Preparation of bases

1. Reactions of active metals (alkaline and alkaline earth metals) with water

2Na + 2H2O → 2NaOH + H2

Ca + 2H2O → Ca(OH)2 + H2

2. Interaction oxides of active metals with water

BaO + H2O → Ba(OH)2

3. Electrolysis water solutions of salts

2NaCl + 2H2O → 2NaOH + H2 + Cl2

Chemical properties of bases

Alkalis Insoluble bases

1. Action to indicators ––

litmus - blue

methylorange - yellow

phenolphthalein – crimson

2. Interaction with acid oxides

2KOH + CO2 → K2CO3 + H2O ––

KOH + CO2 → KHCO3

3. Interaction with acids (reaction of neutralization)

NaOH + HNO3 → NaNO3 + H2O Cu(OH)2 + 2HCl → CuCl2 + 2H2O

4. Reaction of exchange with salts

Ba(OH)2 + K2SO4 → 2KOH + BaSO4↓

3KOH + Fe(NO3)3 → Fe(OH)3↓ + 3KNO 3 ––

5. Thermal decomposition

–– tоС

Cu(OH)2 → CuO + H2O

43)

Syrak

.Guldberg and P.Waage (1867) clearly stated the Law of Mass Action (sometimes termed the Law of Chemical Equilibrium) in the form: the rate of any chemical reaction is proportional to the product of the masses of the reacting substances, with each mass raised to a power equal to the coefficient that occurs in the chemical equation. “Active mass” was interpreted as concentration and expressed in moles per liter. By applying the law to homogeneous systems, that is to systems in which al1 the reactants are present in one phase, for example in solution, we can arrive at a mathematical expression for the condition of equilibrium in a reversible reaction.

The laws of mass action have universal importance in chemistry. The law of mass action is a reaction that states that the values of the equilibrium – constant expression K_c are constant for a particular reaction at a given temperature, whatever equilibrium concentrations are substitute.

aA + bB ↔ cC + dD

Theme: Application of the law of mass action to the process of dissociation of water. pH scale.

Chemically pure water conducts an electric current very poorly and has an electrical conductivity of 0.055 µS∙ cm^{− 1}. But nevertheless it has a measurable electrical conductivity that is explained by the slight dissociation of water into hydrogen and hydroxide ions (According to the theories of Svante Arrhenius):

H₂O → H⁺ + OH^–

The electrical conductivity of pure water can be used to calculate the concentration of hydrogen and hydroxide ions in water. Let us write an expression for the dissociation constant of water:

We can rewrite this equation as follows:

[H⁺]∙ [OH^–] = [H₂O]∙ K

Replacing the product [H₂O]∙ K in the last equation with the new constant K_w, we have:

[H⁺]∙ [OH^–] = K_w

The latter K_w is called the ion product of water (or ionization constant, dissociation constant, self-ionization constant). The K_w value is depended of temperature. For pure water at 25°C K_w=10^-14, we have

[H⁺] = [OH^-] = 1·10^-7 mol/L.

Hence, for this temperature:

K_w = 10^-7 ∙ 10^-7 = 10^-14

Solutions in which the concentrations of the hydrogen ions and hydroxide ions are the same are called neutral solutions.