Chemical Reaction and Equilibrium Constant Expression
Ashley Silva
Lab 7: Three Stooges in Chemical Reactions
Objective: The purpose of this lab is to experimentally determine the equilibrium constant, Kc , for the following chemical reaction: Fe3+ (aq) + SCN-(aq) ↔FeSCN2+(aq)
Background Information: A system is at equilibrium when the rate of the forward reaction is the same as the rate of the reverse reaction. There is no change in concentration for the reactants or products at chemical equilibrium. When the system is disturbed there is a shift to reestablish equilibrium explained by Le Chatelier’s Principle. It states that when a stress is places on a system at equilibrium the system will shift to relieve the stress and reestablish equilibrium. Forms of stress include change in concentration, change in pressure, and change in volume.
Procedure:
1. Prepare three different solutions, each solution #1: 3mg Fe, 7mg SCN totaling 10 mL, using any amount of Fe3+ and SCN2+ #2: 4mg Fe, 6mg SCN and place each in separate cuvettes. #3: 5mg Fe, 5mg SCN
2. Determine the initial concentration of each ion.
3. Use the dilution formula ( M1V1=M2V2) to determine #1 abs = 0.320 @ 10 sec. the concentration of Fe3+ and SCN2+ in each mixture. #2 abs = 0.331 @ 4 sec.
4. Then use the spectrophotometer to measure the #3 abs = 0.334 @ 27 sec. absorbance of each solution.
5. Calculate the concentration of FeSCN2+ in each sample using absorbance (C= A/Eb)
6. Calculate [Fe+3] and [SCN] using the RICE table.
7. Calculate the concentration of each
Lab 7: Three Stooges in Chemical Reactions
Objective: The purpose of this lab is to experimentally determine the equilibrium constant, Kc , for the following chemical reaction: Fe3+ (aq) + SCN-(aq) ↔FeSCN2+(aq)
Background Information: A system is at equilibrium when the rate of the forward reaction is the same as the rate of the reverse reaction. There is no change in concentration for the reactants or products at chemical equilibrium. When the system is disturbed there is a shift to reestablish equilibrium explained by Le Chatelier’s Principle. It states that when a stress is places on a system at equilibrium the system will shift to relieve the stress and reestablish equilibrium. Forms of stress include change in concentration, change in pressure, and change in volume.
Procedure:
1. Prepare three different solutions, each solution #1: 3mg Fe, 7mg SCN totaling 10 mL, using any amount of Fe3+ and SCN2+ #2: 4mg Fe, 6mg SCN and place each in separate cuvettes. #3: 5mg Fe, 5mg SCN
2. Determine the initial concentration of each ion.
3. Use the dilution formula ( M1V1=M2V2) to determine #1 abs = 0.320 @ 10 sec. the concentration of Fe3+ and SCN2+ in each mixture. #2 abs = 0.331 @ 4 sec.
4. Then use the spectrophotometer to measure the #3 abs = 0.334 @ 27 sec. absorbance of each solution.
5. Calculate the concentration of FeSCN2+ in each sample using absorbance (C= A/Eb)
6. Calculate [Fe+3] and [SCN] using the RICE table.
7. Calculate the concentration of each