Normal Solutions

Normal solutions, titrated solutions, containing in 1 liter as many grams of a substance as there are units in the number expressing its chemical equivalent. The weight amount of substance corresponding to one equivalent is called the equivalent, or normal weight; hence the term N. r. The normal weight, in contrast to the molecular weight, is not constant for a given substance; it depends on the type of reaction, and where a substance can enter into reactions in different ways, it takes different values for N. r., for example chromic acid H₂CrO₄: 1) Acidimetric titration H₂CrO₄ + 2H⁺ + CrO₄^2- + 2H⁺ + 2OH^- → 2H₂O. Chromic acid is dibasic, therefore the equivalent weight equals half the molar weight [N = M/2]. 2) As an oxidizing agent 2H₂CrO₄ → Cr₂O₃ + 2H₂O + 3O (from two molecules of H₂CrO₄ - 3O, which is equivalent to 6H). Therefore one equivalent corresponds to one-third of the molar weight (N = M/3). Normal solutions are equivalent to each other, hence they enter into interaction with equal volumes. N. r. are designated 1N; N or 1.0N; 1/10N; n; 1.0 n. To obtain stronger or weaker solutions, titrated solutions are used that are multiples or fractions in relation to the concentration of N. r.; for example, 2-normal solutions are made, containing two equivalents in 1 liter. In practice, weaker solutions are more often used: containing 1/10 of the normal weight in 1 liter - decinormal solutions; they are denoted as ¹/₁₀ N or 1/10N or 0.1N, as well as 1/10n; n/10 or 0.1n solutions. In microanalysis, even more diluted solutions are used, containing 1/100 of the normal weight - centinormal solutions (1/100 N; 0.01 N; 0.01 n); sometimes solutions of other concentrations are also used. - Normal weights of the most common substances (in grams per 1 liter of N. r.): H₂SO₄ - 49.0378; HCl - 36.4648; NaOH - 40.0048; Na₂CO₃ - 52.997; H₂C₂O₄ + 2H₂O - 63.0234; Na₂C₂O₄ - 66.997; KMnO₄ - 31.6068; K₂Cr₂O₇ - 49.038; Na₂S₂O₃ + 5H₂O - 248.192; I₂ - 126.93; KIO₃ - 35.672; KIO₃ - HIO₃ - 32.588; AgNO₃ - 169.888; NH₄CNS - 76.1072; NaCl - 58.454.