A solution is made by dissolving 10.9 g of calcium chloride, CaCl2,in enough water to make exactly 500 mL of solution. What is the concentration (molarity) of CaCl2 in mol/L?

Just remember the definition.

M = moles/L of solution.

moles = grams/molar mass

To find the concentration (molarity) of calcium chloride (CaCl2) in the solution, you need to determine the number of moles of CaCl2 dissolved in 500 mL of solution.

First, convert the given mass of calcium chloride (10.9 g) to moles. To do this, divide the given mass by the molar mass of CaCl2.

The molar mass of calcium (Ca) is approximately 40.08 g/mol, and the molar mass of chlorine (Cl) is approximately 35.45 g/mol. Since CaCl2 consists of one calcium atom and two chlorine atoms, the total molar mass of CaCl2 is:

Molar mass of CaCl2 = (1 × molar mass of Ca) + (2 × molar mass of Cl)
= (1 × 40.08 g/mol) + (2 × 35.45 g/mol)
= 40.08 g/mol + 70.9 g/mol
= 110.98 g/mol

Now, calculate the number of moles of CaCl2:

Number of moles = Mass of CaCl2 / Molar mass of CaCl2
= 10.9 g / 110.98 g/mol
≈ 0.0982 mol

Next, determine the volume of the solution in liters. The given volume is 500 mL, which needs to be converted to liters by dividing by 1000:

Volume of solution = 500 mL / 1000 mL/L
= 0.5 L

Now that you have the number of moles (0.0982 mol) and the volume (0.5 L), calculate the concentration (molarity) using the formula:

Molarity (M) = Number of moles / Volume of solution

Molarity = 0.0982 mol / 0.5 L
≈ 0.1964 mol/L

Therefore, the concentration (molarity) of CaCl2 in the solution is approximately 0.1964 mol/L.