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How Do I Go From NG/Ml to Molarity?

Scientists and engineers use different units to measure different quantities and concentrations. A forester might use board feet per acre to measure a timber lot's lumber content; an environmental researcher will use parts per million (ppm) or parts per billion (ppb) to characterize the concentration of mercury in river water and a chemist might specify molarity (M) when he's describing the concentration of a substance in solution. Converting a given solution value in nanograms per milliliter (ng/ml) to molarity, or moles per liter, is straightforward.

Things You'll Need

Pencil
Paper
Scientific calculator

Instructions

- 1
  Write the name of the solute in the solution you are analyzing. The solute of a solution is the substance that is dissolved in the solution. For example, you are analyzing a solution of sodium hydroxide (NaOH) in water. You write, "NaOH."
- 2
  Consult a textbook or online chemical compound database and learn the molecular weight (MW) in grams per mole (g/mol) of the solute in your solution. For example, you access PubChem Compound and learn the molecular weight of NaOH is 39.997110 grams per mole.
- 3
  Write the nanograms per milliliter (ng/ml) value of the solution you are analyzing. For example, write "17,000,000 ng/ml."
- 4
  Divide the number you have written by 1 x 10^9 using a scientific calculator to convert your value to grams per milliliter (g/ml). For example, 17,000,000/1 x 10^9 = 0.017.
- 5
  Divide your answer by the molecular weight of the substance, or solute, in the solution you are analyzing to convert your value to moles per milliliter. For example, 0.017/39.997110 = 4.25 x 10^(-4).
- 6
  Multiply your answer by 1,000 to convert your answer into moles per liter, or molarity. For example, 4.25 x 10^(-4) x 1000 = 0.425. A sodium hydroxide solution of 17,000,000 nanograms per milliliter (ng/ml) has a molarity of 0.425 M.

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