How many grams of KCl are needed to prepare 250 mL of a 2 M solution? (Molar mas

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Question: How many grams of KCl are needed to prepare 250 mL of a 2 M solution? (Molar mass of KCl = 74.5 g/mol) (2023)

Options:

Correct Answer: 37.25 g

Solution:

Grams = moles × molar mass = (2 moles/L × 0.25 L) × 74.5 g/mol = 37.25 g.

How many grams of KCl are needed to prepare 250 mL of a 2 M solution? (Molar mass of KCl = 74.5 g/mol) (2023)

How many grams of KCl are needed to prepare 250 mL of a 2 M solution? (Molar mass of KCl = 74.5 g/mol) (2023)

Step 1: Understand that Molarity (M) is defined as moles of solute per liter of solution.
Step 2: Identify the desired molarity of the solution, which is 2 M (2 moles per liter).
Step 3: Convert the volume of the solution from milliliters to liters. Since 250 mL is equal to 0.25 L, we have 0.25 L.
Step 4: Calculate the number of moles needed using the formula: moles = Molarity × Volume. So, moles = 2 moles/L × 0.25 L = 0.5 moles.
Step 5: Use the molar mass of KCl, which is 74.5 g/mol, to find the mass in grams. Use the formula: grams = moles × molar mass.
Step 6: Substitute the values into the formula: grams = 0.5 moles × 74.5 g/mol = 37.25 g.
Step 7: Conclude that you need 37.25 grams of KCl to prepare the solution.

Molarity – Molarity (M) is a measure of concentration defined as moles of solute per liter of solution.
Molar Mass – Molar mass is the mass of one mole of a substance, expressed in grams per mole.
Volume Conversion – Understanding how to convert milliliters to liters is essential for calculating moles from molarity.