How to Calculate Standards for Analytical Chemistry

In chemistry experiments, you often will have to experimentally determine the quantity of a solute in a solution. For instance, you might need to determine the quantity of iron oxide in a solution, using thermogravimetric analysis (TGA). In order to do so, you should make standard solutions of the iron oxide, or substance in question, containing known quantities of the substance. You can use your standards to construct a calibration curve that graphs machine readouts vs. known concentrations of iron oxide. You can use this curve to estimate the concentrations in your experimental samples.

Instructions

    • 1

      Determine how concentrated your standards should be. If you expect your experimental solution to be around 0.3 M, then start your standards around 1 M. If you expect your experimental solution to be closer to 0.03 M in concentration, then start your standards around 0.2 M.

    • 2

      Create your most concentrated standard. To make a 1 M standard, calculate the molar mass of 1 mole of the substance that you are measuring. If the substance is NaCl, for instance, consulting a periodic table shows that the atomic weight of Na is 23 and the atomic weight of Cl is 35.5; thus, the molar mass of NaCl is 35.5+23=58.5 grams.

    • 3

      Use a balance to weigh out 58.5 grams of NaCl, then add 1 liter of distilled water to the mass to obtain a 1 M solution of NaCl.

    • 4

      Calculate your other standards by cutting the amount of NaCl in each subsequent standard by half. For instance, if your most concentrated standard is a 1 M solution, the next standard could be 0.5 M, then 0.25 M, then 0.125 M, and so forth. A 0.5 M solution will contain 29.25 grams of NaCl, a 0.25 M solution will contain 14.625 grams, and so forth.

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