Answer:
Ferric ions left in the solution at equilibrium is
.
Explanation:
Moles of ferric nitrate in 0.700 L = n
Volume of the solution = V = 0.700 L
Molarity of ferric nitrate = M = 0.00150 M
![n=M\times V=0.00150 M\times 0.700 L=0.00105 mol](https://tex.z-dn.net/?f=n%3DM%5Ctimes%20V%3D0.00150%20M%5Ctimes%200.700%20L%3D0.00105%20mol)
Moles of potassium thiocyanate in 0.700 L = n'
Volume of the potassium thiocyanate solution = V' = 0.700 L
Molarity of potassium thiocyanate = M' = 0.200 M
![n'=M'\times V'=0.200 M\times 0.700 L=0.140 mol](https://tex.z-dn.net/?f=n%27%3DM%27%5Ctimes%20V%27%3D0.200%20M%5Ctimes%200.700%20L%3D0.140%20mol)
Molarity of ferric ions after mixing :
1 mol of ferric nitrate gives 1 mol of ferric ions.Then 0.00105 mol ferric nitrate will :
Moles of ferric ions = 0.00105 mol
![M_1=\frac{0.00105 mol}{0.700 L+0.700 L}=0.00075 M](https://tex.z-dn.net/?f=M_1%3D%5Cfrac%7B0.00105%20mol%7D%7B0.700%20L%2B0.700%20L%7D%3D0.00075%20M)
Molarity of thiocyanate ions after mixing :
1 mol of potassium thiocyanate gives 1 mol of thiocyanate ions.Then 0.140 mol potassium thiocyanate will give:
Moles of thiocyanate ions = 0.140 mol
![M_2=\frac{0.140 mol}{0.700 L+0.700 L}=0.1 M](https://tex.z-dn.net/?f=M_2%3D%5Cfrac%7B0.140%20mol%7D%7B0.700%20L%2B0.700%20L%7D%3D0.1%20M)
Complex equation:
![Fe^{3+}+SCN^-\rightleftharpoons [Fe(SCN)]^{2+}](https://tex.z-dn.net/?f=Fe%5E%7B3%2B%7D%2BSCN%5E-%5Crightleftharpoons%20%5BFe%28SCN%29%5D%5E%7B2%2B%7D)
0.00075 M 0.1 M 0
At equilibrium:
(0.00075 M -x) (0.1 M-x) x
The formation constant of the given complex =![K_f=8.9\times 10^2](https://tex.z-dn.net/?f=K_f%3D8.9%5Ctimes%2010%5E2)
![K_f=\frac{[[Fe(SCN)]^{2+}]}{[[Fe^{3+}]][SCN^{-}]}](https://tex.z-dn.net/?f=K_f%3D%5Cfrac%7B%5B%5BFe%28SCN%29%5D%5E%7B2%2B%7D%5D%7D%7B%5B%5BFe%5E%7B3%2B%7D%5D%5D%5BSCN%5E%7B-%7D%5D%7D)
![8.9\times 10^2=\frac{x}{(0.00075 M -x)\times (0.1 M-x)}](https://tex.z-dn.net/?f=8.9%5Ctimes%2010%5E2%3D%5Cfrac%7Bx%7D%7B%280.00075%20M%20-x%29%5Ctimes%20%280.1%20M-x%29%7D)
Solving for x:
x = 0.000742 M
Ferric ions left in the solution at equilibrium :
= (0.00075 M -x) = (0.00075 M - 0.000742 M)= ![8.0\times 10^{-6} M](https://tex.z-dn.net/?f=8.0%5Ctimes%2010%5E%7B-6%7D%20M)