Results

Answer the following questions in the report you submit. Lab Notes and detailed calculations should accompany submitted report. Use the area below to supply your notes and your report.

1)       Write balanced equation for single displacement reaction.

2)       How many moles of H₂ were created?

3)       What is the calculated molar mass of Mg?

4)       What is the experimental error?

Notes and Report:

My Lab Notes

I added 10 mL of water to the flask.
I added 10 mL of hydrochloric acid to the flask.
I closed the flask.
The temperature was 21.5.
The pressure was 1.00.
The volume of the liquid is 20, so the gas is 130.
I put .1 g of magnesium into flask.
The pressure went to 1.83 and dropped to 1.76.
The temperature went to 34.7 and dropped to 21.6
The volume of the gas is 130.1.
After inserting the gas syringe, the volume of the gas in the syringe was 99.5.
The new temperature was 21.5.
The new pressure was 1.00.
The final liquid volume in the flask is 19.9.

Answer 1

Let's understand what is happening here :

S when H2O is added to Acid HCl , HCl dissociates into

HCl ------> H⁺ + Cl ^-

now when Mg strip is added, following reaction takes place

HCl(l) + Mg(s) -----------> MgCl₂ (l) + H₂ (g)

H2 gas is formed and Mg strip dissolves in the solution.

Now,

Answers to the experiment

1)       Write balanced equation for single displacement reaction.

Ans: 2HCl(l) + Mg(s) -----------> MgCl₂ (l) + H₂ (g)

2)       How many moles of H2 were created?

volume of gas before Mg is added = 130 ml

volume of gas after Mg is added = 130.1 ml

gas formed during the reaction = 0.1 ml

Assuming ideal gas law , n = PV/RT

P = 1.83 atm, R = 0.0821 L atm/ mol K

the volume of the gas in the syringe was 99.5 ml = 0.0995

moles of H2 gas formed = 1.83 X 0.0995 /0.0821X 286.25 = 0.003505 moles

moles of H2 gas formed = 0.003505 moles

Moles of Gas = Moles of Metal (moles of M)

3)       What is the calculated molar mass of Mg?

Moles of Gas = Moles of Metal (moles of M)

molar mass of Mg experimental = mass of Mg / moles of H2 = 0.1g / 0.003505 = 28.53 g/mol

4)       What is the experimental error?

Mol wt Mg theoretical ---> 24.305 g/mol

molar mass of Mg experimental ------> 28.53 g/mol

% error = [experimental molar mass - listed molar mass ] / (listed molar mass) * 100%

(28.53 - 24.305 / 24.305) X 100 = 17.38%