Question

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

Answer 1

Answer:

A

Explanation:

2.60 g of CoCl2 was dissolved in water to make 100 mL of solution.

Number of moles of CoCl2 dissolved = mass/molar mass

                                = 2.60/130

                                   = 0.02 mole

Molar concentration of solutions = number of moles/volume (dm3)

                          = 0.02/0.1

                            = 0.200 M

Hence, the molar concentration of thesolution is 0.200 molar.

Correct option = A