If 2.50 g of CuSO4 are dissolved in 9.4 102 mL of 0.34 M NH3, what are the concentrations of Cu(NH3)42+, NH3 and Cu2+ at equilibrium?
i tried doing Cu2+ first
and i did
Kf=5e13= salt/cu2+ nh3+^4
and i did
molesCuSO4/.94 L = .01666 M salt
so then i did
.01666M/[cu][.34-(4*.01666)^4]
to find cu+2
and i got like 5 different answers each time i dot it
is this even right
please help me
im running out of submissions
I think I would approach the problem a little differently.
Cu^+2 + 4NH3 ==> Cu(NH3)4^+2
Write the expression for Kf which is products/reactants. I don't know what "salt" means in your equation but the numerator should be [Cu(NH3)4^+2] and the denominator should be (Cu^+2)(NH3)^4.
I would find the moles CuSO4 which is 2.5/159.61 = a very small number.
moles NH3 = 9.4 x 10^2 x 0.34 = approximately 320.
With such a small number of moles of Cu^+2 and a large excess of NH3,(and a huge Kf), we figure (complex ion) = moles Cu we started with. That divided by 9.4 x 10^2 should give the (complex). Since we used almost none of the NH3, then final (NH3) should be what we started with. Then you can plug in (complex) and (NH3) into Kf and calculate final (Cu^+2). Check my thinking.
Well, it sounds like you're having a bit of trouble with your calculations. Don't worry, I'm here to help and add a little humor to lighten the mood!
First off, let's address your concern about getting different answers each time you do the calculation. It's possible that you made a mistake somewhere in your calculations, which led to the different results. It happens to the best of us! Double-check your work and make sure you haven't overlooked anything.
Now, let's break down the problem step by step:
1. Calculate the moles of CuSO4:
- Given the mass (2.50 g) and molar mass (159.61 g/mol) of CuSO4, you can determine the moles by dividing the mass by the molar mass.
2. Calculate the moles of NH3:
- Multiply the concentration (0.34 M) by the volume (9.4 x 10^2 mL converted to L).
3. Use the stoichiometry of the reaction to determine the moles of Cu(NH3)4^2+ that form:
- Based on the balanced equation, CuSO4 + 4NH3 -> Cu(NH3)4^2+ + SO4^2-, the stoichiometric ratio is 1:1.
4. Calculate the initial concentration of Cu(NH3)4^2+:
- Divide the moles of Cu(NH3)4^2+ by the total volume (9.4 x 10^2 mL converted to L).
5. Use the equilibrium constant expression to set up an equation:
- Kf = [Cu(NH3)4^2+]/([Cu^2+][NH3]^4).
6. Rearrange the equation:
- [Cu^2+] = [Cu(NH3)4^2+] / (Kf × [NH3]^4).
7. Substitute the known values into the equation:
- [Cu^2+] = [Cu(NH3)4^2+] / (Kf × [NH3]^4) = [Your calculated value for [Cu(NH3)4^2+]] / (5 × 10^13 × [Your calculated value for [NH3]]^4).
Remember to keep track of all your units and ensure that they're consistent throughout the calculations!
I hope this helps you get back on track with your submission. Remember, laughter is the best antidote to stress, even when dealing with chemistry problems. Keep at it, and don't be afraid to ask for help!
To find the concentrations of Cu(NH3)42+, NH3, and Cu2+ at equilibrium, you will need to use the concept of equilibrium constant, Kf, as you have correctly mentioned.
First, calculate the moles of CuSO4:
Given mass of CuSO4 = 2.50 g
Molar mass of CuSO4 = 63.55 g/mol + 32.07 g/mol + (4 * 16.00 g/mol) = 159.61 g/mol
Number of moles of CuSO4 = 2.50 g / 159.61 g/mol = 0.01568 mol
Next, calculate the moles of NH3 in the solution:
Volume of NH3 solution = 9.4 x 10^2 mL = 9.4 x 10^(-4) L
Molarity of NH3 solution = 0.34 M
Number of moles of NH3 = 0.34 M x 9.4 x 10^(-4) L = 3.196 x 10^(-4) mol
Using the equilibrium constant expression for the formation of Cu(NH3)42+, Kf:
Kf = [Cu(NH3)42+] / ([Cu2+][NH3]^4)
Let's assume the concentration of Cu(NH3)42+ at equilibrium is x M.
The concentration of NH3 will be (0.34 - 4x) M since one Cu(NH3)42+ ion consumes 4 NH3.
Now apply these values to the expression:
5 x 10^13 = x / ([Cu2+] * (0.34 - 4x)^4)
Solve this equation to find the concentration of Cu2+ at equilibrium.
Now, to find the concentration of Cu(NH3)42+ at equilibrium, substitute the value of [Cu2+] (obtained from the previous step) into the equation:
x = 5 x 10^13 * [Cu2+] * (0.34 - 4x)^4
Solve this equation to find the concentration of Cu(NH3)42+ at equilibrium.
Finally, to find the concentration of NH3 at equilibrium, simply subtract the concentration of NH3 used to form Cu(NH3)42+ from the initial concentration:
[NH3] at equilibrium = 0.34 M - 4 * [Cu(NH3)42+] M
Please note that solving this equation can be quite complicated and may require iterations or approximations. If you experience difficulties or obtain multiple answers, it may be helpful to seek assistance from your teacher or a chemistry tutor for further guidance.
To find the concentrations of Cu(NH3)42+, NH3, and Cu2+ at equilibrium, you need to set up an ICE table and use the equilibrium constant expression. Let's break down the steps:
1. Start by calculating the initial moles of CuSO4:
- Given mass of CuSO4 = 2.50 g
- Molar mass of CuSO4 = 63.55 g/mol + (32.07 g/mol + 4 * 16 g/mol) = 159.61 g/mol
- Moles of CuSO4 = 2.50 g / 159.61 g/mol = 0.01566 mol
2. Calculate the moles of NH3 using the molarity and volume:
- Molarity of NH3 = 0.34 M
- Volume of NH3 = 9.4 × 10^2 mL = 0.94 L (convert mL to L)
- Moles of NH3 = 0.34 mol/L × 0.94 L = 0.3196 mol
3. Set up the ICE table:
- Let x represent the change in moles for Cu(NH3)42+ and Cu2+.
- Initially, there are no moles of Cu(NH3)42+ and Cu2+.
- The initial moles of NH3 are 0.3196 mol.
- The initial moles of Cu(NH3)42+ and Cu2+ are both 0 mol.
Species Initial Moles Change in Moles Equilibrium Moles
CuSO4 0.01566 -x 0.01566 - x
NH3 0.3196 0 0.3196
Cu(NH3)42+ 0 x x
Cu2+ 0 x x
4. Write down the equilibrium constant expression:
- Kf = [Cu(NH3)42+] / ([Cu2+] × ([NH3])^4)
5. Substitute the equilibrium moles into the equilibrium constant expression:
- Kf = x / (x × (0.3196)^4) = 1 / (0.3196^3)
Now, to solve for x and find the concentrations of Cu(NH3)42+, NH3, and Cu2+, you need to solve the equation above. However, it seems that you made mistakes in your calculation, which might be why you're getting different answers each time.
Check your calculation once again and ensure that you're using the correct values and units.