analytical chemistry

Question 6: Molecular (UV/VIS) spectrophotometry

a) A solution containing 0.010 M of a substance A gives an absorbance equal to 0.053. Another solution containing 0.020 M of a substance B gives an absorbance equal to 0.037. Both solutions contain the same solvent. What transmittance is obtained for a mixture consisting of 10.0 ml of the first solution and 20.0 ml of the second solution? All measurements are made at the same wavelength.

b) If you do not close the door to the cuvette holder in a UV/VIS instrument properly, it may happen that you get incorrect absorbance values. Describe what causes such errors and also explain whether it is samples with high or low absorbance that are most affected. Motivate!