Solution Concentration

For chemical reactions that take place in solution the chemist needs to express the amount of material (solute) in a given amount of dissolving material (solvent). Generally, concentration is the ratio of the amount of solute to amount of solvent. There are several ways to express concentration. We will examine the most common ones used in chemistry.

Molarity

Molarity is define as the number of moles of solute per liter of solvent.

What is the Molarity of a solution prepared by dissolving 8.0 grams of NaOH in H₂O so that the final volume is 250 ml?

First convert grams to moles:

Then calculate the molarity

Mass Percent

Another way to express concentration is using Mass Percent.

Calculate the the mass percent of ethanol in a solution prepared by mixing 1.00 g of ethanol C₂H₆O with 100.0 g of H₂O.

Dilution

Often times solutions of a given concentration are prepared by diluting solutions of higher concentration. Here's an example of how to calculate how much a concentrated solution needs to be diluted to prepare a given concentration.

How many milliliters of 16 M HNO₃ must be used to prepare 1.0 liters of a 0.10 M HNO₃ solution?

So 6.2 ml of 16 M HNO₃ diluted to 1 liter will give 0.10 M HNO₃.