Question

What is the concentration of an AlCl₃ solution if 150.0mL of the solution contains 250.0mg of Cl⁻ ion?

A) 1.41 x 10⁻¹ M
B) 3.75 x 10⁻² M
C) 1.57 x 10⁻² M
D) 4.70 x 10⁻² M

Answer 1

To calculate the concentration of the AlCl₃ solution, we convert the mass of Cl⁻ to grams, find the moles of Cl⁻, determine the moles of AlCl₃, and then divide by the volume in liters to get the molarity, which is 1.57 x 10⁻² M (Option C).

Step-by-step explanation:

To find the concentration of the AlCl₃ solution, we need to determine the number of moles of Cl⁻ ion present in the given mass and then use that to calculate the molarity of the solution. First, we convert the mass of Cl⁻ from milligrams to grams:

250.0 mg Cl⁻ = 0.250 g Cl⁻

Next, we need to find the moles of Cl⁻ using its molar mass (35.45 g/mol for Cl):

moles of Cl⁻ = 0.250 g / 35.45 g/mol = 0.00705 moles Cl⁻

Since one formula unit of AlCl₃ contains three chloride ions, we have:

moles of AlCl₃ = moles of Cl⁻ / 3 = 0.00705 / 3 = 0.00235 moles AlCl₃

Finally, the concentration (molarity) of the AlCl₃ solution is calculated by dividing the moles of AlCl₃ by the volume of the solution in liters:

molarity = 0.00235 moles / 0.150 L = 0.0157 M

Therefore, the correct answer is C) 1.57 x 10⁻² M.