Final answer:
The question asks about the amount of an 85% solution of lactic acid with a specific gravity, but provides incomplete information for a direct answer. Dilution concepts and density calculations related to such problems are discussed, using the provided dilution examples of acetic acid and methanol solutions.
Step-by-step explanation:
The original question appears to be incomplete as it requests the amount of an 85% w/w solution of lactic acid with a specific gravity of 1.21 but does not specify what amount of the final solution or dilution is needed. However, understanding how dilution affects concentration can be explained using an example similar to the one provided about dilution of acetic acid and methanol solutions.
Dilution refers to the process of reducing the concentration of a solute in a solution, typically by adding more solvent. When diluting a solution, the concentration of the solution decreases while the total amount of solute remains constant. This relationship is often represented by the formula C1V1 = C2V2, where C1 and C2 are the concentrations before and after dilution, and V1 and V2 are the volumes before and after dilution.
In the case of diluting a stock solution of 5.00 M concentration from 0.85 L to 1.80 L, the new concentration can be calculated using this formula. The result, 0.629 M, makes sense as it is indeed less than half the original concentration (5 M), providing a good check for computational accuracy. Such calculations can also apply when, for example, a 25.0 mL of a 2.04-M solution of CH3OH is diluted to 500.0 mL.
Finally, density is an important consideration when dealing with solutions. The density of a substance is the mass per unit volume and for liquids, it is often expressed in g/mL. For instance, the density of a sample can be calculated by dividing its mass by its volume, as shown in an exercise where a 2.130 mL sample of acetic acid with a mass of 2.234 g has its density calculated in g/mL.