Sapling Learning Poun of two ds (0.010 M compound A in solvent 100 The IR (infra

Question

Sapling Learning Poun of two ds (0.010 M compound A in solvent 100 The IR (infrared) 90 and b.010 M compound B in solvent) are shown to the right. The pathlength of the cell is 1.00 cm. Note that the y axis in the spectra is transmittance rather than absorption, so that the wavenumbers at which there is a dip in the curve correspond to absorption peaks. Dest 70 60 50 40 g A mixture of A and B in unknown concentrations £ gave a percent transmittance of 48.3% at 2976-30 on-land 41.9% at 3030 m-1. 3030 cm2976 m 20 10 Pure B 3040 Wavenumber 0.010 M A 0.010 MBUnknown 3030 on" | 35.0% 2976 ml | 76 0% what are the concentrations of A and B in the unknown sample? wavenumber (cm 93 0% 419% 42.0% 48.3% 0.008728 BItt 110.00782 o w M A M B O Te

Explanation / Answer

wave number (cm-1)

A

B

unknown

3030

0.456

0.0315

0.378

2976

0.119

0.377

0.316

Absorbance = A = E x b x C

wave number

A

B

3030

E = 45.6 M-cm-1

3.15 M-1 cm-1

2976

E = 11.9 M-1 cm-1

37.7 M-1 cm-1

0.378 = 45.6 A + 3.15 B ----------------------(1)

0.316 = 11.9 A + 37.7 B ---------------------(2)

by solving these two

A = 0.00788 M

B = 0.00589 M

wave number (cm-1)

A

B

unknown

3030

0.456

0.0315

0.378

2976

0.119

0.377

0.316

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