CHEM 103 Study Guide - Comprehensive Midterm Guide: Ethylamine, Aniline, Thermodynamics

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5 Oct 2016

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Sample calculations : suppose that we prepare a mixture by mixing 2. 00 10. 2+ ion is formed by the complexation reaction. Its concentration at equilibrium is found to be 2. 50 10. M. our problem is to find kc for the reaction from this information. = concentration of stock solution initial concentration of fe. = 0. 00 m, because we did not add any to the mixture. , must have decreased by the same amount. This is due to the 1:1 stoichiometric ratio; one mole each of fe. 3+ and scn are used up for every one mole of fescn. Once the equilibrium concentrations of all the reactants and products are known, they can be substituted into the equilibrium expression to determine kc. Your experimental result for kc may be different from this result, because the data in this example were obtained at a different temperature.

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1. A student mixes 5.00 mL 2.00 X 10~3 M Fe(NO3)3 with 5.00 mL 2.00 X 10-3 M KSCN. She finds that in the equilibrium mixture the concentration of FeSCN2+ is 1.20 X 10-4 M. Find Kc for the reaction Fe3+(aq) + SCN-(aq) (arrows) FeSCN2 (aq).Step 1. Find the number of moles Fe3+ and SCN- initially present. (Use Eq. 3.)________moles Fe3+; ________moles SCN-Step 2. How many moles FeSCN2+ are in the mixture at equilibrium? What is the volume of the equilibrium mixture? (Use Eq. 3.).__________mL; ________moles FeSCN2+How many moles of Fe3+ and SCN~ are used up in making the FeSCN2"1"?.__________moles Fe3+; _________moles SCN-Step 3. How many moles of Fe3+ and SCN- remain hi the solution at equilibrium? (Use Eq. 4 and the results of Steps 1 and 2.)_______molesFe3+ ________molesSCN-Step 4. What are the concentrations of Fe3*, SCN-, and FeSCN2+ at equilibrium? What is the volume of the equilibrium mixture? (Use Eq. 3 and the results of Step 3.)[Fe3+] = _______M; [SCN-] =_________ M; [FeSCN2*] = _________MmLStep 5. What is the value of Kc for the reaction? (Use Eq. 2 and the results of Step 4.)Kc=_________

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Need Help on how to find the answers. I don't think mine are right.

A student prepared the following mixtures and measured the time each took to react. Calculate the average time for each mixture (in seconds).

Mixture	Vol. of 4.0 M acetone (mL)	Vol. of 1.0 M HCl (mL)	Vol. of 0.0050 M I₂ (mL)	Vol. of H₂O (mL)	Time for Trial 1	Time for Trial 2	Average time (s)
1	10	10	10	20	249	251	250
2	20	10	10	10	123	125	124
3	10	20	10	10	121	124	122.5
4	10	10	5	25	124	126	125

To complete the following table:

Determine the initial concentration (molarity) of each reagent using the equation:

The M_stock and V_stock for each reagent are given in problem 1. The total volume is 50 mL for each trial.

Calculate the rate of the reaction using the equation

Mixture	[Acetone], M	[H⁺], M	[I₂]₀, M	Rate
1	0.80	0.20	0.0010
2
3
4

Determine the rate law by finding the orders of the reaction (m, n, and p).

Rate = k[acetone]^m[H⁺]ⁿ[I₂]^p

Use the rate law determined in problem 3 to calculate the rate constant, k for each mixture. Find the average rate constant.

Mixture	1	2	3	4	Average
k

We will now consider reaction mixture 5. Calculate the molar concentrations of each reactant as done in problem 2.

	4.0 M Acetone	1.0 M HCl	0.0050 M I₂	H₂O
Volume (mL)	10.0	5.0	10.0	25.0
Concentration (M)				--------------

Use the concentrations for Mixture 5 you just calculated, along with the orders of the reaction (m, n, and p, from problem 3), and the average rate constant (problem 4), to solve Eq. 2 for rate. This is a prediction of how long it will take for the I₂ color to disappear from your mixture.

Rate = k[acetone]^m[H⁺]ⁿ[I₂]^p

Predicted Rate:____________________

To find the predicted time, recall. Use the rate from problem 5 and the molar concentration of [I₂]₀ from problem 5 to solve for the predicted time.

Find concentration of [FeSCN+2] for tetssttubes 1, 2, and 3.

Find the equilibrium concentration of [FeSCN+2] for test tubes 4, 5, and 6.

Find Kc for test tube 4, 5, and 6.

Show work for all values found from test tube 4.

CHEM 103 Study Guide - Comprehensive Midterm Guide: Ethylamine, Aniline, Thermodynamics

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