Ways+of+Expressing+Concentration

Concentration can be expressed qualitatively or quantitatively. Qualitative concentration is not an exact measurement, but is useful for describing general concentration. //**Dilute**// and **//concentrated//** are examples of qualitative concentration. A solution with a small concentration is said to be dilute, whereas one with a large concentration is said to be concentrated.

This guy's diluting a substance

Some ways of expressing concentration quantitatively are mass percentage, mole fraction, molarity, and molality. If a solution is 44% HCl by mass, then there's 44g HCl in 100g of HCl solution.

Another way to express concentration is //**parts per million (ppm)**//.

A solution that has a concentration of 1 ppm has one gram of solute for 1,000,000 g of solution. Parts per million is used for calculating the maximum allowable amount of something in a solution, for example, the maximum amount of arsenic in drinking water allowed is 0.010 ppm. **//Parts per billion (ppb)//** is also used when getting to really small concentrations.

Instead of using mass to calculate concentration, you can also use moles. The **//mole fraction//** (//X//) represents a ratio of the amount of a certain component per the total of all the components. The sum of the mole fractions of all components in a solution will equal 1. This fraction has no units because the numerator's and denominator's units cancel each other out. 

The mole fraction is very similar to //**molarity**//. Molarity is expressed as moles per liter. Remember the Molarity doorway.
 * //Molality//**, which is different from molarity, is the number of moles per kilogram of solvent. Molality and Molarity are very similar, but molality is based on mass, where molarity is based on volume. An interesting note: when water is the solvent in a very dilute solution, molarity and molality are about equal. 1 kg of water has a volume of 1 L, so the molarity and molality are the same.

__Sources__ http://www.chemistryland.com/CHM107Lab/Lab5/Soil/PourDiluteIntoTestTube.jpg http://www.cherrylanecollection.com/photos/9988.jpg Bursten, Brown, & LeMay. Chemistry: The Central Science, 9th Edition. [|http://mooni.fccj.org/~ethall/2046/ch13/molarity.gif] http://www.markrosengarten.com/Cartoons/5molarsolution.jpg