Question

One method of analyzing amino acids is the van Slyke method. The characteristic amino groups (−NH2) in
protein material are allowed to react with nitrous acid, HNO2, to form N2 gas. From the volume of the gas, the
amount of amino acid can be determined. A 0.0604-g sample of a biological sample containing glycine,
CH2(NH2)COOH, was analyzed by the van Slyke method and yielded 3.70 mL of N2 collected over water at a
pressure of 735 torr and 29 °C. What was the percentage of glycine in the sample? CH2(NH2)CO2H + HNO2 ⟶ CH2(OH)CO2H + H2O + N2

Answer 1

Ptotal = pN2 + pH2O
735 mm = pN2 in mm + approx 31mm
Solve for pN2 in mm. Note: You need to look up the vapor pressure of water. I'm guessing at 31 mm at 29 C.
Then PV = nRT
You know P in mm. Convert that to atm.
You know V and R and T. Make T in Kelvin.
Solve for n = mols N2. There is 1 mol N2 evolved for each mole of glycine so mols N2 = mols glycine.
Then grams glycine = mols glycine x molar mass glycine.
Then % glycine = (grams glycine/grams sample)*100 = ?
Note: grams sample = 0.0604 g from the problem. Check my numbers.