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

Answer 1

0.200 M

Step-by-step explanation:

Step 1: Given data

• Mass of CoCl₂ (m): 2.60 g

• Molar mass of CoCl₂ (M): 130. g/mol

• Volume of solution (V): 100. mL (0.100 L)

Step 2: Calculate the moles (n) of CoCl₂ (solute)

We will use the following expression.

n = m / M

n = 2.60 g / (130. g/mol) = 0.0200 mol

Step 3: Calculate the molar concentration of the solution

Molarity is equal to the moles of solute divided by the liters of solution.

M = n/V

M = 0.0200 mol/0.100 L = 0.200 M