1) If exactly 100.0 grams of NaCl (mm=58.44g/mol) are dissolved in 300 grams of water (mm=18.02g/mol), the mole fraction of NaCl is?
a) 1.71
b) 0.0932
c) 0.250
d) 0.103
e) 4.75
I did 100g / 100g + 300g = 100/40 = 0.250.
Did I do this correctly?
No. mole fraction NaCl = moles NaCl/total moles.
moles NaCl = grams/molar mass NaCl
moles H2O = 300/molar mass H2O
Ok so 100/58.44= 1.71
yes. 1.71 mol NaCl
300/18.02 = 16.65
XNaCl = 1.71/(1.71+16.65) = ?
Ok now I got 0.0931, so this is the mole fraction for NaCl?
yes.
No, you did not calculate the mole fraction correctly. To calculate the mole fraction of NaCl in the solution, you need to use the formula:
Mole fraction = Moles of NaCl / Total moles in the solution
Step 1: Calculate the number of moles of NaCl:
Moles of NaCl = Mass of NaCl / Molar mass of NaCl
Moles of NaCl = 100.0g / 58.44g/mol = 1.71 mol
Step 2: Calculate the number of moles of water:
Moles of water = Mass of water / Molar mass of water
Moles of water = 300g / 18.02g/mol = 16.65 mol
Step 3: Calculate the total moles in the solution:
Total moles in the solution = Moles of NaCl + Moles of water
Total moles in the solution = 1.71 mol + 16.65 mol = 18.36 mol
Step 4: Calculate the mole fraction of NaCl:
Mole fraction = Moles of NaCl / Total moles in the solution
Mole fraction = 1.71 mol / 18.36 mol = 0.0932
So the correct answer is b) 0.0932.