What you are given, 0.3181 N, is the normality of HCl. Normality in chemistry means various amounts, but the most common use, especially in acid-base chemistry, is that the normality is the moles of H+ or OH- ions present in the acid or base per liter. Since HCl has only one H+ ion, its molarity is also 0.3181 M.
To convert molarity to molality, we have to take note that molarity, denoted by the capital letter M, is the number of moles per liter solvent, or mol/L Molality, meanwhile, denoted by the lowercase letter m, is the number of moles per kilogram solvent, or mol/kg. This means that we must have the density of the solvent, as much as possible in kg/L.
Therefore, we can write a formula of coverting molarity to molality as follows:
HCl is usually prepared in an aqueous solution, so we can safely assume that the solvent is water, which has the density of 1 kg/L. Therefore using the formula,
For more molality problems, check out:
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