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Molar Volume of a Gas LAB

Molar Volume of a Gas LAB. Lab Outline. Pre-Lab Title Purpose (be specific) Procedure Results Data Table – appropriate title, straight lines, etc. - mass of Mg, temperature of H 2 O, volume H 2 gas (measured in the large graduated cylinder) and atmospheric pressure

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Molar Volume of a Gas LAB

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  1. Molar Volume of a Gas LAB

  2. Lab Outline • Pre-Lab • Title • Purpose (be specific) • Procedure • Results • Data Table – appropriate title, straight lines, etc. - mass of Mg, temperature of H2O, volume H2 gas (measured in the large graduated cylinder) and atmospheric pressure • Post-Lab • Calculations • Conclusion

  3. Materials

  4. Eudiometer Preparation 1. Obtain 10 mL of 3 M HCl from acid dispensing bottle – place in small beaker. 2. Place the eudiometer into 1 side of the double buret clamp with the open end up. 3. Using a funnel, transfer the acid to the eudiometer. 4. Fill the rest of the eudiometer with H2O.

  5. Mg Preparation 1. Use steel wool to “shine” your Mg – the cleaner the better! 2. Mass your Mg – make sure it doesn’t weigh more than .045 g, if it does snip some off. 3. Coil up your Mg – not too tight though. 4. Cut a piece of thread (10-15 cm) and tie it around your Mg coil. 5. Cut off the excess thread that is “dangling.”

  6. Let the Reaction Begin 1. Place Mg in the eudiometer (let thread hang out over the side). 2. Place stopper in eudiometer until H2O comes out of the hole in the top of stopper. (HCl is more dense than H2O so the reaction won’t occur yet). 3. Flip your eudiometer, making sure no air gets in. 4. Place the eudiometer back in the buret clamp, with the stopper submerged in H2O in a 250 mL beaker. 5. Gas will displace the H2O as the reaction proceeds.

  7. Be Careful – Air is Bad! 6. Reaction is complete when Mg is gone and there are no more bubbles. 7. Remove the eudiometer from the H2O. 8. Place the eudiometer in the grad. cyl. until the water levels are the same. 9. Read the volume to the nearest tenth. This is the volume of H2 gas at atmospheric conditions. 10.Record the temperature of the water to the nearest tenth oC. 11.Read the atmospheric pressure from the barometer. 12.Clean up – your done!

  8. Calculations • To calculate molar volume (L/mol) of H2, you need 2 things: 1. mol of H2(g) 2. volume of H2 in LITERS (make sure you convert V2 to liters before dividing by moles)! • To obtain mol of H2: • convert mass of Mg to mol of Mg • from balanced equation mol of Mg = mol of H2 • Now, you need to find volume of H2 gas as if it were at STP. P1 = Current Pressure (from lab quest) P2 = 760. mmHg V1 = measured value V2 = ??? T1 = room temp. + 273 T2 = 273 K • Molar Volume of Hydrogen Gas: • L of H2 / mol of H2 (hopefully your answer is close to 22.4) • Percent error: experimental value – theoretical value x 100 theoretical value

  9. Conclusion • Explain clearly (with evidence) how molar volume for H2 was determined. Be sure to make it clear where the value for moles of H2(g) comes from! • Remember to provide explanation for % error. Types of error should fit the degree and direction of error. That is, errors which would give a higher value for molar volume should not be used to explain a negative error.

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