# A water sample has .00505 grams of Arsenic in 12 Liters. what's the arsenic concetration in parts per million?

0.00505 g / 12,000 g = 4.2 x 10^-7 parts per 1
4.2 x 10^-7 x 10^6 = 4.2 x 10^-1 ppm = 0.42 ppm
ppm is define as mg / liter

= (0.00505 g * 1000 mg / grams) / 12 liters

= 0.421 ppm As
Quoted from the MSDS HyperGlossary:

Parts per million (PPM). Parts per million works like percent by mass, but is more convenient when there is only a small amount of solute present. PPM is defined as the mass of the component in solution divided by the total mass of the solution multiplied by 10^6 (one million):

ppm calculation is

Parts per Million = (mass of component/Mass of solution)x 10^6

A solution with a concentration of 1 ppm has 1 gram of substance for every million grams of solution. Because the density of water is 1 g per mL and we are adding such a tiny amount of solute, the density of a solution at such a low concentration is approximately 1 g per mL. Therefore, in general, one ppm implies one milligram of solute per liter of solution.

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0.00505 grams = 5.05 mg in 12 liters.

5.05/12= 0.42 parts per million of Arsenic.= 0.42 mg. per liter.

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