Question

Fe³⁺ (aq) +KSCN(s)->FeSCN²⁺(aq)+K⁺(aq) To determine the moles of Fe3+(aq) in a 100mL sample of an unknown solution, excess KSCN(s) is added to convert all the Fe3+(aq) into the dark red species, FeSCN2+(aq), as represented by the equation above. The absorbance of FeSCN2+(aq) a different concentration is shown in the graph to the right. a) If the absorbance of the mixture is 0.20 at 453 nm, how many moles of Fe3+(aq) were present in the 100 mL sample? (Assume that any volume change due to adding the KSCN(s) is negligible. b) If the absorbance of the mixture is 0.40 at 453 nm, how many moles of Fe3+(aq) were present in the 100 mL sample? (Assume that any volume change due to adding the KSCN(s) is negligible.

Answer 1

To determine the moles of Fe3+(aq) in a 100mL sample of the unknown solution, we can use the Beer-Lambert Law. By plugging in the given absorbance values and the molar absorptivity, we can calculate the concentration and convert it to moles.

Step-by-step explanation:

To determine the moles of Fe3+(aq) in a 100mL sample of the unknown solution, we can use the Beer-Lambert Law. The Beer-Lambert Law states that the absorbance of a solution is directly proportional to the concentration of the absorbing species.

In this case, the absorbance of FeSCN2+(aq) is given as 0.20 and 0.40 at 453 nm.

Using the equation A = εlc, where A is the absorbance, ε is the molar absorptivity, l is the path length (which is usually 1 cm), and c is the concentration, we can rearrange the equation to solve for c.

In this case, we know the absorbance (A) is 0.20 or 0.40, the path length (l) is 1 cm, and the molar absorptivity (ε) can be determined experimentally. By plugging in those values, we can solve for the concentration (c), which represents the moles of Fe3+ in the 100 mL sample.

Therefore, the moles of Fe3+(aq) present in the 100 mL sample can be calculated using the absorbance and the molar absorptivity of FeSCN2+(aq) at 453 nm.