Gas Laws & Atmosphere Lab

Gas Laws & Atmosphere Lab

Objectives:

• Collect gas in multiple ways
• Perform at a single replacement reaction, a reaction with a biological catalyst and a combustion catalyst as it relates to gas production.
• Apply gas stoichiometry to each of your experiments to better understand the relationship between moles of gas and volume of gas.

Part 1: Biological gas creation

Scenario – As you read in your pre-lab article, passing gas is a natural process. Although much of the gas you pass comes from swallowing gas, fermentation of poorly digested starches and sugars can cause a bit of fermentation to occur. Although it is the good and bad bacteria in your lower intestine that ferments these carbohydrates in your gut, we will use yeast to study fermentation in class.

Question: How many moles and milliliters of gas are produced by just 0.5g of yeast when combined with 10.0g of sugar for one hour at 30°C?

Reaction: ___ C12H22O11 (s) + ___ H2O (l)  ___CO2(g) + ___C2H5OH (aq)

Part 2: CO2 from combustion

Scenario- Every day you consume fossil fuels in some way. It may be through your use of electricity which is created primarily through the combustion of coal, it may be through getting to and from school or the movie theater, using your gasoline powered combustion engine, or it may be as simple as using your propane grill. Whatever the case may be, even a small amount of fuel can produce a fairly large amount of CO2. Today you will calculate the amount of carbon dioxide created by simply burning a candle for approximately 30 minutes to get a better idea of the carbon dioxide contribution of your daily CO2 use.

Question: How many moles and liters of CO2 are produced by burning a votive candle for 30 minutes?

Reaction: ___C18H38 (s) + ___ O2 (g)  ___ CO2 (g)+ ____ H2O (g)

Part 3: H2 gas production from reacting an acid with Magnesium Metal

Scenario- Certain metals are very reactive when they come into contact with acids, in fact, magnesium will replace hydrogen in the acid, resulting in a solution containing magnesium ions and production of hydrogen gas. As this reaction is fairly quick we will do this reaction in a eudiometer, or gas collecting tube, so we can visually see the volume of gas collected. Collecting gas over water does incorporate a difficulty as we will need to correct for atmospheric pressure AND correct for the water vapor present within the collected hydrogen.

Question: How many moles and how many liters of H2 are produced by reacting approximately 2 cm of magnesium metal with sulfuric acid?

Reaction: ____Mg (s) + ____ HCl (aq)  ____H2 (g) + ___ MgCl2(aq)

Part 1: Biological Gas Creation

Procedures:

1. Measure out 50.0mL of warm water and add it to your cup.
2. Go to the balance and weigh your cup. Add approximately 10 grams of sucrose (table sugar) to the water. Record the new mass. Finally add 0.5g of yeast to your cup and take the final mass. Carefully swirl your cup to mix the ingredients. Place your cup in the incubator at 30°C.

MOVE ON TO WORK ON PART 2 & 3 WHILE YOUR YEAST DO THEIR THING

1. After 45 minutes to 1 hour, return to the incubator and retrieve your cup. Carefully swirl the cup and try to pop any bubbles that have been created. Find the final mass of your yeast – sugar solution.
2. Pour your yeast and water mixture into the waste container. We need to boil the yeast and kill it before sending it down the drain so we don’t add biological waste to the sewer system!

Data Collection – Lab Part 1

Mass of cup & water / End Time
Mass of cup, water and sugar / Temperature in the incubator in °C & K
Mass of cup, water, sugar and yeast immediately after you add the yeast / Mass of cup, water, sugar and yeast at the end of the experiment
Start Time / Today’s Air Pressure

Lab Part 1 Questions

1. Write out the balanced reaction for part 1. Include the states when you write it out.
2. Where did each of the reactants come from? / 3. Where did each of the products go?
4. What chemical or chemicals does the change in mass represent?

Calculations

1. How many grams of CO2 were produced during fermentation?
2. How many moles of CO2 were produced during fermentation?
3. How many L and mL of CO2 were produced during fermentation?
4. How many moles of sugar did it take to produce this amount of CO2? (use stoichiometry)
5. How many grams of sugar did it take to produce this amount of CO2?
6. What percent of the sugar that you added was used by the yeast?

Conclusions

1. What is an object that represents a similar volume to the volume of gas produced by yeast during your experiment?
2. You may remember that your large intestine is where most of this gas is created. What would be the result of addition of gas like this to your
3. Gas-X and Bean-O are each over the counter medications used to treat gas. Research these products and explain how they each work:

Part 2: CO2 from combustion

Procedures:

1. Weigh your candle
2. Light your candle and let it burn for approximately 30 minutes.

MOVE ON TO WORK ON PART 3 WHILE YOUR CANDLE BURNS

3. After approximately 30 minutes blow out your candle CAREFULLY (don’t lose any wax!) and weigh your candle again.

Data Collection – Lab Part 1

Mass of Candle before the experiment / Mass of candle after it burns
Start Time / Air temperature
in°C & K
End Time / Today’s Air Pressure

Lab Part 2 Questions

1. Write out the balanced reaction for part 2. Include the states when you write it out.
2. Where did each of the reactants come from? / 3. Where did each of the products go?
4. What chemical or chemicals does the change in mass represent?

Lab Part 2 Calculations

1. How many grams of wax were burned in your experiment?
2. How many moles of wax were burned in your experiment?
3. How many moles of carbon dioxide were produced in your experiment?
4. How many Liters of carbon dioxide were produce in your experiment? (use PV=nRT)

Conclusion Questions

1. This wax candle is made from petroleum, which is a fossil fuel. How long ago was the CO2 you just produced stored in that bond?
2. Some candles are made from soy, using waxes that came from plants. How long ago was the CO2 produced by a soy candle.
3. Which of the above candles would
be considered “Carbon neutral?”
4. Algae have been genetically modified to produce gasoline. What are the advantages with using algal biofuels over traditional fuels?
5. If you drive 108miles from Eastlake to Disneyland in a car that gets 22.4mpg, how many liters of CO2 are produced?
1.000 gallon of gas weighs 6.216 pounds. 1lb=453.6g
Reaction: ___C8H18(l) + ___O2(g) ___CO2(g) + ___H2O(g)

Part 3

Procedure

1. Fill a 400mL beaker 2/3 full of water. If possible, use water that has adjusted to room temperature. Obtain a piece of magnesium ribbon from your instructor. Measure the length of magnesium ribbon to the nearest 0.1cm. Record the length of ribbon in your data table. Also record the mass of 1m of this ribbon. / OBSERVATIONS AND NOTES

2. Roll the length of magnesium ribbon into a loose coil. Tie it with one end of a piece of thread, approximately 25cm in length, in such a manner that all the loops of the coil are tied together.
3. CAUTION: HCl is caustic and corrosive… Avoid contact with SKIN AND EYES… Carefully pour approximately 10mL of 6M HCl into a 50mL beaker. Then pour the 10mL of 6M HCl into the gas measuring tube or eudiometer.
4. While holding the eudiometer in a slightly tipped position, very slowly pour water from the 400mL beaker into the eudiometer, being careful to layer the water over the acid so they do not mix. Add enough water to fill the eudiometer completely.
5. Lower the magnesium coiled into the water in the eudiometer tube to a depth of about 5cm. Insert the rubber stopper into the open end of the eudiometer to hold the thread in position. The one-hole stopper should displace some water and ensure that no air is left inside the tube.
6. Cover the hole of the stopper with your finger, and invert the eudiometer in the 400mL beaker of water. Clamp the eudiometer tube into position on the ring stand. The acid flows down the tube and reacts with magnesium. / MAKE LOTS of OBSERVATIONS AT THIS STEP:
Mid Lab QUESTIONS:
1. Why does the acid flow to the bottom?
2. Is the acid now more dilute or more concentrated?
3. Describe your observations… what is happening chemically?
7. When the magnesium has disappeared entirely and the reaction has stopped, cover the stopper hole with a finger and carefully transfer the eudiometer tube to a 1000mL graduated cylinder filled with water. Adjust the level of the eudiometer tube in the water so that the levels of the liquids inside the eudiometer and the cylinder are the same. This takes away the effect of the water’s weight on the gasses above it. /
8. Record the room temperature and pressure in the data table
9. Obtain the water vapor pressure of the water at the current room temperature. Record this in your data table
10. Clean up your lab station, wipe down your lab station, and return to your seats.

*At this point complete your data collection for part 1 & 2 of the lab

DATA TABLE
Length of Mg used (in cm)
*to 2 digits after the decimal
Length of Mg used converted to meters
Mass per meter of Mg
*from the white board
Volume of H2 Collected (read this during step 7)
Temperature of H2 collected (room temperature)
*use a thermometer in the air (in K and C)
Barometer Reading
*from the whiteboard
Vapor pressure of water at current room temperature.
*use the vapor pressure chart on the whiteboard

Lab Part 3 Questions

1. Write out the balanced reaction for part 3. Include the states when you write it out.
2. Where did each of the reactants come from? / 3. Where did each of the products go?

Calculations

1a. Determine the volume of H2 collected in L
b. Determine the pressure of H2 collected using Dalton’s Law to correct for the water vapor present. / a.
b.
2. Determine the moles of H2 collected using PV=nRT
3. Calculate the number of moles of Mg that reacted.
a. Use your length of Mg in meters and multiply by the mas per meter to find the mass.
b. Convert your grams into moles using the molar mass of Mg.
4. Using stoichiometry, determine the theoretical number of moles of H2 you should have made based on your reactants.
5. Find the percent error of your reaction:

List 2 unavoidable sources of error

Conclusions

1. Why did you have to correct for the water vapor pressure?
2. In setting up the experiment you might have accidentally introduced a bubble of air into your eudiometer. What effect would this have on your result? Would your experimental value end up higher or lower than expected? Explain your reasoning.
3. When exposed to air, Magnesium ribbon will react with oxygen to produce a thin layer of Magnesium oxide on the surface of the metal. What measurement does this affect? Will this cause your experimental value or your theoretical value to include error? Explain your reasoning.