What is the mole fraction of solute and the molal concentration for an aqueous solution that is 19.0% NaOH by mass?

19% w/w NaOH means 19 g NaOH/100 g soln or 19g NaOH/(19g NaOH + 81 g H2O)

moles NaOH = grams/molar mass
moles H2O = grams/molar mass
XNaOH = moles NaOH/total mols.

m = moles NaOH/kg solvent.
moles NaOH from above. kg solvent from above.

To find the mole fraction of solute and the molal concentration for an aqueous solution, we need to follow these steps:

Step 1: Convert the given mass percentage of solute to grams.

In this case, we have a solution that is 19.0% NaOH by mass. Let's assume we have 100 grams of the solution.

So, the mass of NaOH in the solution is 19.0 grams (19.0% of 100 grams).

Step 2: Calculate the moles of NaOH.

To find the moles of NaOH, we need to know its molar mass. The molar mass of NaOH is calculated by adding the atomic masses of its individual elements.

The atomic mass of Na (sodium) is approximately 23 grams/mol, the atomic mass of O (oxygen) is approximately 16 grams/mol, and the atomic mass of H (hydrogen) is approximately 1 gram/mol.

Thus, the molar mass of NaOH is 23 + 16 + 1 = 40 grams/mol.

To calculate the moles of NaOH, we divide its mass (19.0 grams) by its molar mass (40 grams/mol):

moles of NaOH = 19.0 grams / 40 grams/mol

Step 3: Calculate the mole fraction of solute.

The mole fraction of a component in a solution is calculated by dividing the moles of that component by the total moles of all components.

In this case, NaOH is the solute, and water (H2O) is the solvent. Since the solute is NaOH and we have calculated its moles, we only need to consider this compound's moles for finding the mole fraction.

The mole fraction of NaOH is given by:

mole fraction of NaOH = moles of NaOH / (moles of NaOH + moles of H2O)

Since we only have moles of NaOH, the mole fraction of NaOH simplifies to:

mole fraction of NaOH = moles of NaOH / moles of NaOH

Step 4: Calculate the molal concentration.

The molal concentration is defined as moles of solute per kilogram of solvent. In this case, the solvent is water (H2O).

Since we only have moles of NaOH (as calculated in Step 2), we need to convert the moles of NaOH to kilograms of water.

The mass of water can be calculated by subtracting the mass of NaOH from the total mass of the solution:

mass of water = total mass of the solution - mass of NaOH

In this case, we assumed the total mass of the solution to be 100 grams.

mass of water = 100 grams - 19.0 grams

Next, we convert the mass of water from grams to kilograms:

mass of water = (100 grams - 19.0 grams) / 1000

And finally, we calculate the molal concentration using the moles of NaOH and the mass of water:

molal concentration = moles of NaOH / mass of water (in kilograms)

Now, you can substitute the values into the respective formulas to find the mole fraction of solute and the molal concentration.

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