To find the molarity of a solution, such as aqueous potassium dichromate ($\text{K}_2\text{Cr}_2\text{O}_7$), you need to know the mass of the solute dissolved and the total volume of the solution. Molarity (M) is defined as the number of moles of solute per liter of solution. $$ \text{Molarity (M)} = \frac{\text{moles of solute}}{\text{volume of solution (L)}} $$ Here's how to calculate it: Step 1: Determine the moles of the solute. First, find the molar mass* of the solute. For potassium dichromate ($\text{K}_2\text{Cr}_2\text{O}_7$): Molar mass of K = $39.10 \text{ g/mol}$ Molar mass of Cr = $52.00 \text{ g/mol}$ Molar mass of O = $16.00 \text{ g/mol}$ Molar mass of $\text{K}_2\text{Cr}_2\text{O}_7 = (2 \times 39.10) + (2 \times 52.00) + (7 \times 16.00) = 78.20 + 104.00 + 112.00 = 294.20 \text{ g/mol}$ Next, measure the mass of the solute* (e.g., in grams) that was dissolved. Calculate the moles of solute using the formula: $$ \text{Moles of solute} = \frac{\text{mass of solute (g)}}{\text{molar mass of solute (g/mol)}} $$ For example, if you dissolved $14.71 \text{ g}$ of $\text{K}_2\text{Cr}_2\text{O}_7$: $$ \text{Moles of K}_2\text{Cr}_2\text{O}_7 = \frac{14.71 \text{ g}}{294.20 \text{ g/mol}} = 0.0500 \text{ mol} $$ Step 2: Determine the volume of the solution in liters. Measure the total volume of the solution* (not just the solvent) in milliliters (mL) or cubic centimeters ($\text{cm}^3$). Convert the volume to liters (L) by dividing by $1000$: $$ \text{Volume (L)} = \frac{\text{Volume (mL)}}{1000 \text{ mL/L}} $$ For example, if the solution was made up to a total volume of $250 \text{ mL}$: $$ \text{Volume (L)} = \frac{250 \text{ mL}}{1000 \text{ mL/L}} = 0.250 \text{ L} $$ Step 3: Calculate the molarity. Divide the moles of solute (from Step 1) by the volume of the solution in liters (from Step 2): $$ \text{Molarity (M)} = \frac{\text{moles of solute}}{\text{volume of solution (L)}} $$ Using the example values: $$ \text{Molarity} = \frac{0.0500 \text{ mol}}{0.250 \text{ L}} = 0.200 \text{ mol/L} $$ So, the molarity of the potassium dichromate solution is $\boxed{0.200 \text{ M}}$.