Cobalt and nickel can be simultaneously determined by formation of their coloured complexes with 8-quinolinol in solution. Molar extinction coefficients are: εCo = 3529, and εNi = 3228 cm-1 M-1 at 365 nm; and εCo = 428.9 and εNi = 0 cm-1 M-1 at 700 nm. Calculate the concentrations of nickel and cobalt in a solution which has absorbances of 0.725 at 365 nm and 0.0710 at 700 nm in a 1 cm cell.
DrBob222 Please work your magic!
Sorry I was late getting back. I was typing in the answer, I received a call to go to lunch, I had to RIGHT THEN, just now returned. So here goes. I can write that epsilon so I'll use e.
A @ 725 nm = eCo*Ccobalt + eNi*CNickel
A @ 700 nm = eCo*Ccobalt
Calculate C Cobalt at 700, plug into C Cobalt at 725 and solve for C Ni at 725.
To calculate the concentrations of nickel and cobalt in the given solution, we can use the Beer-Lambert Law. The Beer-Lambert Law states that the absorbance of a sample is directly proportional to the concentration of the absorbing species, the path length of the sample, and the molar extinction coefficient of the species at a particular wavelength.
The formula for the Beer-Lambert Law is:
A = εlc
Where:
A = Absorbance
ε = Molar extinction coefficient
l = Path length
c = Concentration
First, let's calculate the concentrations of cobalt and nickel using the absorbance at 365 nm.
For cobalt (Co):
A = εCo * l * cCo
Given:
A = 0.725 (absorbance at 365 nm)
εCo = 3529 cm-1 M-1
l = 1 cm
Substituting the given values into the formula:
0.725 = 3529 * 1 * cCo
cCo = 0.725 / 3529
cCo ≈ 0.0002056 M
For nickel (Ni):
A = εNi * l * cNi
Given:
A = 0.725 (absorbance at 365 nm)
εNi = 3228 cm-1 M-1
l = 1 cm
Substituting the given values into the formula:
0.725 = 3228 * 1 * cNi
cNi = 0.725 / 3228
cNi ≈ 0.0002248 M
Next, let's calculate the concentrations of cobalt and nickel using the absorbance at 700 nm.
For cobalt (Co):
A = εCo * l * cCo
Given:
A = 0.0710 (absorbance at 700 nm)
εCo = 428.9 cm-1 M-1
l = 1 cm
Substituting the given values into the formula:
0.0710 = 428.9 * 1 * cCo
cCo = 0.0710 / 428.9
cCo ≈ 0.0001657 M
For nickel (Ni):
A = εNi * l * cNi
Given:
A = 0.0710 (absorbance at 700 nm)
εNi = 0 cm-1 M-1 (As stated, nickel has no molar extinction coefficient at 700 nm)
l = 1 cm
Substituting the given values into the formula:
0.0710 = 0 * 1 * cNi
cNi = 0.0710 / 0
Here, we can observe that nickel has no molar extinction coefficient at 700 nm (εNi = 0). Therefore, we cannot determine the concentration of nickel using the absorbance at this wavelength.
In conclusion, the concentration of cobalt in the solution is approximately 0.0002056 M, and the concentration of nickel cannot be determined since its molar extinction coefficient at 700 nm is 0.