Help with Beer's Law lab experiment question! So we were told to calculate the concentration of 5 standard solutions but I don't know how to do that exactly. The Concentration of the solution in flask B was .0024 M and our lambda max (max absorption) was at 515 nm. I know the formulas but I'm confused as to where to start first and how. I'd appreciate if someone could show me one example from the five below.
Vol. of B solution % transmittance
25mL 31
20mL 42
15mL 55
10mL 67
5mL 82
For #1, did you take 25 mL of 0.0024 M and dilute it to some volume? What volume? The concn will be
0.0024M x (25 mL/final volume)= ?? M
After you know concn, then
A = log (1/T) = a*c (assuming the path length was the same throughout and it probably was). Knowing T and c you can calculate the constant, a for each of the five and calculate an average for a.
To calculate the concentration of the standard solutions using Beer's Law, you will need the equation for Beer's Law, which is:
A = εbc
Where:
A = Absorbance
ε = Molar absorptivity (a constant that depends on the substance and wavelength)
b = Path length (the width of the cuvette or flask holding the solution)
c = Concentration
In this case, you are given the volume of solution B and the percent transmittance for each volume. To calculate the concentration, follow these steps:
Step 1: Convert percent transmittance to absorbance.
- Absorbance (A) can be calculated using the formula:
A = -log(T/100) or A = log(1/T)
Where T is the percent transmittance.
- Calculate the absorbance for each percent transmittance value in the table provided.
Step 2: Plot a calibration curve.
- The concentration (c) is the variable we want to calculate.
- Plot the absorbance values you calculated on the y-axis against the respective known concentrations on the x-axis.
- In this case, you will have five data points, one for each volume of B solution.
Step 3: Determine the equation for the calibration curve.
- Fit a best-fit line through the data points on your graph.
- This line represents the relationship between concentration and absorbance.
- You can use graphing software or line-fitting techniques to find the equation of this line.
Step 4: Calculate the concentration for the unknown.
- Once you have the equation for the calibration curve, plug in the absorbance value of the unknown solution (volume of B solution) to calculate its concentration.
For example, let's say you want to calculate the concentration for the solution with a volume of 20 mL and a percent transmittance of 42.
1. Convert percent transmittance to absorbance:
A = -log(42/100) = -log(0.42) = 0.376
2. Plot a calibration curve:
- Plot the absorbance value of 0.376 on the y-axis against the respective known concentrations on the x-axis.
3. Determine the equation for the calibration curve:
- Fit a best-fit line through the data points and find the equation for the line, such as y = mx + b.
4. Calculate the concentration for the unknown:
- Plug in the absorbance value (0.376) into the equation for the calibration curve to find the corresponding concentration.
Repeat these steps for the other four volumes of B solution to calculate the concentrations for each unknown solution.
Note: Make sure to use a solution with a known concentration as a reference or calibration standard to ensure accurate results.