This experiment is designed to give an induction to absorption spectroscopy with

Question

This experiment is designed to give an induction to absorption spectroscopy with the use of a Spectronic 20. The student will prepare a series of standard solutions by practicing dilution and pipetting techniques. Ultimately, the student will generate a calibration curve used to determine the concentration of an unknown solution. Calculate the molarity of a solution made by dissolving 4.8139 g of CoCl_2 middot 6H_2O in 100 mL of water. Calculate the molarity of a solution made by taking 1.0 mL of the solution from question 1 and diluting to 10.0 mL. Why must the 100% transmittance be reset on a Spectronic 20

Explanation / Answer

1. Molar mass of CoCl2.6H2O = 237.93 g/mol.

No. of moles = mass/ molar mass = 4.8319/237.93 mol

= 0.02031 moles

Volume of soln in litres = 0.1 litres

Molarity = No.of moles of solute/ vol of soln in litres = 0.02031/0.1

= 0.2031 M

2. If we take 1ml of the solution of above molarity then no of moles of solute in 1 ml = Molarity × Volume in litres

= 0.2031 × 10-3 moles.

This solute is now diluted to 10 ml solution.

Therefore Molarity = No of moles solute/ Vol of soln in litres

= 0.2031 × 10-3/ 0.01 = 0.02031M.

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