Question

(Help would be greatly appreciated, chemistry is not my strong suit) How many moles of NaCl are present in a solution with a molarity of 8.59M and 125mL of a solution?
1. 1.07g
2. 62.7mol
3. 1.07mol
4. 62.7g

Answer 1

Molarity is a unit of concentration defined as the number of moles of solute (the substance being dissolved) per volume of solution (the solvent in which all the solute is dissolved). Mathematically, molarity is expressed as

$M = \frac{\text{ mol solute}}{\text{ L solution}}$.

In this question, we are given the molarity and the volume of a solution of NaCl. We can use this information to calculate the number of moles of NaCl present in the solution. Rearranging the equation to solve for moles of solute, we multiply the molarity by the volume of the solution (the units for volume must be in liters, so 125 mL is expressed as the equivalent 0.125 L):

$(8.59 \text{ M})(0.125 \text{ L}) = 1.07 \text{ moles of NaCl}.$

The question asks for the number of moles of NaCl in this solution, so number 3 would be correct.