Question

A 0.514−mol sample of a metal oxide, M2O3, weighs 77.0 g.

(a) How many moles of O are in the sample?

(b) How many grams of M are in the sample?

(c) Which element is represented by the symbol M? (Give the elemental symbol of that element.)

Answer 1

Ans a) Here for the given sample of 0.514 mol of metal oxide M₂O₃ ,there is 3 'O' atom

Therefore moles of 'O' = (0.514 mol M₂O₃ x 3 mol 'O') / 1mol M₂O₃

                                 = 1.542 mol 'O'

b) In order to calculate the mass of M ,we will calculate the mass of O in the sample

mass of 'O' = 1.542 mol O x 16 g of O / 1 mol O

                  = 24.672g

Now,

total mass of M₂O₃ = 77g

mass of O = 24.672g

mass of M=77-24.672

                = 52.328g

c) for the given sample of 0.514 mol M₂O₃ there is 2 M atom

Now, moles of M = 0.514 mol M₂O₃ x 2 mol M / 1mol M₂O₃

                          = 1.028 mol of M

therefore number of moles of M = 1.028

Given mass of M= 52.328g

Molar mass of M = Given mass /number of moles

                          = 52.328 /1.028

                           = 50.902 g/mol

We know the atomic mass of vanadium is 50.941 which is quite close to our calculated molar mass

Therefore the element M is vanadium (V)