HELP!
What is the mole fraction of KCl in a 0.20 molal solution of KCl? (molar mass of KCl = 75 g; molar mass of water = 18 g)

Question

HELP!
What is the mole fraction of KCl in a 0.20 molal solution of KCl? (molar mass of KCl = 75 g; molar mass of water = 18 g)

anonymous · Answer

@thomaster

thomaster · Answer

0.20 molar, that means 0.2 mol per liter
How many moles water are in 1 liter? (1 gram water = 1 ml)

anonymous · Answer

Ml stands for moles?

anonymous · Answer

H2O molar mass = 18.0152 g/mol
 1000 g / 18.0152 g/mol = 55.51 mol????

thomaster · Answer

That's correct.
Now we have 0.2 mol KCl in 55.51 mol H2O
Do you know how to calculate the KCl mole fraction?

anonymous · Answer

no

thomaster · Answer

$\sf\large mole\ fration = \dfrac{moles\ solute}{total\ moles\ in\ solution}$

anonymous · Answer

ok 0.2/55.51?

thomaster · Answer

almost right, the total moles in solution is everything added up. so 55.51+0.2
That makes $\sf\dfrac{0.2}{55.71}$

anonymous · Answer

oh okay. that would be 0.00359002??

thomaster · Answer

Yes :)

anonymous · Answer

that's it??

anonymous · Answer

can you help me with some questions? please! I only have 9 left

thomaster · Answer

Sure, make sure to close this question and post a new one for every question.