In the laboratory you will be provided with a 1.0 x 10-5 M primary stock solution of fluorescein (MW=332.31g/mol). The calibration curve should include a blank, 0.025, 0.05, 0.075, 0.10, 0.15, and 0.25 micromolar fluorescein solutions. Since you will be using 25 mL volumetric flasks and the smallest mass that you can weigh out is 1.0 gram you will need to prepare a secondary stock. Calculate the weight of primary stock needed and dilute to 100 mL to prepare the secondary solution. What concentration of secondary stock should you prepare?
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To calculate the weight of primary stock needed, we can use the equation:
Molarity (M) = moles (mol) / volume (L)
Since we want to prepare a 100 mL secondary stock solution, we need to calculate the amount of the primary stock solution required to achieve the desired concentration.
First, convert the desired concentration of the secondary stock solution to Molarity (M).
0.025 micromolar = 0.025 x 10^-6 M = 2.5 x 10^-8 M
Next, we need to calculate the moles of primary stock solution required.
Molarity (primary stock solution) = moles / volume
0.00001 M = moles / 0.1 L (since the primary stock solution is given in Molarity and the volume is 0.1 L)
moles = 0.00001 M x 0.1 L = 0.001 mol
Now we can calculate the weight of primary stock solution required using its molar mass.
Weight (g) = moles x molar mass
Weight (g) = 0.001 mol x 332.31 g/mol = 0.33231 g
Therefore, you would need approximately 0.33231 grams of the primary stock solution.
To prepare the secondary stock solution, you need to dilute the primary stock solution to a final volume of 100 mL. However, the smallest mass you can weigh out is 1.0 gram, so you cannot weigh exactly 0.33231 grams. In this case, you would need to weigh out 1.0 gram of the primary stock solution and dilute it to the desired volume of 100 mL.
To calculate the concentration of the secondary stock solution, we can use the equation:
M1V1 = M2V2
Where M1 is the initial concentration, V1 is the initial volume, M2 is the final concentration, and V2 is the final volume.
To find the concentration of the secondary stock solution, we can rearrange the equation as follows:
M2 = (M1V1) / V2
Substituting the values we know:
M2 = (0.00001 M x 0.1 L) / 0.1 L
M2 = 0.00001 M
Therefore, the concentration of the secondary stock solution should be 0.00001 M (or 10^-5 M).