2. Lead in. Work with the text.

1. Match the words with their definitions.

1. limit	a. the act or an instance of purifying or of being puri tied
2. clcctrolyte	b. used in or developed for use in industry
3. purification	e. the act or process of concentrating
4. industrial	d. a prescribed maximum or minimum amount, quan­tity, or number
5. suspension	e. to adjust or put in order
6, to settle out	f. a substance that when dissolved in a suitable solvent or when fused becomes an ionic conductor
7. solvent	g. a dissolved substance
8. solute	h. the amount of a substance that will dissolve in a given amount of another substancc
9. concentrauon	i. the state of a substance when its particles arc mixed with but undissolved in a fluid or solid
10. solubility	j a usually liquid substance capable of dissolving or dispersing one or more other substances

2. Translate into Ukrainian.

1. In the normal solution (e.g. sugar and water), the dissolving sub­stance (or solute) separates into molecules that become evenly dispersed throughout the solvent.

2. Acids, bases and salts separate into smaller particles than mole­cules when they are dissolved in water.

3. Therefore molecules of acids, bases and salts in the aqueous solu­tion dissociate into ions consisting of electrically charged atoms or groups of atoms.

4. The dissociation into ions takes place only at the time the solute is dissolved.

5. An ion is an atom or a group of atoms bearing an electric charge, or a number of such charges.

6. There arc two types of ions: the positive ions, cations, which move toward the negative electrode, cathode; and the negative ions, anions, winch move toward the positive electrode, anode.

7. Solutions of acids, bases and salts conduct an electric current and so they arc called electrolytes.

8. Solutions of sugars, alcohol and other substances do not conduct a current and therefore are non-electrolytes.

9. Since the solution of any electrolyte is electrically neutral, the total charges carried by the positive ions are equal to those carried by negative ions.

3. Read and translate the text. Solutions

A solution is a homogeneous mixture of two or more substances in relative amounts that can vary continuously up to the limit of solubili­ty (saturation), if any, of one in the other. In all solutions the dis­solved substance is called the solute, and the medium in which it is dissolved is the solvent.

Most solutions are liquids, but solutions also can be of gases or solids - for example, air (composed primarily of oxygen and nitrogen) or brass (composed chiefly of copper and zinc). In solutions compris­ing a solid dissolved in a liquid, the liquid is the solvent, and the solid is the solute; if both components are liquids, the one present in a smaller amount is usually considered the solute. If the saturation point is passed, excess solute separates out. Substances with ionic bonds (e.g. salts) and many with covalent bonds (e.g. acids, bases, alcohols) undergo dissociation into ions on dissolving and are called electro­lytes. Their solutions can conduct electricity and have other properties that differ from those of nonelectrolytes.

Solutions are involved in most chemical reactions, refining and purification, industrial processing, and biological processes. All sam­ples of a solution have the same properties (homogenous), but the components of a solution may be combined in different proportion of weight (variable composition), according to the concentration.

When we shake up a finely-divided solid with a liquid, the latter becomes dull, or cloudy. The solid particles are here simply suspended in the liquid but not dissolved, and will in the end settle out. Such mixtures are called suspensions.

When milk is allowed lo stand, the droplets of oily matter rise slowly to the top (as cream). They are lighter than the water in which they are not dissolved but dispersed, A mixture of two liquids of this type is called an emulsion.

The most useful and the commonest solvent is water, in which many inorganic substances dissolve easily. Some organic substances such as fats, paraffin, rubber, petroleum do not dissolve in water. But they dissolve in ether, chloroform or benzene.

The solubility of a substance (at the existing temperature) means the number of grams of the solute required to saturate a fixed volume or a fixed weight. The solubility of a substance depends very largely upon the temperature: the solubility of solids in liquids increases with the rise in temperature.

A dilute solution contains little dissolved matter. A concentrated solution contains a considerable amount of the dissolved substance and the solution can be made with very soluble solutes only.

The concentration of the solution is the amount of the substance which has been dissolved by a given quantity of the solvent. The par­tial removal of the solvent (by evaporation) is called concentrating. The total removal of the solvent is termed evaporating to dryness.