How would the absorbance of the standard solution have been affected if 0.00050 M NaSCN had been used in place of 0.00040 M NaSCN?
If iron(III) was the limiting reagent, would there be any difference in A?
the limiting reagent is the SCN
If I am determining the amount of iron(III) with thiocyanate, then I want iron to be the limiting reagent. If I am determining SCN^-, I want the limiting reagent to be SCN^-. Of course you may be doing something different but your post provides none of that information.
To determine how the absorbance of the standard solution would be affected by using a different concentration of NaSCN, we need to understand the relationship between absorbance and concentration.
In a spectrophotometric analysis, absorbance (A) is directly proportional to the concentration (c) of the absorbing species according to the Beer-Lambert Law:
A = εlc
where A is the absorbance, ε is the molar absorptivity (a constant that depends on the absorbing species and the wavelength of light), l is the path length of the solution, and c is the concentration.
In this case, we are comparing two concentrations of NaSCN: 0.00040 M and 0.00050 M.
Assuming that the path length (l) and the molar absorptivity (ε) are constant, we can use the Beer-Lambert Law to determine the relationship between the two absorbances.
Let's call the absorbance with 0.00040 M NaSCN "A1" and the absorbance with 0.00050 M NaSCN "A2".
A1 = εl * 0.00040 M
A2 = εl * 0.00050 M
To compare the two absorbances, we can divide A2 by A1:
A2/A1 = (εl * 0.00050 M) / (εl * 0.00040 M)
Note that the path length and molar absorptivity cancel out, leaving us with a ratio of the two concentrations:
A2/A1 = 0.00050 M / 0.00040 M
To simplify the ratio, we can divide both the numerator and denominator by 0.00040 M:
A2/A1 = (0.00050 M / 0.00040 M) / (0.00040 M / 0.00040 M)
= (0.00050 M / 0.00040 M) / 1
Simplifying further, we can divide 0.00050 M by 0.00040 M:
A2/A1 = 1.25
Therefore, if 0.00050 M NaSCN were used instead of 0.00040 M NaSCN, the absorbance of the standard solution would be 1.25 times higher.