Question

Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is 0.040(assume the density of water to be one).

Answer 1

Mole fraction = 0.04/1 = 1/25.
In 25 moles of the total mixture, 1 mole of ethanol and 24 moles of water are present. 24 moles of water weigh 24 x 18 = 432 g = 432 mL (18g is the molar mass of water)
1 mole of ethanol is present in 432 mL of water. Molarity is no. of moles of solute present in 1 L of solution.
So molarity = 1 x 1000 / 432 = 1000/432 = 2.315 M (approx.)

Answer 2

but wont ethanol also occupy sum volume?

Answer 3

wait

Answer 4

*whistling*

Answer 5

whats the answer?

Answer 6

idk meritnation says ur correct they used the same method

Answer 7

molarity M= (WB/WA)*1000/V
mole fraction of C2H5OH= 0.040
molar wt. of ethanol= 46gm
wt. of ethanol in 1 mole of soln= 46*0.04=1.84
mole fraction of water= 0.960
molar wt. of water= 18gm
wt. of water in 1 mole of solution=17.28
Volume of solution= 1.84+17.28= 19.12ml (1gm=1ml)
therefore,
M= (1.84/17.28)*1000/0.01921
=0.00556 M

Answer 8

is that...??

Answer 9

wth i cant copy
but meritnations answer matches ur first

Answer 10

Quote: "therefore, M= (1.84/17.28)*1000/0.01921 =0.00556 M"

I'm afraid this is wrong.
Answer is [ethanol] ≈ 0.002 mol/L

Answer 11

?plz xplain

Answer 12

hmmmm...

Answer 13

Instead of using formulae, I prefer working out on an numerical example.

I start with 1.00 mole of mixture. What is its composition in moles?
ethanol = ........ mol
water = .........mol.

then for each substance, work out the mass:
ethanol = ........... g
water = ............ g

then volume (assume density of ethanol is similar to that of water, or use the actual value of 0.79):

ethanol = ............. mL
water = .............. mL

Final volume (ignore the slight contraction that appears when you mix ethanol and water):
Final volume = .............. mL

Finally:
[ethanol] = ................. mol/L

Answer 14

@shruti : sorry, I realise now I typed the same answer as yours!

Only your last line was not correst, but everything else was ok!

Answer 15

i dont get it how can i do the first blank
it contains 1 mole ethanol
and how many moles of water?

Answer 16

By definition "mole fraction of ethanol is 0.040" means there is 0.040 mole of ethanol in 1.000 mole of mixture.

Answer 17

i dont think we can assume density of eth and water to be the same. and density of ethanol would have been provided if needed...

Answer 18

If ethanol's density is not provided, it means you have to approximate the final volume.

There are 2 ways out:
- ignore the volume of ethanol completely and the answer is 0.00222
- equate density of eth. and water and answer is 0.00209

Using d = 0.79 yields 0.00204

Real answer is between 0.00204 and 0.00209

Answer 19

its okay vincent.