1. Gas Stoichiometry Lab
CHS
Richard Jackson
2007

2. Data Table: __ Mg + __ HCl  __ + __
Length of Magnesium ______ cm
Mass of Magnesium ______ g
Moles of Hydrogen Gas ______ mol (n)
Actual Yield of H ______ mL
Temperature of water ______ °C
Temperature in Kelvin ______ K
Air Pressure of Room ______ mmHg
Vapor Pressure of Water ______ mmHg
Partial Pressure of H ______ mmHg
Partial Pressure of H ______ atm
Theoretical Yield of H ______ mL
Percent Yield of H ______ %

3. Complete the Single Replacement / Displacement Reaction below and Balance it
__ Mg + __ HCl  __ __

4. Calculate Necessary Mg
Determine length (cm) of Mg needed to produce 25-30mL of hydrogen gas. Determine to 4 decimal places.
Use the balanced equation
Use the 1 mol gas = L gas
Use Mg 24.31g/mol
Use 1cm Mg = grams (this value may vary based on amount of oxidation - )

5. Cut piece of magnesium metal.

6. Get mass of Mg
Use the analytical balance in stock room to get the mass of the metal.

7. Roll up magnesium strip into a little ball.

8. Wrap up magnesium strip in a copper wire cage leaving a 2 inch hook.

9. Mg and Cu Why is a copper cage used?
We are placing the contraption into HCl – what will / won’t happen?

10. Activity Series

11. Add 8 mL of 6 M Hydrochloric Acid into a gas collection tube.

12. Slowly add distilled water, stacking it on top of the acid.

13. Why is acid always added to water, and not the reverse?
A large amount of heat is released when strong acids are mixed with water. Adding more acid releases more heat. If you add water to acid, you form an extremely concentrated solution of acid initially. So much heat is released that the solution may boil very violently, splashing concentrated acid out of the container! If you add acid to water, the solution that forms is very dilute and the small amount of heat released is not enough to vaporize and spatter it.
So Always Add Acid to water, and never the reverse
BE CAREFUL – We are doing the opposite (in tall glassware – so the risk is greatly reduced).

14. Insert magnesium/copper wire cage.

15. Make sure the hook catches

16. Insert the one hole stopper

17. Cover stopper hole with gloved finger and invert the tube.

18. Put the tube into the water before removing your finger.

19. Connect tube to buret clamp
Connect tube to buret clamp. Watch the acid swirl through the water and down the tube.

20. Look- Bubbles!

21. Bubbles

22. Video Clip of Bubbles

23. The temperature = ? °C
30°C
?°C
20°C

24. Convert °C into K
K = °C + 273

25. Measuring the Volume of Hydrogen Gas
Water
level

26. Make the water levels equal The volume is ? mL
Actual Yield ? mL

27. Remove the stopper and dump the remaining water.

28. Pressure Get today’s barometric pressure.
Most stations have it in inches Hg
Convert to mm Hg
1 inch = 2.54cm
1 inch = 25.4 mm

29. 690 mmHg
Room Air Pressure
? mmHg
680 mmHg

30. Dalton’s Law
The pressure above our aqueous solution is not all hydrogen gas. There is also water vapor – it is a mixture.
Dalton’s Law states that the total pressure of a mixture (PT) is equal to the pressure of the individual gases PT = PH2 + PH2O
PT is our atmospheric pressure here at CHS (Hill Field data used).
PH2O , water-vapor pressure, is gathered from the table based on temperature.

31. Temperature - Vapor Pressure Chart

32. Calculate Partial Pressure of H2
PT = PH2O + PH2
PT – PH2O = PH2

33. Convert Partial Pressure of H2 from mmHg into atm
____ mmHg ( atm ) =
( 760 mmHg)

34. Convert mass of Mg into Moles Mg
____ g Mg ( 1 mole Mg ) =
( g Mg )

35. Convert Moles of Mg into Moles H2
____ mol Mg ( ? mol H2 ) =
( ? mol Mg )

36. Calculate the Theoretical Yield of H2 gas in mL
PV = nRT
VH2 = nRT / P
VH2 = ( mol)( L atm) ( K)(1000 mL)
( atm ) mol K ( 1 L )
VH2 = mL

37. Calculate the Percent Yield of H2
Percent Yield = (Actual Lab Yield) x 100 =
(Theoretical Yield)
Percent Yield = ( ) x 100 =
( )
Percent Yield = %

38. The End