Question

Two molecules X and Y are mixed into a solution. To determine the concentration (CX and CY) of each of these molecules in the solution, you measure the absorbance of the mixture at two wavelengths (260 nm and 340 nm). The light path is l=1 cm Based on the data contained in the table below, calculate the numerical values of CX and CY expressed in µmol.L-1 . Show your calculations. (6 pts) Hint: Each type of molecules contributes independently to the overall absorption. For example: A260 (absorbance of the mixture) = A260X (absorbance of X) + A260Y (absorbance of Y) with A260 X = l x (ex260 CX) and A260 Y = l x (eY260 CY) with l = light path

wavelength | 260 nm | 340nm |

absorbance | 260=1.17 | A340 = 0.189 |

ex (m2 /mol) | ex260 = 1.3 x 103 | ex340 = 0 |

eY (m2 /mol) | eY260 = 1.5 x 103 | eY340 = 6.3 x 102 |

Answer #1

we know that A=CT

A_{260}=A_{260x} +A_{260y}

A260 =(1x ex_{260} x Cx)+ (1x ey_{260} x Cy)

ex nd ey we need to convert in cm2/mol

ex=1.3x107 cm2/mol, ey= 1.5x107 cm2/mol

substute the values in above equation

1.17=1.3x107xCx +1.5x107x Cy 1

similarly A340=A_{340x} +A_{340y}

0.189= 0+6.3x106x Cy

Cy=(0.189/6.3x106)

Cy=0.03x10-6 mol/L

**Cy=0.03 mol/L**

substitute Cy value in equation one we get Cx

1.17= 1.3x107xCx+1.5x107x0.03x10-6

1.17=1.3x107xCx+0.45

1.3x107Cx=0.72

Cx=5.54x10-8 mol/L

**Cx=0.055 mol/L**

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