Simultaneous Spectrophotometric Quantitation of CuII and NiII

1. Simultaneous Spectrophotometric Quantitation of Cu(II) and Ni(II) Experiment 9

2. Purpose Absorbance � Single Analyte Absorbance � Multiple Analyte Solving unknown concentrations Procedure Safety Concerns Waste What to turn in Experiment 10 reminder Outline

3. The purpose of this lab is to demonstrate the additive property of absorbance. The molar absorptivity (e) values for both Cu(II) and Ni(II) will be found at two analytical wavelengths by measuring the absorbance of both ions in solutions of known concentration. The two analytical wavelengths will then be utilized to find the concentrations of both Cu(II) and Ni(II) in an unknown mixture. Purpose

4. For a single analyte, we can use the Beer-Lambert Law: Abs = e b c to determine any one of the variables, given that three of them are already known. Since molar absorptivity (e ) is the same for a given compound (x), regardless of concentration, at a given wavelength, we can clarify Beer�s Law terms: A?1 = e?1x b [x] Given that the path length (b) through our cuvets is 1.445 cm, we can define a new variable k?1x = e?1x b to simplify calculations and modify Beer�s Law accordingly: A?1 = k?1x [x] After you make up your solutions today, you will simply use this modified Beer�s Law to determine the molar absorptivity (k?1x ) of each solution at a given wavelength. The average k value for each set of solutions at each wavelength is calculated and used to solve for unknown concentrations. Absorbance � Beer�s Law

5. For multiple analytes we exploit the additive property of absorbance: AbsT = Abs1 + Abs2 + ... The same number of wavelengths are used as number of analytes that are analyzed. Therefore, in two analytes, we use: A?1 = e?1x b [x] + e?1y b [y]; Define k?1x = e?1x b and k?1y = e?1y b; So A?1 = k?1x [x] + k?1y [y] A?2 = e?2x b [x] + e?2y b [y]; Define k?2x = e?2x b and k?2y = e?2y b; So A?2 = k?2x [x] + k?2y [y] Absorbance is Additive

6. Beer�s Law states: A?1 = k?1x [x] + k?1y [y] At 395 nm, this equation becomes: A395 = k395Ni(II)[Ni2+] + k395Cu(II)[Cu2+] = k395 [Ni2+] + 0 To solve for [Ni2+] in our unknown solution: [Ni2+] = At 395 nm, only Ni2+ absorbs