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Ch.4 - Reactions in Aqueous Solution
Chapter 4, Problem 54a

How many grams of solute would you use to prepare the following solutions? (a) 500.0 mL of 1.25 M NaOH

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Determine the molarity equation: Molarity (M) = \( \frac{\text{moles of solute}}{\text{liters of solution}} \)
Convert the volume of the solution from milliliters to liters: 500.0 mL = 0.5000 L
Use the molarity equation to find the moles of NaOH: \( \text{moles of NaOH} = \text{Molarity} \times \text{Volume in liters} \)
Calculate the molar mass of NaOH: Na (22.99 g/mol) + O (16.00 g/mol) + H (1.01 g/mol) = 39.99 g/mol
Convert moles of NaOH to grams using the molar mass: \( \text{grams of NaOH} = \text{moles of NaOH} \times \text{molar mass of NaOH} \)

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molarity (M)

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in moles per liter (mol/L). Understanding molarity is crucial for calculating how much solute is needed to achieve a desired concentration in a given volume of solution.
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Molarity Concept

Moles of Solute

A mole is a unit that quantifies the amount of substance. One mole contains approximately 6.022 x 10^23 entities (Avogadro's number). To find the number of moles needed for a solution, you multiply the molarity by the volume of the solution in liters, which is essential for determining how much solute to weigh out.
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Mole Fraction Formula

Mass of Solute

The mass of solute can be calculated using the formula: mass = moles × molar mass. The molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). This concept is vital for converting the calculated number of moles into grams, allowing for the accurate preparation of solutions.
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