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Name: Lakshita Status: student Grade: 9-12 Country: China Date: Spring 2013

Question:
How can you figure out the relative concentration of solution?

Replies:
Hi Lakshita,

Thanks for the question. The easiest way to find the concentration of a solution is through titration, if possible. Alternatively, one could take a known volume of the solution and evaporate the known volume. Then the sample is weighed. One can then calculate the concentration of solute in the solution.

I hope this helps. Thanks Jeff Grell


Lakshita,

I am not certain what you mean by "relative" concentration. Solution concentrations are always descriptions of how much of one substance there is relative to another. Whether it be molarity: the moles of solute relative to the liters of solution, molality: the moles of solute relative to the kilograms of solvent, mole fraction: the moles of one substance relative to the sum of the moles of all the substances in the solution, we're always talking about how much of one substance there is relative to other substances in the solution. This means that to know the concentration of a solution, we need to know the amounts (whether it be in grams, moles, volume, or some other measure) of the substances in the solution.

If by "relative concentration" you mean using one solution to find out the concentration of another - then this is a particular experiment process (such as titration or gravimetry) where we use a known reaction ratio between two substances, use a known amount of one substance, and by determining how much of that substance reacted, we can determine (using the known reaction ratio) how much of the other substance there is.

Greg (Roberto Gregorius) Canisius College


Hi Lakshita,

There are many methods. One convenient way is to do it by mole/liter. Calculate gms/(gms/mole) = moles, then work up the dilution to the working volume of the solution and calculate what the concentration would be in one liter, moles/liter.

Then you are able to look at the concentration of all reactants or analytes relative to each other as conditions change.

Some disciplines have, for practical reasons, determined that one method of making comparisons is better than others. An example is the medical application of partial pressures of gases. In the medical sciences, pO2 and pCO2 are preferred over molar concentrations.

Peter E. Hughes, Ph.D. Milford, NH


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