A student uses visible spectrophotometry to determine the concentration of CoCl2(aq) in a sample solution. First the student prepares a set of CoCl2(aq) solutions of known concentration. Then the student uses a spectrophotometer to determine the absorbance of each of the standard solutions at a wavelength of 510nm and constructs a standard curve. Finally, the student determines the absorbance of the sample of unknown concentration.

The original solution used to make the solutions for the standard curve was prepared by dissolving 2.60g of CoCl2 (molar mass 130.g/mol) in enough water to make 100.mL of solution. What is the molar concentration of the solution?

A) 0.200 mol
B) 0.500 mol
C) 1.00 mol
D) 5.00 mol

A student prepared a solution used to make the solutions for the standard curve by dissolving 2.60g of CoCl₂ (molar mass 130. g/mol) in enough water to make 100. mL of solution. The molar concentration of the solution is 2.00 M.

First, we will convert 2.60 g to moles of CoCl₂ using its molar mass (130. g/mol) as the conversion factor.

[tex]2.60 g \times \frac{1mol}{130. g} = 0.0200 mol[/tex]

0.0200 moles of CoCl₂ are in 100. mL (0.100 L) of solution. The molar concentration of the solution is:

[tex]M = \frac{0.200 mol}{0.100 L} = 2.00 M[/tex]

A student prepared a solution used to make the solutions for the standard curve by dissolving 2.60g of CoCl₂ (molar mass 130. g/mol) in enough water to make 100. mL of solution. The molar concentration of the solution is 2.00 M.

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