Pre-Laboratory Assignment 10 Section Molar Volurne of Hydrogen Rea collected by

Question

Pre-Laboratory Assignment 10 Section Molar Volurne of Hydrogen Rea collected by water displaceanenrat 22 °C The bar-netric pressure in the lab was 746 mum le n gn. The gas was The apw pessure of water an 22 198e Den' ne tw culase the parial pre gen gas in the gas-collecting tuhe. se the combined gas law to calculate the "corrected" volume of hydrogen at STP: Hint: Watch your units for temperature and pressure 3. What is the theoretical number of moles of hydrogen that can be produced from 0.028 g of Mg Hint: Refer to Equation I for the balanced equation for the reaction. Divide the corrected volume of hydrogen by the theoretical number of moles of hydrogen to calculate the molar volume (in L/mole) of hydrogen at STP 4.

Explanation / Answer

Q1

Ptotal = Sum of Pgases

Ptotal = Pgas + Pvapor

Pgas = Ptotal - PVapor

Pgas = 746 - 19.8

Pgas = 726.2 mm Hg

Q2

T = 22°C = 22+273 = 295 K, V = 31 mL = 31*10^-3 L, Pstd = 760

P1V1/T1 = Pstd*Vstd/Tstd

substitute

726.2 *(31*10^-3) / 295 = (860)(Vstd)/(273)

Vstd= 726.2 *(31*10^-3) / 295 *273/860

V = 0.02422 L

V = 0.02422*10^3 mL = 24.22 mL

Q3

mol of Mg = mass/MW = 0.028/24.3 = 0.00115

ratio is

1 mol of MG = 1 mol of H2

0.00115 mol --> 0.00115 mol of H2

Q4

0.00115 mol of H2 --> 22.4*0.00115 = 0.02576 L of H2

%yield = real/ theoreticla*100 = 0.02422 /0.02576*100 = 94.02%

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