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05.04 Gas Stoichiometry Honors

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nailea rosales

on 9 April 2015

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Transcript of 05.04 Gas Stoichiometry Honors

Calculation Answers
Mg(s) + 2 HC1(aq) . H2(g) + Mg12(aq)
Part of the pressure H2= complete pressure - vapor pressure of H20 = 746 mmHg - 19.8 mmHg = 726 mmHg
Moles of magnesium ; (0.0281 grams) (1 mole/24.304 g) = 1.156 x 10^-3 moles
Heretical yeild of H2 gas: (1.156 x 18^-3 moles] 1 mole H2/ 1 mole Mg)= 1.157 x 18^-3 moles
Theoretical mass: (1.156 x 18^-3 moles) (2.82 g/ mole) = 2.336 x 18^-3 g
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Calculation Answers PT 2
Using gas law:
P= {1.1 atm} (768 torr/ 1 atm) - 19.8 torr = 816.2 torr
V= 8.826 L
T= 295 K
Solving for N:
n= FV/(RT)
n= (81602 torr) (8.826 L)/ {(62.3667)(295)} - value of R has units for L tor / mol k
n= 1.153 x 10^3 moles
Mass= (1.153 x 10^3 moles)(2.82 g/ mole) = 2.338 x 16^-3 g
Temperature C
Results From The Lab
Mass of magnesium strip (g) - 0.034
Volume of gas collected (mL) - 32.2
Barometric pressure (atm) - 1.10
Room temperature (C) - 24.0
Vapor pressure of the water (torr) - Get from vapor pressure table
Measure and cut a piece of magnesium ribbon 3.5 to 4.5 cm long. Do not exceed 4.5 cm.
Measure the mass of the magnesium ribbon to the nearest milligram (0.001 g) and record the mass.

Fold up the magnesium ribbon into a small, tight bundle. Tie it with a piece of thread (10 to 15 cm long).
Add about 10 mL of 3.0M HCl to a gas collection tube.
Hold the gas collection tube at an angle as you fill it completely with tap water, until it is nearly overflowing. Holding the tube at an angle allows the air bubbles to escape.
Place the magnesium in the mouth of the gas collection tube so that it is about three cm below the surface of the water. Fold the thread extension over the side of the tube. Insert a one-hole stopper into the opening so that the magnesium ribbon is held firmly in place.
Fill a 400-mL beaker half full with water.
Holding your finger over the hole in the rubber stopper, invert the tube into the 400-mL beaker of water. Clamp the gas collection tube in place on the ring stand so that the stoppered end of the tube is under the water but not touching the bottom of the beaker.

Warning: Even though the acid has been diluted by the water, be sure to wash your hands after handling the gas collection tube.
Observe the reaction. When no more hydrogen bubbles are visible, the reaction is complete. Tap the tube gently to release any hydrogen gas bubbles on the side of the tube.
Wait an additional five minutes so that the hydrogen gas reaches room temperature.
Cover the hole in the stopper with your finger and transfer the tube to a large cylinder filled with water. Lower or raise the tube until the liquid level on the inside of the tube is the same as the outside. Record the volume of the hydrogen gas inside the gas collection tube. (Be sure to read the liquid level at eye level.)
Measure and record the temperature and pressure of the lab room.
Obtain the appropriate vapor pressure of water from the table below and record.
05.04 Gas Stoichiometry Honors
Table 2
Mass of Magnesium strip (g) - 0.0304
Volume of gas collected (mL) - 10
Barometric pressure (atm) - 1.1
Room temperature (C) - 21
Vapor pressure of the water (torr) - 18.7
Write the balanced equation for the reaction conducted in this lab, including appropriate phase symbols.

Determine the partial pressure of the hydrogen gas collected in the gas collection tube.

Calculate the moles of hydrogen gas collected.

If magnesium was the limiting reactant in this lab, calculate the theoretical yield of the gaseous product. Show all steps of your calculation.

Determine the percent yield of this reaction, showing all steps of your calculations.
1. Would the following errors increase, decrease, or have no effect on the calculated moles of gas collected in the experiment? Explain your answers in complete sentences.

a. The measured mass of the magnesium was smaller than the true mass.

b. The actual temperature of the hydrogen gas is lower than room temperature.

2. Explain in terms of particle collisions and Dalton’s law why it can be assumed that the total pressure inside the gas collection tube is equal to the atmospheric pressure outside of the tube.

3. If an undetected air bubble was trapped inside the gas collection tube, how would this affect your calculated percent yield? Explain your answer.
Nailea Rosales
Water Vapor Pressure
Conclusion Answers
1a. I measured less magnesium than there really was so more moles were there & more gas was made
b. The volume of gas rises with rising temperature more volume would be seen if the temperature rises. Do the opposite
2. The particles on the inside & outside of the containers are exerting force.If there were less from the out, the tube would explode. If there was less pressure from the inside, the tube would fall.
3. Because when you measure you yield percentage you would be counting the air bubble that's trapped which isn't what you are trying to measure. So the yield wouldn't be right.
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