After finding that the experimental molecular weight of 88.989 g/mol, its discrepancy percentage was only 27 % compared to the accepted value. With a low discrepancy percentage, this experiment is reliable enough to find an approximation of a molecular weight in an unknownsubstance. The accepted value for the molecular weight is 122.123 g/mol, which is not that far from the calculated molecular weight. Appendixes:Calculating the molality (m), in mol/kg, using the formula T = Kfm. The Kfvalue for lauric acid is 3.9°C•kg/mol:T = Kfm , T = (43.3 ˚C – 37.8 ˚C) = 5.5 ˚Cm = TK fm = 5.5˚ C3.9˚ C ·kg/mol= 1.4102564102 mol/kgCalculating the moles of benzoic acid solute, using the molality and the mass (in kg) of lauric acid solvent:m = 1.4102564102 mol/kg , kg of lauric acid = 0.00804 kg
Jadan Rios February 11, 2019CHEM 1102 – 03 Spring Dr. JingPage 4 of 4m = molesof solutekilogramsof solventmoles of solute (benzoic acid) = molality x kilograms of solvent (lauric acid)moles of benzoic acid = 1.4102564102 mol/kg (0.00804 kg)moles of benzoic acid = 0.011338461 molCalculating the experimental molecular weight of benzoic acid (g/mol): moles of benzoic acid = 0.01133 mol , measured mass of benzoic acid = 1.009 gexperimental molecular weight = 1.009g0.01133mol= 88.989145 g/molCalculating the accepted molecular weight of benzoic acid from its formula, C6H5COOH.H = 1.008 g/mol , C = 12.011 g/mol , O = 15.999 g/molAccepted molecular weight = 6(1.008 g/mol) + 7(12.011 g/mol) + 2(15.999 g/mol) = 122.123g/molCalculating the percent discrepancy between the experimental and accepted values:Experimental = 88.989145 g/mol , Accepted = 122.123 g/molaccepted−experimentalaccpetedx 100 % = percent discrepancy122.123g/mol−88.989g/mol122.123g/molx 100 % = 27.131543 %
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- Spring '14
- Mole, Freezing-point depression, Lauric acid, amounts of benzoic acid