What is the mole fraction of NaOH in an aqueous solution that contains 20.5% NaOH by mass?
That's 20.5g NaOH in 100 g soln. The 100 g soln is composed of 20.5g NaOH + 100-20.5 ==> 79.5 g H2O
Convert 20.5g NaOH to moles.
Convert 79.5 g H2O to moles.
XNaOH = moles NaOH/total mols.
XH2O = moles H2O/total mols.
To calculate the mole fraction of NaOH in an aqueous solution, you need two pieces of information: the mass percentage of NaOH in the solution and the molar mass of NaOH.
First, you need to find the molar mass of NaOH. Sodium (Na) has a molar mass of approximately 22.99 g/mol, Oxygen (O) has a molar mass of approximately 16.00 g/mol, and Hydrogen (H) has a molar mass of approximately 1.01 g/mol. Summing the molar masses together gives us a total molar mass of NaOH as approximately 40.00 g/mol.
Next, you need to calculate the mass of NaOH in the solution. If the solution contains 20.5% NaOH by mass, this means that for every 100 grams of the solution, there are 20.5 grams of NaOH. So if you have a known mass of the solution, you can calculate the mass of NaOH using this percentage.
Now that you have the mass of NaOH, you can convert it to moles using the molar mass of NaOH. Divide the mass of NaOH by its molar mass to get the number of moles of NaOH.
Finally, to calculate the mole fraction of NaOH, you divide the moles of NaOH by the total number of moles of all components in the solution (NaOH and water). The mole fraction formula is:
Mole fraction of NaOH = moles of NaOH / (moles of NaOH + moles of water)
Since water (H2O) is the only other component mentioned, the mole fraction of water will be 1 - mole fraction of NaOH.
So, to summarize the steps:
1. Find the molar mass of NaOH (approximately 40.00 g/mol).
2. Determine the mass of NaOH in the solution using the mass percentage.
3. Convert the mass of NaOH to moles using its molar mass.
4. Calculate the mole fraction of NaOH using the moles of NaOH and the moles of water.
Using this method, you can find the mole fraction of NaOH in the given aqueous solution.