Question

Pure solid NaH2PO4 is dissolved in distilled water, making 100.00 ml of solution. 10.00ml of this solution is diluted to 100.00 ml to prepare the original phosphate standard solution. Three working standard solutions are made from this by pipetting 0.8ml, 1.5ml and 3.0 ml of the original standard solution into 100.00 ml volumetric flasks. Acid and molybdate reagent are added and the solutions are diluted to 100.00 ml. You may assume that all these absorbance measurements have already been corrected for any blank absorbance. The absorbance of each is measured in the spectrophotometer. Mass of NaH2PO4 (mg) 512.2

Absorbance Standard 1 (0.8 ml) 0.1922

Standard 2 (1.5 ml) 0.3604

Standard 3 (3.0 ml) 0.7209

Calculate the following:

Concentration of original phosphate standard (mM)

Concentration of Standard 1(mM)

Concentration of standard 2(mM)

Concentration of standard 3 (mM)

slope of calibraton line

A 10.00 ml volume of soft drink is treated with acid and molybdate and diluted to 100.00 ml. Its absorbance is measured. From the following data, calculate the concentration of phosphate in the soft drink (mM).

Sample absorbance                  0.2255

Slope of the calibration line: 5.47      

Answer 1