a) Calculate the molarity of a solution made by dissolving 12.5 grams of Na 2 CrO 4 in enough water to form exactly 750 mL of solution.

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Ch.4 - Reactions in Aqueous Solution

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Brown 14th Edition

Ch.4 - Reactions in Aqueous Solution

Problem 62a

Chapter 4, Problem 62a

a) Calculate the molarity of a solution made by dissolving 12.5 grams of Na₂CrO₄ in enough water to form exactly 750 mL of solution.

Verified step by step guidance

Step 1: Begin by determining the molar mass of Na2CrO4. To do this, add the atomic masses of all the atoms in the compound: 2 sodium (Na), 1 chromium (Cr), and 4 oxygen (O) atoms. Use the periodic table to find these values.

Step 2: Convert the mass of Na2CrO4 from grams to moles using the molar mass calculated in Step 1. Use the formula: \( \text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} \).

Step 3: Convert the volume of the solution from milliliters to liters, as molarity is expressed in moles per liter. Use the conversion: \( 1 \text{ L} = 1000 \text{ mL} \).

Step 4: Calculate the molarity of the solution using the formula: \( \text{Molarity (M)} = \frac{\text{moles of solute}}{\text{volume of solution in liters}} \).

Step 5: Review the calculation steps to ensure accuracy and consistency in units, and understand how each part contributes to finding the molarity.

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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 first determine the number of moles of the solute, which can be found by dividing the mass of the solute by its molar mass, and then divide that by the volume of the solution in liters.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all the atoms in a molecule. For Na2CrO4, the molar mass can be calculated by adding the molar masses of sodium (Na), chromium (Cr), and oxygen (O) in the correct proportions, which is essential for converting grams of the compound to moles.

Volume Conversion

Volume conversion is the process of converting a volume measurement from one unit to another, which is crucial in chemistry for accurate calculations. In this case, the volume of the solution is given in milliliters (mL) and must be converted to liters (L) for the molarity calculation, as molarity is defined in terms of liters of solution. The conversion factor is 1 L = 1000 mL.