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Ch.5 - Introduction to Solutions and Aqueous Solutions
Chapter 5, Problem 21c

Calculate the molarity of each solution. c. 132.4 mg NaCl in 255.4 mL of solution

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Convert the mass of NaCl from milligrams to grams by dividing by 1000.
Calculate the number of moles of NaCl using the formula: \( \text{moles} = \frac{\text{mass (g)}}{\text{molar mass of NaCl (g/mol)}} \). The molar mass of NaCl is approximately 58.44 g/mol.
Convert the volume of the solution from milliliters to liters by dividing by 1000.
Use the formula for molarity: \( M = \frac{\text{moles of solute}}{\text{liters of solution}} \) to find the molarity of the NaCl solution.
Ensure all units are consistent and check calculations for accuracy.

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Key Concepts

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

Molarity

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in units of moles per liter (mol/L). To calculate molarity, one must know the amount of solute in grams, convert it to moles using the molar mass, and then divide by the volume of the solution in liters.
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Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). For sodium chloride (NaCl), the molar mass is calculated by adding the atomic masses of sodium (Na) and chlorine (Cl). This value is essential for converting grams of solute into moles, which is a necessary step in determining molarity.
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Volume Conversion

Volume conversion is the process of changing the volume measurement from one unit to another, such as from milliliters (mL) to liters (L). Since molarity is defined in terms of liters, it is crucial to convert the volume of the solution to liters by dividing the volume in milliliters by 1000. This ensures that the molarity calculation is accurate.
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