A solution is prepared by dissolving 20.2 mL of methanol (CH₃OH) in 100.0 mL of water at 25 °C. The final volume of the solution is 118 mL. The densities of methanol and water at this temperature are 0.782 g/mL and 1.00 g/mL, respectively. For this solution, calculate the concentration in each unit. c. percent by mass

Key Concepts

Concentration Units

Concentration can be expressed in various units, including molarity, percent by mass, and volume/volume percent. Percent by mass is calculated by taking the mass of the solute and dividing it by the total mass of the solution, then multiplying by 100. Understanding these units is essential for accurately describing the composition of a solution.

Density and Mass Calculation

Density is defined as mass per unit volume and is crucial for converting volumes of liquids into masses. For methanol and water, their respective densities allow us to calculate the mass of each component in the solution. This mass is necessary for determining the percent by mass of the solute in the final solution.

Final Volume of Solution

The final volume of a solution is the total volume after mixing the solute and solvent. In this case, the final volume is given as 118 mL, which is important for calculating the total mass of the solution. This total mass, combined with the mass of the solute, is used to find the percent by mass concentration.