An aqueous solution contains 2.0 % NaCl by mass.
(1) Calculate the molality (NOT molarity!) of the solution.
(2) Calculate the mole fraction of the solution.
I know how to solve both but the problem is missing one other compound/element.
I know that molality is moles per kg of the solvent but I don't know what the solvent is. Is it water? Then how many kg of water?
As for the mole fraction, I know that number of moles of NaCl divided by the total number of moles but where will I get that other mole? Is it water again? How many will I use?
Thanks!
exactly what does "aqueous" mean?
So how many grams and moles of water will I use? I know water is missing compound and for the molality calculation, how many will I use? 1 gram and then covert that to kg?
How many moles will I use? One mole?
Nevermind, I got it. It was simply 100g minus 2g of NaCl (mass of the solvent, water).
To solve the problem, let's assume that the solvent is water. This is a reasonable assumption, as water is a common solvent used in many aqueous solutions.
To find the molality of the solution, we need to determine the number of moles of NaCl and the mass of the solvent.
(1) Molality:
Molality (m) is defined as moles of solute per kilogram of solvent. To find the molality, we need to determine the moles of NaCl. We can then divide that by the mass of the solvent (water) in kilograms.
Given: The solution contains 2.0% NaCl by mass.
Assume we have 100 grams of the solution. This means that 2.0 grams of NaCl are present.
To convert grams of NaCl to moles, we need the molar mass of NaCl, which is approximately 58.44 grams/mole.
Moles of NaCl = (2.0 grams) / (58.44 grams/mole) = 0.034 moles
Now, we need to determine the mass of the solvent (water) in kilograms. Since we assumed we have 100 grams of the solution, we can find the mass of water by subtracting the mass of NaCl from the total mass:
Mass of water = (100 grams) - (2.0 grams) = 98 grams
Mass of water in kilograms = 98 grams / 1000 = 0.098 kg
Now we can calculate the molality:
Molality (m) = (0.034 moles) / (0.098 kg) = 0.347 mol/kg (rounded to three decimal places)
Therefore, the molality of the solution is approximately 0.347 mol/kg.
(2) Mole Fraction:
To find the mole fraction of the solution, we need the number of moles of NaCl and the total number of moles in the solution.
In this case, assuming water is the solvent, the total number of moles in the solution will be the moles of NaCl, as there is no other compound given.
Mole fraction of NaCl = Moles of NaCl / Total number of moles
Mole fraction of NaCl = 0.034 moles / 0.034 moles = 1
Therefore, the mole fraction of the solution is 1.