text: calculate the molar mass of a vapor that has a density of 6.535 g/l at 17°c and 825 torr.?   1 torr 101325 /760 pa =133 pa   825 torrs =133*825 = 1.1* 10^5 pa  calculate n  from pv = nrt  in mksa   r = 8.31jk-1 1l = 10^-3 m^3  n= 1.1 10^5 *10^-3/ 8.31 * ( 273+17)= 0.045mole  so 0.045 mole weights 6.535  and 1 mole = 6.535 /0.045=144