This is for a lab about determining the equilibrium constant.
Given: 5.00mL of .203M Fe(NO3)3 mixed with 100mL of .00205M KSCN in a .5M HNO3 solvent for both solutions. Resulting absorbance for solution is .315.
How can i find the total Fe, [Fe*] and SCN, [SCN*] in the system without determining equilibrium values of [FeSCN+2], [Fe+3], and [SCN-].
What i know so far is that:
Fe+3 + SCN- makes FeSCN+2
[Fe*] = [Fe+3] + [FeSCN+2]
[SCN*] = [SCN-] + [FeSCN+2]
Make an ICE chart.
Total Fe = moles Fe(NO3) = 5.00 mL x 0.203 M = ??millimoles Fe.
Total SCN = mL x M = 100 x 0.00205 = ??millimoles SCN
...............Fe^+3 + SCN^- ==> FeSCN^+2
initial......
change.......
equil........
One caution here. The ICE chart prepared as above is done with millimoles. Before you can use this to determine a Keq value, millimoles must be changed to M which = millimoles/TOTAL mL.
Total mL in this case is 105 mL.
To find the total concentration of Fe, [Fe*], and SCN, [SCN*], in the system without directly determining the equilibrium values of [FeSCN+2], [Fe+3], and [SCN-], you can use stoichiometry and the given information.
1. Calculate the moles of Fe(NO3)3:
Moles of Fe(NO3)3 = volume (in liters) × concentration (in mol/L) = (5.00 mL / 1000 mL/L) × 0.203 mol/L
2. Calculate the moles of KSCN:
Moles of KSCN = volume (in liters) × concentration (in mol/L) = (100 mL / 1000 mL/L) × 0.00205 mol/L
3. Using the balanced equation Fe+3 + SCN- → FeSCN+2, determine the stoichiometric ratio:
From the balanced equation, the stoichiometric ratio is 1:1 between Fe+3 and SCN-.
4. Since the total volume is 100 mL (from KSCN solution) + 5.00 mL (from Fe(NO3)3 solution), convert both moles of Fe(NO3)3 and moles of KSCN to their total concentrations in the final solution:
Total concentration of Fe = (moles of Fe(NO3)3) / (total volume in liters)
Total concentration of SCN = (moles of KSCN) / (total volume in liters)
5. Calculate the remaining concentration of FeSCN+2 based on absorbance:
The absorbance can be related to the concentration of FeSCN+2 using the Beer-Lambert Law: A = εcl, where A is the absorbance, ε is the molar absorptivity, c is the concentration, and l is the path length of the solution cell.
In this case, using the known absorbance value of 0.315, you can find the concentration of FeSCN+2.
Note: The molar absorptivity (ε) is specific to the system being studied and should be provided or determined separately.
Therefore, the total concentration of Fe ([Fe*]) in the system is the sum of the concentration of Fe(NO3)3 ([Fe+3]) and the remaining concentration of FeSCN+2. Similarly, the total concentration of SCN ([SCN*]) is the sum of the concentration of KSCN ([SCN-]) and the remaining concentration of FeSCN+2.
Remember to use appropriate units and conversions throughout the calculations.