Question

Pipene a sample into a well on a microplate and get an absorbance of 0.25, and your partner pipettes the same sample into the same plate and gets an absorbance of 0.32. Assume une microplate is clean and a blank well has been referenced properly. What could account for the difference in absorption readings? (Please reference Beer's Law in your answer.) 6. You are tasked with preparing 250 mL of a 100 mM sodium phosphate buffer (pKa - 7.21) containing 0.2 M sodium chloride at a pH of 7.4, a common buffer known as phosphate- buffered saline (PBS). Complete the following table and describe the steps you would use to prepare the buffer. Mass (g) Component NaH2PO4 H2O Na2HPO4-2H2O NaCl Concentration (MM) MW (g/mol) 137.99 177.99 200 58.44

Answer 1

Component	Concentration (mM)	MW(g/mol)	Mass(g)
NaH2PO4.H2O	22.6	137.99	0.779
Na2HPO4.2H2O	77.4	177.99	3.444
NaCl	200	58.44	2.922

The buffering range for the buffer constructed in question 6 is from 6.4 to 8.4

From Beer's law, me = Mola Absorption - Ecl. bt where, & = Molar absorption co-efficient ca molas concentration V = optical path Length . As you and your friend pipetted from same sample and measured the absorption with same microplate. Hence, it is only possible cause of different absorption, that due to different molar absorption co-efficient absorptivity ne molar constant is an intrinsic property of the species. It is a measure of how strongly a chemical species absorbs light at a given wavelength. absorption of you both are surement you and your used light of of absorbance. . Hence, the different trend is probably due to different wavelength for