A 1.1% (w/w) solution of cocaine hydrochloride (molar mass 339.81 g/mol) in water. Calculate the molal concentration.
Is it 0.0297 mol/kg?
To calculate the molal concentration of a solution, you need to know the moles of the solute (cocaine hydrochloride) and the mass of the solvent (water).
Given:
- Mass percentage of cocaine hydrochloride in water: 1.1% (w/w)
- Molar mass of cocaine hydrochloride: 339.81 g/mol
To determine the moles of cocaine hydrochloride, you'll need to know the mass of the solution. Let's assume we have 100 grams of the solution. Therefore, the mass of cocaine hydrochloride in the solution is 1.1 grams (1.1% of 100 grams).
Next, you can convert the mass of cocaine hydrochloride into moles using its molar mass. Divide the mass by the molar mass to get the number of moles:
moles = mass / molar mass
moles = 1.1 g / 339.81 g/mol
moles ≈ 0.00324 mol
Now, let's consider the mass of the solvent (water). Since 100 grams of the solution are assumed to be present, and the mass of cocaine hydrochloride is 1.1 grams, the mass of water is:
mass of water = total mass - mass of cocaine hydrochloride
mass of water = 100 g - 1.1 g
mass of water = 98.9 g
Finally, you can calculate the molal concentration by dividing the moles of cocaine hydrochloride by the mass of the solvent (in kg):
molal concentration = moles / mass of water (in kg)
molal concentration = 0.00324 mol / (98.9 g / 1000)
molal concentration ≈ 0.0328 mol/kg
Therefore, the molal concentration of the 1.1% (w/w) solution of cocaine hydrochloride in water is approximately 0.0328 mol/kg, which is not the same as 0.0297 mol/kg.