Question

A mixture of 1.65×10²¹ molecules of X and 1.85×10²¹ molecules of Y weighs 0.688 grams. The molecular weight of X is ( if molecular wt of Y is 187 )

Answer 1

Here, we have,
187 gm of Y = 1 mole of Y = 6.022 x 10^23molecules of Y
So, if 6.022 x 10^23 molecules of Y = 187 g
then, 1.85 x 10^21 molecules of Y = (187 / 6.022 x 10^23 ) x 1.85 x 10^21 = 0.574 gm of Y
Hence, mass of 1.65 x 10^21 molecules of X = 0.688 -0.574 = 0.114 gm
Since, mass of 1.65 x 10^21 molecules of X = 0.114 gm
So, mass of 6.022 x 10^23 molecules of X = (0.114/ 1.65 x 1021 ) x 6.022 x 10^23 = 41.6 gm = mass of 1 mole of X
Hence, molar mass of X = 41.6 gm