We are asked to prepare a 100 ml solution with the following 3 concentrations:
53.00 mg/ml sodium salicylate, 0.020 M FeCl3, and 0.050 M HCl.
Then, we are going to take the absorbance at 520 nm.
What is the best way to prepare the 100 ml solution ?
For 53 mg/mL and you want 100 mL so 53 x 100 = 5300 mg of the salicylate, place in a 100 mL volumetric flask, add water and make to the mark on the volumetric flask.
0.02M FeCl3. That means 0.02 mols/L or 0.002 mols/100 mL. How much is 1 mole?
mols = g/molar mass. You know molar mass and mols you need, solve for grams. Place that many grams in a 100 mL volumetric flask and make to the mark with distilled water.
You can follow the same directions as the FeCl3 but that will be hard to do since HCl is a gas. The best way to do that is to use some HCl already made up and dilute it. You will need to know the concn of the stronger solution.
Then mL1 x M1 = mL2 x M2.
Say you had some 1 M stuff, then
mL1 x 1M = 100 mL x 0.05M
Solve for mL1 you need of the 1M.
To prepare the 100 ml solution with the given concentrations, you will need to know the molecular weights of sodium salicylate (NaC7H5O3), FeCl3, and HCl. Here are the steps to prepare the solution:
1. Calculate the mass of sodium salicylate needed:
- Multiply the concentration (53.00 mg/ml) by the required volume (100 ml) to get the total mass of sodium salicylate needed.
- This can be calculated as: mass = concentration x volume.
2. Calculate the volume of FeCl3 solution needed:
- Molarity (M) is defined as moles of solute per liter of solution.
- Since the desired concentration is 0.020 M, you will use this information to calculate the volume needed.
- Calculate the moles of FeCl3 required: moles = concentration (M) x volume (L).
- Convert the moles of FeCl3 to volume using its molarity: volume = moles / molarity.
3. Calculate the volume of HCl solution needed:
- Apply the same process as step 2, using the given concentration of 0.050 M HCl and the desired volume.
4. Add the solutions together:
- Prepare a 100 ml volumetric flask or beaker.
- Measure the calculated volumes of sodium salicylate, FeCl3, and HCl solutions using appropriate measuring tools (graduated cylinder, pipette, etc.).
- Add the solutions one by one into the volumetric flask or beaker, making sure each one is accurately measured.
5. Dilute to the final volume:
- If the final solution is supposed to be 100 ml, add solvent (usually water) to the flask or beaker until the total volume reaches the desired volume.
6. Mix the solution:
- Gently mix the solution to ensure proper distribution of all components.
Now, you have prepared a 100 ml solution with the desired concentrations of sodium salicylate, FeCl3, and HCl. You can now take the absorbance at 520 nm as required.