How many grams of KCl are needed to prepare 250 mL of a 2 M solution? (2023)

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Question: How many grams of KCl are needed to prepare 250 mL of a 2 M solution? (2023)

Options:

Correct Answer: 37.25 g

Solution:

Molar mass of KCl = 74.55 g/mol. Grams = moles × molar mass = 0.5 moles × 74.55 g/mol = 37.25 g.

How many grams of KCl are needed to prepare 250 mL of a 2 M solution? (2023)

How many grams of KCl are needed to prepare 250 mL of a 2 M solution? (2023)

Step 1: Understand that a 2 M (molar) solution means there are 2 moles of KCl in 1 liter (1000 mL) of solution.
Step 2: Since we need to prepare 250 mL, we first convert 250 mL to liters: 250 mL = 0.250 L.
Step 3: Calculate the number of moles needed for 250 mL using the formula: Moles = Molarity × Volume (in L). So, Moles = 2 M × 0.250 L = 0.5 moles.
Step 4: Find the molar mass of KCl, which is 74.55 g/mol.
Step 5: Calculate the grams of KCl needed using the formula: Grams = Moles × Molar Mass. So, Grams = 0.5 moles × 74.55 g/mol = 37.25 g.

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, typically expressed in grams per mole.
Dilution and Concentration Calculations – Calculating the amount of solute needed for a specific volume and concentration of solution.