Lab Report Help

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Created By: Andrew Weeldreyer
Mrs. Wolf Period:3

AP Chem
Lab Report: Determination of the Molar Volume of a Gas

Objective: To react Mg and HCL and form hydrogen gas, then after collecting lab data, determine the hydrogen gas’s molar volume at STP through calculation.

Materials: -LabQuest data collector
- 3.0 M of HCl solution
- Ribbon of Mg metal
- Gas pressure sensor
- Temperature probe
- 600 mL beaker
- 125 mL Erlenmeyer flask
- 20 mL gas syringe
- Rubber stopper with two-way valve
- Plastic tubing
- Analytical balance

Procedure: 1.Retrieve an Erlenmeyer flask then determine its volume.
2. Obtain a Mg ribbon from teacher then make sure to polish until sample is a metallic silver then measure ribbon on a analytical balance then place in flask, afterwards record mass in your data.

3. Fill a large beaker with room temperature water.
4. Start up LabQuest and attach the pressure and temperature probe.
5. Connect a rubber stopper to the pressure probe and later to the flask with valve closed so that absolutely no hydrogen gas will escape.
6. Posses a five mL sample 3.0 M HCl solution and place in a syringe. Connect syringe to the two-way valve on stopper
7. Place the Erlenmeyer flask in the water bath, and begin to collect your data.
8. After a handful of seconds open up your two-way valve and add the HCl solution to the flask, then immediately close the valve.
9. Swirl flask with hands in the water bath until reaction and data collection has concluded.

Data Table:
| Trail One| Trail Two|
Mass of Mg (g)| 0.012 g| 0.014 g| Volume of flask (mL)| 146.0 mL| 146.8 mL| Maximum Pressure (atm)| 1.07 atm| 1.09 atm| Initial Pressure (atm)| 0.991 atm| 0.990 atm| Change in Pressure (atm)| 0.079 atm| 0.1 atm| Temperature (K)| 296 K| 295 K| Vapor pressure in water (atm)| 0.0277 atm| 0.0261 atm|

Analysis: I) Pre-Lab Questions
A. Use Dalton’s law and the vapor pressure of water at 22 C to calculate the partial pressure of hydrogen gas collected.
(746 mmHg)-(19.8 mmHg) = 726 mmHg Hydrogen gas

B. Use the combined gas law to calculate the “corrected” volume of hydrogen gas collected.

(726 mmHg)*(.031 L) = (760 mmHg)*(V2)
(295 K) (273 K)
6144.138 = 224200(X)
V2= 0.027 L of H2 gas

C. What is the theoretical number of moles of hydrogen that can be produced from 0.028 g of Mg?

0.028 g Mg x 1 mol Mg x1 mol H2 = .0012 mol H2
24.305 g 1 mol Mg
D. Divide the corrected volume of hydrogen by the theoretical number of hydrogen to calculate the molar volume (L/mol) of hydrogen at STP.

0.027 L H2
0.0012 mol H2 = 22.5 L/mol H2 at STP

II) Post Lab Questions

1. Calculate the mass of each piece of magnesium that you used if an analytical balance was unavailable? 0.012 g Mg and 0.014 g Mg 2. Calculate the number of moles of each piece of magnesium that you used.

0.012 g Mg x 1 mol Mg = 4.9 x 10.4 mol Mg for trial one.
24.305 g
0.014 g Mg x 1 mol Mg = 5.8 x 10-4 mol Mg for trial two....
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