It rate of effusion of a particular gas was measured and found to be 24.0 ml/min. under identical conditions the rate of effusion of methane gas was measured and found to be 47.8 ml/min. what is the molar mass of the unknown gas?

The molar mass of unknown gas is 63.5 g/mol

calculation

let the unknown gas be represent by letter Y  

The rate of effusion of a gas varies inversely with square root of molar mass

that is R(CH4)/ R(Y)= √[(M(Y)/M(CH4)]

= 47.8 ml/min/24.0ml/min= √[(Y/16g/mol)]

square both side to remove square root sign

=47.8²ml/min /24²ml/min= Y/16 g/mol

=2284.84ml/min/576ml/min=Y/16g/mol

multiply both side by 16

y =63.5 g/mol

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.