excellent conductors of electrical current - gold, copper, iron, aluminum, alloys.Along with them, there is a large group of substances, non-metals, melts and aqueous solutions also have the property of conductivity.This strong bases, acids, some salt, collectively referred to "electrolytes".What is the ionic conductivity?Let us find out what have substance-electrolytes to this common phenomenon.
which particles carry charges?
around the world is full of different conductors and insulators.On these properties, bodies and substances known since antiquity.Greek mathematician Thales had experience with amber (in Greek - "electron").Rubbing it on silk, scientists have observed the phenomenon of gravity hair, wool fibers.Later it became known that amber is an insulator.This substance no particles that could carry an electric charge.Good conductors - metals.They include atoms are present, positive ions and free, infinitely small negative particles - electrons.They provide transfer charges when current is passed.Strong electrolytes in dry form do not contain free particles.But by dissolving and melting the crystal lattice is destroyed and the polarization of a covalent bond.
Water, electrolytes and non-electrolytes.What's dissolution?
Giving or join electrons, atoms of metallic and non-metallic elements are converted into ions.Between them in the crystal lattice there are quite a strong link.Dissolving or melting of ionic compounds, such as sodium chloride, resulting in its destruction.In polar molecules no related or free ions, they come in contact with water.In 30-ies of the XIX century, Michael Faraday discovered that solutions of some substances conduct electricity.The scientist introduced into science such important concepts:
- ions (charged particles);
- electrolytes (conductors of the second kind);
- cathode;
- anode.
There are connections - strong electrolytes, lattices that completely destroyed with the release of ions.
there are insoluble materials and those that are stored in the molecular form, e.g., sugar, formaldehyde.Such compounds are called non-electrolytes.For them, characterized by the formation of charged particles.Weak electrolytes (coal and acetic acid, ammonium hydroxide and other substances) are low in ions.
theory of electrolytic dissociation
In his works, the Swedish scientist S. Arrhenius (1859-1927) was based on the findings of Faraday.In the future, the situation clarified his theory of Russian researchers I. heels and B. Kistyakovsky.They found that the dissolution and melting of ions do not constitute all the substances, and electrolytes only.What is the dissociation of S. Arrhenius?This is the destruction of molecules, which leads to the appearance of the charged particles in solutions and melts.The main theoretical position S. Arrhenius:
- bases, acids and salts in the solution is in a dissociated state.
- reversibly dissociate into ions strong electrolytes.
- little weak form of ions.
indicator of the degree of dissociation of matter (often expressed as a percentage) is the ratio of the number of molecules broken into ions, and the total number of particles in solution.Electrolytes are strong, if the value of this parameter over 30%, the weak - less than 3%.
Properties electrolytes
theoretical conclusions S. Arrhenius supplemented later studies of physical and chemical processes in solutions and melts, conducted by Russian scientists.An explanation of the properties of acids and bases.The former include the compounds in solutions of cations which can only detect the metal ions are anions OH⁻ particles.Acid molecules break down into negative ions acid residue of hydrogen and protons (H +).The movement of the ions in solution and melt - chaotic.Consider the results of the experiment, which would require to collect the chain include the carbon electrodes and the common light bulb.Verify the conductivity of solutions of different substances: sodium chloride, sugar and acetic acid (the first two - electrolytes).What is the electric circuit?This current source and conductors interconnected.With the closure of the circuit will burn brighter than the light in a solution of salt.The movement of ions becomes ordering.Anions are directed to the positive electrode and cations - to negative.
In this process, acetic acid is involved in a small amount of charged particles.Sugar is not an electrolyte does not conduct.Between the electrodes in this solution would be the insulation layer, the light will not illuminate.
chemical interaction between electrolyte
When pumping solutions can observe the behavior of electrolytes.What is ionic equations such reactions?Consider the example of chemical reaction between barium chloride and sodium nitrate:
2NaNO3 + BaCl2 + = 2NaCl + Ba (NO3) 2.
Formula electrolytes can be written in ionic form:
2Na + + 2NO3- + Ba2 + + 2Cl- = 2Na + + 2Cl- + Ba2 + + 2NO3-.
Taken reaction substances - strong electrolytes.In this case, the composition of the ions is not changed.The chemical interaction between the electrolyte solutions in the three possible cases: 1. If
one product is an insoluble substance.
Molecular equation: Na2SO4 + BaCl2 = BaSO4 + 2NaCl.
write the composition of electrolytes in the form of ions:
2Na + + SO42- + Ba2 + + 2Cl- = BaSO4 (white precipitate) + 2Na + 2Cl-.
2. One of the compounds formed - gas.
3. Among the products of the reaction is a weak electrolyte.
Water - one of the most weak electrolytes
Chemically pure water (distilled) does not conduct an electric current.But within it there is a small number of charged particles.This protons H + and OH- anions.Dissociation is subject to a negligible number of water molecules.There magnitude - ionic product of water, which is constant at 25 ° C.It allows you to know the concentration of H + and OH-.Predominate hydrogen ions in acid solution, the hydroxide anion more in alkalis.In neutral - it matches the number of H + and OH-.Wednesday solution also characterizes the pH value (pH).The higher it is, the more hydroxide ions present.Wednesday is neutral in the pH range close to 6-7.In the presence of H + and OH- change color substance-indicators: litmus, phenolphthalein, methyl orange and others.
properties of solutions and melts of electrolytes are widely used in industry, technology, agriculture and medicine.Scientific substantiation laid by a number of prominent scientists, to explain the behavior of the particles that make up salt, acids and bases.These solutions occur multiple ion exchange reaction.They are used in many industrial processes, electrochemistry, electroplating.Processes in living beings also occur between the ions in solution.Many non-metals and metals, toxic as atoms and molecules that are essential in the form of charged particles (sodium, potassium, magnesium, chlorine, phosphorus and others).
