Video Transcript
Which of the following is the formula for calculating the concentration of a solution? (A) Concentration equals total volume of solution divided by number of moles of solute. (B) Concentration equals number of moles of solute minus total volume of solution. (C) Concentration equals number of moles of solute multiplied by total volume of solution. (D) Concentration equals number of moles of solute divided by total volume of solution. (E) Concentration equals total volume of solution plus number of moles of solute.
To begin, we probably remember that molarity is defined as the number of moles of solute per liter of solution. Molarity is also called molar concentration. Let’s think about this a little more. Suppose we have a glass of water with some salt dissolved in it. In the salt water solution, the salt is the solute, while the water is the solvent. If we tasted the water, we’d note its salty flavor. If we add more salt to the water and taste the water again, it tastes saltier. It tastes saltier because we increased the concentration of salt in the solution.
What happens if instead of adding more salt we add more water? Then, the solution doesn’t taste as salty. This is because when we added water, we increased the volume of the solution but did not change the amount of salt dissolved. The result is that the concentration of salt in the solution decreases.
From this example, we can see that the concentration or saltiness is related to the amount of stuff dissolved, whether that’s a salt or any other solute, divided by the volume of the solution. Finally, we should consider the amount of stuff dissolved more accurately as the number of moles of solute dissolved. This means that the concentration is equal to the number of moles of solute divided by the total volume of solution. Therefore, answer choice (D) is correct. Concentration equals number of moles of solute divided by total volume of solution.
