How to Calculate Normality in Chemistry

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Measurements of concentration are an important part of chemistry, as they allow for an understanding of how much of a substance is present in a given amount of a solution. There are many different ways of calculating concentration, but most of them hinge on the number of moles (a measurement of a specific amount of any substance) of the dissolved substance (called the solute) per liter of the solvent (the liquid that is doing the dissolving). Normality is one measure of concentration that is sometimes used for salts, acids and bases, because it accurately describes the amount of each type of ion in a solution.

    Weigh the amount of solute (the thing to be dissolved) using a digital scale. Your weight should be measured in grams.

    Calculate the molar weight of the solute. This can be calculated by adding up the molar weight of each component of the solute. For example, one mole of the salt MgCl2 is made up of 1 mole of magnesium (with a molar weight of 24.3 grams per mole) and 2 moles of chlorine (with a molar weight of 35.5 grams per mole). As a result, the molar weight of MgCl2 is 95.3 grams per mole.

    Divide the amount of solute from Step 1 by the molar weight of the solute to get the number of moles of solute that you have. For example, if you had 95.3 grams of MgCl2 in Step 1 and then divided by the molar weight of MgCl2, you would find that you had 1 mole of MgCl2.

    Divide the number of moles of the solute by the volume that they are dissolved in. This will give you the normality of the solution. Volumes can usually be measured by using a piece of glassware called a graduated cylinder. For example, if you have 95.3 grams of MgCl2 (which is one mole of MgCl2) dissolved in 1 liter of water, then your normality would be 1N. N stands for "normal," which is the unit of normality.

    When calculating the normality of individual ions in a solution, multiply the normality that you calculated in Step 4 by the number of each type of ion present in your solute. For example, a 1N solution of MgCl2 would have magnesium ions present at 1N (because there is one molecule of magnesium in MgCl2) and would have chloride ions present at 2N (because each molecule of MgCl2 has 2 chloride ions).

    Things You'll Need

    • Scale
    • Graduated cylinder
    • Periodic table with molar weights
    • Calculator (optional)

About the Author

Adam Cloe has been published in various scientific journals, including the "Journal of Biochemistry." He is currently a pathology resident at the University of Chicago. Cloe holds a Bachelor of Arts in biochemistry from Boston University, a M.D. from the University of Chicago and a Ph.D. in pathology from the University of Chicago.

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