Hydrogen gas is used as a fuel instead of fossil fuels. Storage of hydrogen is a
ID: 904218 • Letter: H
Question
Hydrogen gas is used as a fuel instead of fossil fuels. Storage of hydrogen is a challenge. One avenue of research involves chemical storage such as incorporating hydrogen as part of a metal hydride. In the following reaction sodium borohydride, NaBH4, is used as a means for storing and later generating the hydrogen gas in situ where it is needed as a fuel. Application of heat and use of a catalyst drives the reaction forward. NaBH4(s) + 2 H20(I) right arrow NaB02(s) + 4 H2(g) To test the efficiency of the reaction, 0.11 g of sodium borohydride is catalytically decomposed and 244 mL of hydrogen gas is collected over water at 30.0 degree C under an atmospheric pressure of 752 mmHg. Calculate the % yield of the reaction.Explanation / Answer
mass of NaBH4 = 0.11g
moles of NaBH4 = mass / molar mass
= 0.11 / 37.83
= 0.00291
NaBH4 + 2 H2O -------------------> NaBO2 (s) + 4 H2 (g)
1 4
0.00291
1 mol NaBH4 -------------- 4 mol of H2
0.00291 NaBH4 -------------- ??
moles of H2 = 0.0029 x 4 / 1
= 0.01164
from ideal gas equation
pressure = 752 mmHg = 0.9894 atm
PV = nRT
0.9894 x V = 0.01164 x 0.0821 x 303
V = 0.293 L
theoritical volume = 293 mL
actual volume = 244 mL
% yield = (actual / theoritical ) x 100
= (244 / 293 ) x 100
= 83.28%
% yield =83.28%
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