Question

Mole fraction of A in H2O is 0.2 . The molarity of A in water is....?

Answer 1

Density of water in g/ml is 1. It is a standard value

However for doing the problem we do not require density value and hence the statement is not necessary.


Given

Mole fraction of A = 0.2

decimal 0.2 is same as fraction .

Mole fraction of A =

And here the mixture contains A and
Therefore
mole fraction of

That is if we take 5 moles of mixture we have moles of A and moles of

Moles =

Molar mass of water is 18



4 moles of water means it weigh 72g or 72mL (since 1g = 1mL)

1 mole of A is present in 72 mL of water.

Molarity is no. of moles of solute present in 1 L of solution.

1 mL =

72 mL=

So molarity =
= 13.9 M