Module 6

Task 1. Remember the following word:

solutе – раствор, растворенное вещество naked eye – невооруженный глаз concentrate – концентрировать, выпаривать homogeneous – однородный solid – твердое тело, твердый heterogeneous – разнородный sodium chloride – поваренная соль contaminate – загрязнять, отравлять

density – плотность volume – объем fraction – фракция, часть miscible – смешивающийся, растворимый complex – сложный liquid – жидкость gas – газ saturate – насыщать, пропитывать

Task 2. Consult the dictionary and read the international words

homogeneous,heterogeneous, colloids,suspensions,emulsions, phase,

concentration, physical, substance, nitrogen, oxygen, filter, salt,

physical, carbon dioxide, sodium chloride, electrolytes, basically, polymer, phase

Task 3. Translate the words with the same roots

Solve – dissolve – dissolving, solute – solution – solvent – solubility,

concentrate – concentration, stable – stability, filter – filtration, carbon – carbonated, plastic – plasticize – plasticizers, gas – gaseous, act – action – interaction, concentrate – concentration, create – creation – recreationally, saturate – saturated, contaminatе – contamination

Task 4. Read the text and translate it. Make up a plan that will help you to speak about solutions and their properties:

Solution

In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent (from the Latin solvō, "I loosen, untie, I solve"). The solvent does the dissolving. The solution

more or less takes on the characteristics of the solvent including its phase, and the solvent is commonly the major fraction of the mixture. The concentration of a solute in a solution is a measure of how much of that solute is dissolved in the solvent. A solution is a homogeneous mixture. A solution is a single phase system. The particles of solute in solution cannot be seen by naked eye. The solution does not allow beam of light to scatter (рассеиваться).

A solution is stable. The solute from the solution cannot be separated by filtration (or mechanically).

Homogeneous means that the components of the mixture form a single phase. The properties of the mixture (such as concentration, temperature, and density) can be uniformly distributed through the volume but only in absence of diffusion phenomena or after their completion. Usually, the substance present in the greatest amount is considered the solvent. Solvents can be gases, liquids or solids. One or more components present in the solution other than the solvent are called solutes. The solution has the same physical state as the solvent.

If the solvent is a gas, only gases are dissolved under a given set of conditions. An example of a gaseous solution is air (oxygen and other gases dissolved in nitrogen). Since interactions between molecules play almost no role, dilute gases form rather trivial solutions. In part of the literature, they are not even classified as solutions, but addressed as mixtures.

If the solvent is a liquid, then gases, liquids, and solids can be dissolved. Here are some examples:

Gas in liquid: oxygen in water, carbon dioxide in water – a less simple example, because the solution is accompanied by a chemical reaction (formation of ions). Note also that the visible bubbles in carbonated water are not the dissolved gas, but only an effervescence (бурное вспенивание, выделение пузырьков) (выделение пузырьков газа) of carbon dioxide that has come out of solution; the dissolved gas itself is not visible since it is dissolved on a molecular level.

Liquid in liquid: the mixing of two or more substances of the same chemistry but different concentrations to form a constant. (Homogenization of solutions); alcoholic beverages are basically solutions of ethanol in water.

Solid in liquid: sucrose (table sugar) in water, sodium chloride (table salt) or any other salt in water, which forms an electrolyte: When dissolving, salt dissociates into ions.

Counterexamples are provided by liquid mixtures that are not homogeneous: colloids, suspensions, emulsions are not considered solutions.

Body fluids are examples for complex liquid solutions, containing many solutes. Many of these are electrolytes, since they contain solute ions, such as potassium. Furthermore, they contain solute molecules like sugar and urea. Oxygen and carbon dioxide are also essential components of blood chemistry, where significant changes in their concentrations may be a sign of severe illness or injury.

If the solvent is a solid, then gases, liquids and solids can be dissolved.

Gas in solids: hydrogen dissolves rather well in metals, especially in palladium; this is studied as a means of hydrogen storage.

Liquid in solid: mercury in gold, forming an amalgam, hexane in paraffin wax

Solid in solid: steel, basically a solution of carbon atoms in a crystalline matrix of iron atoms. Alloys (сплав) like bronze and many others.

Polymers containing plasticizers.

When a liquid can completely dissolve in another liquid the two liquids are miscible. Two substances that can never mix to form a solution are called immiscible (несмешивающийся, несмешиваемый).

All solutions have a positive entropy (энтропия, неопределенность) of mixing. The interactions between different molecules or ions may be energetically favored or not. If interactions are unfavorable, then the free energy decreases with increasing solute concentration. At some point the energy loss outweighs the entropy gain, and no more solute particles can be dissolved; the solution is said to be saturated. However, the point at which a solution can become saturated can change significantly with different environmental factors, such as temperature, pressure, and contamination. For some solute-solvent combinations a supersaturated solution can be prepared by raising the solubility (for example by increasing the temperature) to dissolve more solute, and then lowering it (for example by cooling).

Task 5. Answer the following questions

1. What is a “solution”?

2. How is a substance dissolved in another substance called?

3. What does “concentration” mean?

4. What properties do solutions have?

5. What types of solvents were mentioned in the text?

6. What does the term “homogeneous” mean?

7. What types of solutions were mentioned in the text?

8. What solution can be called saturated?

9. What can significantly change the point at which a solution can become saturated?

Task 6. Match the words and their definitions

1. Homogeneous 2. Solution 3. Solute 4. Solubility 5. Saturated

a) means that no more solute particles can be dissolved b) is the ability of one compound to dissolve in another compound. c) is a substance dissolved in another substance, known as a solvent d) means that the components of the mixture form a single phase. e) is a homogeneous mixture

Task 7. Read the text and remember the information