High School

2. Calculate the molarity of each solution.

(a) 33.2 g of KCl in 0.895 L of solution

(b) 61.3 g of C₂H₂O in 3.4 L of solution

(c) 38.2 mg of KI in 112 mL of solution

Answer :

The molarity of the KCl solution is 0.497 M. The molarity of the C₂H₂O solution is 0.321 M. The molarity of the KI solution is 0.0021 M.

(a)

Mass of KCl = 33.2 g

The volume of solution = 0.895 L

the number of moles present in KCl is:

Molar mass of KCl = 39.10 g/mol + 35.45 g/mol

KCl molar mass = 74.55 g/mol

Number of moles of KCl = mass of KCl / molar mass of KCl

Number of moles of KCl = 33.2 g / 74.55 g/mol = 0.445 mol

The molarity of KCl is:

Molarity = number of moles of solute / total volume of solution

Molarity = 0.445 mol / 0.895 L

Molarity = 0.497 M

Therefore, we can infer that the molarity of the KCl solution is 0.497 M.

(b)

Mass of C₂H₂O = 61.3 g

The volume of the solution = 3.4 L

Molar mass of C₂H₂O solution = 2(12.01 g/mol) + 2(1.01 g/mol) + 16.00 g/mol

Molar mass of C₂H₂O solution = 56.03 g/mol

Total Number of moles of C₂H₂O = mass of C₂H₂O / molar mass of C₂H₂O

Total Number of moles of C₂H₂O = 61.3 g / 56.03 g/mol = 1.094 mol

The molarity of the solution is:

Molarity = number of moles of solute/volume of solution in liters

Molarity = 1.094 mol / 3.4 L = 0.321 M

The molarity of the C₂H₂O solution is 0.321 M.

(c)

Mass of KI = 38.2 mg

The volume of the solution = 112 mL

Molar mass of KI = 39.10 g/mol + 126.90 g/mol = 166.00 g/mol

Total number of moles of KI = mass of KI / molar mass of KI

Total number of moles of KI = 38.2 mg / 166.00 g/mol = 0.00230 mol

Here we need to convert the milliliters to liters.

Volume of solution = 112 mL ÷ 100 = 0.112 L

Now, we can calculate the molarity:

Molarity = number of moles of solute/volume of solution in liters

Molarity = 0.000230 mol / 0.112 L = 0.0021 M

The molarity of the KI solution is 0.0021 M.

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