Final answer:
The need to subtract the mass of sugar from a water solution in a lab depends on the experiment's goals. Generally, the mass of the solution is the sum of the mass of sugar and water. Subtracting occurs only in specific contexts, such as when the mass of the solvent alone is required.
Step-by-step explanation:
The question of whether you need to subtract the mass of sugar from a water solution in a lab depends on the experiment. In general, you do not subtract the mass of sugar from the solution because the mass of the solution is the sum of the mass of the solute (sugar) and mass of the solvent (water). This is expressed in the equation: mass of solution = mass of solute + mass of solvent. However, in specific experiments where only the mass of the solvent is of interest, you might subtract the mass of the solute to obtain it. Using an example, if a solution is prepared by dissolving 25.0 g of sugar into 100.0 g of water, the mass of the solution would be the sum of both, which is 125.0 g. Analysis of mass percent or concentration would then be based on these masses.
In experiments involving solubility, you reach a point where no more solute (sugar) can be dissolved in the solvent (water), known as the solution's solubility. In these cases, any additional undissolved solute would not count towards the total mass of the solution unless you were measuring the excess.