NH3BH3 + 2H2 -> NH4BO3 + 3H2
309mg = 0.309g - use moles = mass/molar mass equation:
mol(NH3BH3) = 0.309/14+6(1)+10.8 = 0.309/30.8 = 0.01mol
Use stochiometric ratio 1:3 to recognize that you multiply the moles of NH3BH3 by 3 to get moles of H2, 0.01mol * 3 = 0.03mol = mol(H2)
Prepare variables for pV = nRT (pressure in Pa * volume in m^3 = 8.314 * moles of gas (H2) * temperature in kelvin) , rearranging equation to give V = nRT/p
To convert degrees C into Kelvin, add 273: 27 + 273 = 300K
To convert "bar" into Pa - one "bar" = 100000Pa
R is ideal gas constant 8.314
Substitute values into equation V = (0.03) * (8.314) * (300) / (100000) = 7.8448 * 10^-4 m^3
Convert m^3 into cm^3 by multiplying by 1 million 7.48 * 10^-4 m^3 = 748.26cm^3
The 'purity' thing implies that only 90% of the calculated value is the answer - 784.26 * 0.9 = 673.4cm^-3 which is the answer.