Simultaneous Analysis of a Two-Component Mixture

Analytical Chemistry

2/25/13

Experiment 4: Simultaneous Analysis of a Two-Component Mixture

Objective

The main purpose of this experiment was to study the absorption properties of a mixture of chromium (III) nitrate and cobalt (II) nitrate and use those measurements to determine an unknown. When a solution of two or more light-absorbing substances is made, the presence of the other will not affect the light absorbing properties of the other components. The absorption of light is additive and the total will be equal to the sum of the individual substances. The absorbance of the mixture can be compared to the sum of the absorbances of pure solutions of each substance that have the same concentration. To achieve this result both the absorbance of the mixture and the molar absorptivities of each of the substances must be measured at a minimum of as many wavelengths as there are substances. The results will make n equations with n unknowns which can then be solved. A manipulation of Beer’s law gave the equation for the linear regression, shown below.

A linear regression plot of Am/AXs vs AYs/AXs will yield a straight line with a slope of [Y]/[Y]s and an intercept of [X]/[X]s. The concentrations of X and Y in the unknown mixture can be determined from the slope and intercept values.

Data

Table 1: Absorbance readings per solution

| Absorbance |

| 500 | 510 | 520 | 530 | 540 | 550 | 560 | 570 | 580 | 590 | 600 |

A | 0.3876 | 0.4121 | 0.3952 | 0.3413 | 0.2602 | 0.1795 | 0.1147 | 0.0691 | 0.0447 | 0.0348 | 0.0314 |

B | 0.0927 | 0.1180 | 0.1531 | 0.1948 | 0.2395 | 0.2795 | 0.3093 | 0.3253 | 0.3257 | 0.3122 | 0.2856 |

C | 0.4880 | 0.5361 | 0.5516 | 0.5369 | 0.4963 | 0.4545 | 0.4193 | 0.3895 | 0.3652 | 0.3414 | 0.3104 |

D | 0.4323 | 0.4811 | 0.5071 | 0.5118 | 0.4963 | 0.4779 | 0.4614 | 0.4438 | 0.4240 | 0.3992 | 0.3636 |

| Absorbance |

Solutions | 400 | 410 | 420 | 430 | 440 | 450 | 460 | 470 | 480 | 490 |

A | 0.0007 | 0.0090 | 0.0261 |...