Question

josh prepares a solution by mixing sodium nitrate and water. to calculate the molarity of the solution, josh should calculate the moles of which substance, and why?
○ sodium nitrate, because it is the solvent
○ sodium nitrate, because it is the solute
○ water, because it is the solvent
○ water, because it is the solute

Explanation:

1. Recall the definitions: In a solution, the solute is the substance being dissolved, and the solvent is the dissolving medium. Here, sodium nitrate is dissolved in water, so sodium nitrate is the solute and water is the solvent.
2. Recall the formula for molarity: Molarity ($M$) is defined as moles of solute per liter of solution ($M=\frac{\text{moles of solute}}{\text{liters of solution}}$). To calculate molarity, we need the moles of the solute. Since sodium nitrate is the solute, we calculate the moles of sodium nitrate. The other options are incorrect: sodium nitrate is not the solvent (so first option is wrong), water is the solvent (not solute, so third and fourth options are wrong as they misclassify water and also use the wrong substance for molarity calculation).

Answer:

B. sodium nitrate, because it is the solute