Hydrogen gas is used as a fuel instead of fossil fuels. Storage of hydrogen is a

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 H2O(l) NaBO2(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 °C under an atmospheric pressure of 752 mmHg. Calculate the % yield of the reaction

Explanation / Answer

The complete reaction is

NaBH4(s) + 2 H2O(l) NaBO2(s) + 4 H2(g)

so 38 gm of NaBH4(s) +2*16=32 gm of H2O(l)   Produces 66 gm of NaBO2 + 8 gm of H2

so theoritically yeild , 0.11 gm of NaBH4 will give = (0.11/38) *8 = 0.0231 gm of H2

Given,

244 mL of hydrogen gas is collected over water at 30.0 °C under an atmospheric pressure of 752 mmHg

We know,

PV =nRT

1 mm of Hg =

0.00131578947 atm

P = 752 mmHg = 752*0.00131578947 atm = 0.98947 atm

V = 244 mL = 0.244 L

R = 0.082 057 46 L atm K1 mol1

T = 30 +273 = 303 K

Now , n = PV/RT = 0.98947 * 0.244 / (0.082 057 46*303) = 0.0097102 moles

So, weight of H2 produced = 0.0097102 moles * Molecular mass = 0.0097102*2 g = 0.0194204 grams

So, percent yeild will be = (0.0194204/ 0.0231 )*100 = 84.07 %

Thank you

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