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. What concentration of secondary stock should you prepare?
To prepare 100 mL of secondary stock, what weight of primary stock do you need to weigh out? Give your answer in grams.
To determine the concentration of the secondary stock solution, we can use the formula:
C1V1 = C2V2
where C1 is the concentration of the primary stock solution, V1 is the volume of the primary stock solution (which is unknown), C2 is the desired concentration of the secondary stock solution, and V2 is the volume of the secondary stock solution.
Given:
C1 = 1.0 x 10-5 M
C2 = 0.025 µM = 2.5 x 10-5 M
V2 = 100 mL = 0.1 L
Let's substitute the values into the formula and solve for V1:
C1V1 = C2V2
(1.0 x 10-5 M)V1 = (2.5 x 10-5 M)(0.1 L)
V1 = (2.5 x 10-5 M)(0.1 L) / (1.0 x 10-5 M)
V1 = 2.5 L
Since we're using a 25 mL volumetric flask, and the smallest mass that can be weighed out is 1.0 gram, we need to calculate the weight of the primary stock solution needed.
Density (ρ) = Mass (m) / Volume (V)
Rearranging the formula, we get:
Mass (m) = Density (ρ) x Volume (V)
Assuming the density of the primary stock solution is close to the density of water (ρ = 1 g/mL or 1 g/cm³):
m = (1 g/mL) x (2.5 x 10-3 L)
m = 2.5 g
Therefore, you need to weigh out 2.5 grams of the primary stock solution to prepare 100 mL of secondary stock.
To calculate the concentration of the secondary stock solution, we can use the dilution formula:
C1V1 = C2V2
Where:
C1 = concentration of the primary stock solution
V1 = volume of the primary stock solution used
C2 = concentration of the secondary stock solution
V2 = final volume of the secondary stock solution
We know that the primary stock solution concentration is 1.0 x 10^-5 M and we want to prepare 100 mL of secondary stock solution. Let's substitute these values into the formula:
(1.0 x 10^-5 M) x V1 = C2 x (100 mL)
We need to find the value of V1, which is the volume of the primary stock solution we need to measure out. However, we don't have enough information to directly calculate it.
Next, we need to calculate the weight of primary stock solution we need to weigh out. To do this, we'll use the molarity and molecular weight of the primary stock solution:
Molarity (M) = (moles of solute) / (liters of solution)
We can rearrange this formula to calculate the moles of solute:
moles of solute = Molarity (M) x liters of solution
We are given the molarity of the primary stock solution as 1.0 x 10^-5 M and the volume as 25 mL (which is 0.025 L when converted to liters). Let's substitute these values into the formula:
moles of solute = (1.0 x 10^-5 M) x (0.025 L)
Now, to find the weight of the primary stock solution, we can multiply the moles of solute by the molecular weight:
weight of solute = moles of solute x molecular weight
The molecular weight of fluorescein is given as 332.31 g/mol. Let's substitute these values into the formula:
weight of solute = (moles of solute) x (molecular weight)
= [(1.0 x 10^-5 M) x (0.025 L)] x (332.31 g/mol)
Now, we can calculate the weight of the primary stock solution in grams.
Note: It is important to use proper lab techniques and equipment for weighing and measuring volumes accurately.