Question

what do you understand by terms mass percent and mole fraction​

Answer 1

MASS PERCENT
Its simply the mass ratio of different elements of a compound converted onto percentage.

Its always better to explain with example. For eg. 44 grams of CO2 contains 12 g Carbon and 32 g Oxygen and hence the mass percentage of Carbon is 12/44*100 i.e. 27.27%.

Sometimes the average molecular mass is given and you are asked to find mass percentage of the compound. In such a case,

we know,

no. of moles of an element (in a compound) = mass of the element / molar mass of the element

And,

[no. of moles * molar mass + no. of moles’ * molar mass’] / total no. of moles = average molecular mass

i.e. for CO2, we have

let the percentage of C atoms by mass be x and hence the mass percentage of O2 molecules will be (100-x)

And hence, for some given molecular mass of a mixture of CO2,

[x/12*12 + (100-x)/32*32] / x/12 + (100-x)/32 = given molecular mass.

When Further simplified, we have,

100/ [x/12 + (100-x)/32] = molecular mass of the mixture.

And we can easily obtain the value of x.

MOLE FRACTION

Mole fraction is another way of expressing the concentration of a solution or mixture. It is equal to the moles of one component divided by the total moles in the solution or mixture. a = the component that is being identified for mole fraction.

OR

Mole fraction is the ratio of moles of a particular component to the total number of moles of a solution.

If a substance ‘A’ dissolves in substance 'B' and their number of moles are n^A and n^B respectively; then the mole fractions of A and B are given as:

●Mole fraction of A (X^a)

=(no. of moles of A )÷(No. of moles of solution)

=n^A÷ ( n^A + n^B)

● Mole fraction of B (X^b)

=(No. of moles of B )÷(no. of moles of A + no. of moles of B)

=n^B÷(n^A+n^B)

Remember,

X^a + X^b=1.

Answer 2

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