Final answer:
To make a 75% solution by mass, weigh 2250 g of solute for a total solution mass of 3000 g, then add water to reach the desired mass. Adjust the temperature to increase solubility if necessary. Use the mass of solution = mass of solute + mass of solvent formula for calculations.
Step-by-step explanation:
To create a 75% solution by mass, Guther needs to understand the process of calculating the mass of solute and solvent to use. The formula to use here is mass of solution = mass of solute + mass of solvent. If the objective is to make 3000 g of solution, Guther would weigh 2250 g (75% of 3000 g) of the solute and then add 750 g (3000 g - 2250 g) of the solvent to reach the desired percentage since the prepared solution always has the combined mass of the solute and the solvent.
It's important to note that solutions have different solubilities at different temperatures; thus, heating the solution could also increase solubility, allowing more solute to be dissolved before it settles out. This can be seen when making a solution of sodium chloride, where you would need to subtract the mass of NaCl from the total mass of the solution to determine how much water to add. Similarly, the concept of volume percent is relevant if both the solute and solvent are liquids. For instance, a solution with 40 mL ethanol added to 20 mL of water would be calculated as (40 mL/(40 mL + 20 mL)) x 100% to give the volume percent.