The spectrophotometer was used to measure the abosrbance of each of a series of [FeSal]+ solutions. A standard curve was constructed by plotting the absorbance vs. concentration (M). The slope and y-intercept were found to be 1517 M-1 and 0.001, respectively.
Procedure
An aspirin sample was prepared following the procedure given in the experiment. A 0.139 g sample of aspirin was hydrolyzed with 5 mL of 1 M NaOH (reaction 1) and diluted with distilled water to 50.00 mL in a 50 mL volumetric flask, forming solution A. A 1.00 mL aliquot of solution A was diluted to 50.00 mL using 0.02 M Fe(III), forming solution B (reaction 2). The absorbance of solution B was found to be 0.379.
How many moles of [FeSal]+ were in the 50.00 mL of solution B?
To find the number of moles of [FeSal]+ in the 50.00 mL of solution B, we need to use the information provided in the problem statement and the standard curve.
First, let's understand the relationships between concentration, absorbance, and the standard curve.
In the given experiment, a standard curve was constructed by plotting the absorbance (y-axis) against the concentration (x-axis) of the FeSal+ solutions. The slope and y-intercept of this standard curve were given.
The equation for a straight line is generally given by the equation y = mx + b, where "m" is the slope and "b" is the y-intercept.
In this case, the equation of the standard curve is: absorbance = (slope) * concentration + y-intercept.
Now, let's use the provided information to find the concentration of [FeSal]+ in solution B:
Given:
- Absorbance of solution B = 0.379
- Slope of the standard curve = 1517 M-1
- Y-intercept of the standard curve = 0.001
Using the equation of the standard curve, we can rearrange it to solve for concentration:
absorbance = (slope) * concentration + y-intercept
0.379 = (1517 M-1) * concentration + 0.001
0.378 = 1517 * concentration
Concentration = 0.378 / 1517
Concentration = 2.492 x 10^-4 M
Now that we have the concentration of [FeSal]+ in solution B (2.492 x 10^-4 M), we can find the number of moles in a given volume.
Given:
- Volume of solution B = 50.00 mL
Number of moles = Concentration * Volume
Number of moles = (2.492 x 10^-4 M) * (50.00 mL) / 1000 (to convert mL to L)
Number of moles = 1.246 x 10^-5 moles
Therefore, there are 1.246 x 10^-5 moles of [FeSal]+ in the 50.00 mL of solution B.