NAME: PERIOD: 3Universal Gas Law Constant Lab

Objective: To experimentally determine the universal gas law constant.

Materials: eudiometer ruler magnesium ribbon beaker thread tap water stopper thermometer barometer apron ring stand clamp safety goggles hydrochloric acid

Procedure: 1. Measure the length, in centimeters, of the magnesium ribbon. Record.2. Gently curly the Mg(s) into a spiral form. Tie a long piece of thread to it. Leave

about3. 10.00-cm extra thread on the end.4. Your teacher will add hydrochloric acid to the eudiometer.5. Tilt the eudiometer and fill the rest of the tube with cold water. Try not to mix the

water and acid by gently pouring the water down the side of the eudiometer.6. Fill a large beaker halfway with tap water.7. Place the Mg (s) floating on top of the water in the eudiometer allowing the string

to hang over the outside of the tube. Close the eudiometer with a one-holed stopper.

8. Place your finger over the hole in the stopper. Invert the eudiometer and place the stopper end in the large beaker of water. Remove your finger when the stopper is below the water level. Clamp the eudiometer into place making sure that the eudiometer is not sitting on the bottom of the beaker. (See Figure 29-2)

9. Observe until all the magnesium ribbon is completely reacted. Record observations.

10. Record the temperature of the water in oC. Convert the oC to Kelvin.11. Record the volume of the gas in milliliters. Convert the milliliters to liters.12. Record the barometric pressure in kPa. Convert kPa to atmospheres (1.00 atm = 101.3 kPa).13. Using the REGENTS Reference Table H, record the water’s vapor pressure in kPa. Convert kPa to atmospheres14. atm = 101.3 kPa).15. Clean up according to the verbal instructions.

DATA/OBSERVATION: (Insert Data/Observation Table below)

Mass of Magnesium Ribbon

Temperature of Water

Volume of Gas Barometric Pressure Observations

4.09g 291.9 K .03701 L 1.01 atm The magnesium ribbon reacted with the Hydrochloric acid producing bubbles and the magnesium began to disappear and brake apart

1. During a chemical change, matter is not created nor destroyed, only rearranged. Therefore, according to the balanced chemical reaction below, when the reaction is completed, the MOLES of magnesium used are equal to the MOLES of hydrogen gas produced. For this step.

Mg (s) + 2 HCl (aq) → H2 (g) + MgCl2 (aq)

Given the length of the magnesium ribbon, calculate the moles of magnesium ribbon reacted in the lab. Show the numerical factor-label set-up and record your answer to contain “3” significant figures.

1.00 meter of magnesium = 0.7956 g

4.09 cm * .01 m * 0.7956 g * 1 mole = .00134 moles 1 1 cm 1.00 m 24.3 g

2. In this lab, the hydrogen gas was collected "over water." This means that the gas produced was in contact with liquid water. The consequence of this is that the gas in the tube WILL NOT be pure H2. The gas in the eudiometer is a MIXTURE of H2 (g) and H2O (g). Use Dalton's Law of Partial Pressure and partial pressure of the gaseous H2O (vapor pressure) to calculate the partial pressure of the H2 gas in atmospheres. Show the numerical set-up and record the answer to the 1/100th place.

PH2= Atmospheric Pressure - Vapor pressure of H2O

= 1.005973736 atm- 0.021710527 atm= .984263209 atm= .984 atm

3. Calculate the universal gas constant (R), in L•atm/moles•K using the ideal gas law equation. Show the numerical set-up and record the answer to contain “3” significant figures.

PV= nRT(.984atm)(.03701L)= .00134(R)(291.9K).03641784 = .391146 R.391146 . 391146 R=.0931

4. Calculate the percent error. Show the numerical set-up and record the answer using the rules of significant figures.

Percent Error= Accepted Value- Experimental Value * 100 Accepted Value

= .0821-.0931 * 100 .0821Percent Error= -13.4

Practice Problems:

5. A sample of hydrogen gas has a volume of 8.56 L at a temperature of 0.0oC and a pressure of 1.50 atm. What is the mass of the hydrogen gas? Show the numerical set-up and record the answer using the rules of significant figures.

PV= nRT

(1.50)(8.56)= n(.0821)(273)

12.84 = 22.4133n22.4133 22.4133

n= .5729 moles

.5729 moles * 2.0 grams = 1.1 grams 1 1 mole

Mass of H2= 1.1 grams

6. A sample of methane gas, CH4, has a volume of 1.75 L at STP. What is the mass of the methane gas? Show the numerical set-up and record the answer using the rules of significant figures.

PV=nRT

(1.00)(1.75)= n(.0821)(273)1.75 = 22.4133n22.4133 22.4133

n= .0781 moles

.0781 moles * 16.0 grams = 1.25 grams 1 1 mole

1.25 grams of CH4