For english-speaking students of veterinary medicine faculty. Part 1 / Е. Ю. Микрюкова, А. В. Жарехина, А. М. Галиева – казань: кгавм, 2017. – 66 С.

 

 

Учебно-методическое пособие по неорганической  химии предназначено для иностранных студентов первого курса факультета ветеринарной медицины. По каждой теме приводится необходимый теоретический материал, а также примеры решения типовых задач, задания для подготовки к промежуточному и итоговому контролю, образцы тестов и указания к выполнению лабораторных работ. В конце приведены экзаменационные вопросы и необходимый справочный материал

 

 

ã МикрюковаЕ.Ю., Жарехина А.В., Галиева А.М.

ã федеральное государственное бюджетное образовательное учреждение высшего     образования «Казанская государственная академия ветеринарной медицины Н.Э. Баумана», 2017

Class 1.

Topic: Concentration units.

 

The relative content of a substance is known as it’s concentration, that on other hand means the content of solute (in g or Mol) in unit of mass or volume of solution or solvent.

We use approximate and exact ways of concentration expressions. To characterize the concentration approximately we usually use following definitions: dilute, concentrated, unsaturated, saturated, supersaturated.

The exact ways of concentration expression are the following:

1.Mass fraction or percentage of solute ω(x) is the ratio of solute mass(m(x)) and the solution mass (m(solution)), this value is dimensionless and is expressed in fractions from unit or in percent (%) and likewise in thousandth fractions (‰) or in millionth fractions (mln^-1). For instance ω(x) = 0,005 = 0,5% =5‰ = 5000 mln^-1.

In medical literature mass fraction is often expressed in gram-percent (g%) (equally percentage), milligram-percent (mg% or 10^-3 g%) and mikrogram-percent (mkg % or 10^-6 g%). Therefore ω(x)= 0,005 = 0,5 g% = 500 mg% = 500000 mkg%.

For example 5% solution is 5-percent solution or solution with mass fraction of solute equal to 5% or 0,05.

2. Mole fraction χ(x) – is the relation of number of moles of solute ν(x) to the total number of moles of all components of solution Σν(x_i).

This is dimensionless value, expressed in fractions of unit or in percent.

3.Volume fraction: φ(x) –is the relation of volume of the solution component (liquid) V(x) to the total volume of solution (liquids mixter) V(solution). It is likewise expressed in fractions of unit or in percent.

4.Molar concentration or molarity C(x) is the relation of number of moles of solute ν(x) to the volume of solution V(solution), whose dimension is mol/l. For instance, 0,1M solution means decimolar solution or solution with molarity of solute equal to 0,1 mol/l.

5. Molar concentration of equivalent (normality) C(1/z x) is the relation of number of moles of equivalent of solute ν(1/z x) to the volume of solution; its dimension is mol/l.

The term “equivalent” is connected with some definite reaction in which this substance takes part. Equivalent (1/z x) is the conventional or real particle of X which in given acid-base reaction is equivalent to one proton or to one electron in given oxidation-reduction reaction. Equivalent of one-basic acids or one-acidic bases is always real particle that is the molecule X. As for polyprotic acids and multi acidic bases their equivalent can be equal to the real molecule X or some it’s fraction- 1/z x. Number, that point to fraction of real particle, which is equivalent to one proton in acid-base reactions or to one electron in ox-red reactions is named factor of equivalence (f_eq(x) or 1/z x). Examples of determinations of equivalents are given below.

If two substances take part in chemical reaction such as X₁ and X₂,according to the “law of equivalents” number of moles of equivalent of the first consumed substance ν(1/z x₁) is equal to number of moles of equivalent of the second: ν(1/z x₂) or:

                                ν(1/z x₁) = ν(1/z x₂).

If acid-base reaction proceeds completely we mast take into account that Z is the basicity of the acid or acidity of the base and as for salts is the product of number of metal atoms, forming this salt, and metal’s valency.

One mole of equivalents of X contains Avogadro’s number of particles (6,02∙10²³ of X equivalents). Molar mass of equivalent 1/z∙x is determined as product of equivalent’s factor and molar mass of the substance:

                             M(1/z∙x) = 1/z∙M(x)

Solutions with definite normality C(1/z∙x) are used for absolutely concrete reactions.

For instance: 0,01N solution whose normality is equal to 0,01 Mol/l.

6. Molality (molal concentration) of the solution b(X) is determined as relation of number of moles of solute ν(x) to the mass of solvent m(solvent); dimension - Mol/kg. May be assumed the following symbolizes: for normality: N(X) instead of C(1/z∙x); for molality C_m(X) instead of b(X).

Titre (or mass concentration) t(X) is the relation of solute mass to the volume of solution; dimension – g/ml.

Formulas used to calculate all concentration mentioned above are given in the table 3 placed in appendix.

According to the “law of equivalents” if solutions of two substances with volume of V(sol-n X₁) and V(sol-n X₂) and normalities of C(1/z∙x₁) and C(1/z∙x₂) and titres of t(X₁) and t(X₂) correspondingly react, we can write the equations

V(s-n X₁) C(1/z∙X₁)      m(X₁) V(s-n X₁)∙t(X₁)   M(1/z∙X₁)

———— = ————; ——— = —————— = ————

V(s-n X₂) C(1/z∙X₂)      m(X₂) V(s-n X₂)∙t(X₂)    M(1/z∙X₂)

Tasks with their solutions