I have to prepare a 0.2% water solution of n-propanol and a water solution of methanol and isopropanol at 0.2% that can be in the same container. It didn't specify but I'm pretty sure the solutions are v/v%.
For the n-propanol a 0.2% solution should just be 2mg/mL of solution and the mg can be converted using the density to calculate the volume of n-propanol required, that I understand. What confuses me though is the second solution which is methanol and isopropanol in the same container, do I put 1mg worth of both methanol and ispropanol (after converting) in a mL of water OR do I make two separate 0.2% solutions of each and mix them together.
If you interpret the question to be to prepare 0.2% solution methanol and 0.2% solution of isopropanol, and you want to put them in the same container, you add the volume of each required as if the other component were not there. Remember that if you prepare them separately and mix them that each will dilute the other when the final solution is made.
Oh that's true, so you're saying to measure out the amount of methanol needed for a 0.2% solution and the amount of isopropanol needed for a 0.2% solution, adding both to the same 1 mL of water, correct?
yes
To prepare a 0.2% water solution of n-propanol, you are correct that you can start by calculating the volume of n-propanol required using the density of n-propanol. The density of n-propanol is typically around 0.803 g/mL.
Here's how you can calculate the volume of n-propanol required:
1. Determine the mass of n-propanol needed for a 0.2% solution. Since the concentration is given in v/v%, you can assume that it refers to milliliters (mL) of alcohol per 100 mL of solution. So, a 0.2% solution means you need 0.2 mL of n-propanol per 100 mL of solution.
2. Convert the volume to mass using the density of n-propanol. The mass of n-propanol needed is 0.2 mL * 0.803 g/mL = 0.1606 g.
3. To prepare the solution, dissolve 0.1606 g of n-propanol in enough water to make a total volume of 100 mL.
Now, for the second solution containing methanol and isopropanol in the same container, you have a couple of options:
Option 1: Mixed Solution
1. Calculate the volume of methanol required for a 0.2% solution of methanol in water, following the same steps as for n-propanol.
2. Calculate the volume of isopropanol required for a 0.2% solution of isopropanol in water, using the same approach.
3. Mix the calculated volumes of methanol and isopropanol together.
4. Dilute the mixed alcohol solution with enough water to make a total volume of 100 mL.
Option 2: Separate Solutions
1. Calculate the volume of methanol required for a 0.2% solution of methanol in water, following the same steps as for n-propanol.
2. Calculate the volume of isopropanol required for a 0.2% solution of isopropanol in water, using the same approach.
3. Prepare separate solutions of methanol and isopropanol by dissolving the calculated volumes of each alcohol in enough water to make a total volume of 100 mL.
4. Mix the prepared solutions of methanol and isopropanol together in the desired container.
Both options will result in a final solution containing both methanol and isopropanol at a concentration of 0.2% each, and n-propanol at a concentration of 0.2% as well. The choice between the options depends on whether you want the methanol and isopropanol in separate solutions or mixed together.