Products of Chemical Changes

Various combinations of different elements produce all the forms of matter common to the earth: water, sugar, salt, and hundreds of thousands of others. These are chemical compounds which are produced by a chemical combination of two or more atoms.

One of the most important and the most know of all substances is water. However, water is not an element, as it may be divided into two entirely different substances. Water is, therefore, an example of a compound. Table salt is a common material, and it may also be divided into other substances, showing that it is a compound. Water is produced by combining hydrogen and oxygen, in the proportion of two atoms of hydrogen and one atom of oxygen. Salt is a compound of the elements sodium and chlorine, one atom of sodium and one of chlorine.

In chemical compounds the atoms are grouped into molecules. A molecule is, then, the smallest individual unit of a compound, and it will always consist of two or more atoms.

When elements go into chemical combinations, the properties will entirely change. For example, sodium is chemically a very active material, and chlorine is an active gas. When the atoms of these two elements combine, they form a mineral substance. As another illustration, hydrogen and oxygen are both gases, that combine chemically and from water. The composition of a compound may be shown by means of two methods, known as synthesis and analysis. Synthesis it the process of combining the elements forming the compound; analysis is the breaking down of the compounds into elements.

They very common substance water may be broken down into elements and these may be combined back again forming water. The determination of the masses making up water shows that the mass of water produced is the same as the sum of the masses of the two combining gases, while in the analysis of water the combined mass of the hydrogen and oxygen formed will be the same at the mass of water in the reaction.

 

Statements:

1. Various combinations of different elements produce all the forms of matter common to the earth: water, sugar, salt. 2. One of the most important and the most know of all substances is oxygen. 3. Water is produced by combining nitrogen and oxygen. 4.In chemical compounds the atoms are grouped into molecules. 5. When elements go into chemical combinations, their properties will not entirely change. 6. Synthesis is the breaking down of the compounds into elements. 7. Analysis is the process of combining the elements forming the compound. 8. Hydrogen and oxygen are both gases that combine chemically and form water.

 

Ключи к лабораторной работе 3:

Задание 1. 1. Время заседания перенесли. С тех пор многое изменилось. 2. Телефон – самое быстрое средство связи. Нет никакой возможности добраться отсюда до аэропорта в течение часа. 3. Когда это происходило? Это не повторится. Это растение встречается повсюду в Европе. 4. Они выпускают детские книги. Новые элементы были получены учеными в ядерных реакторах. Животные дают нам мясо и молочные продукты, а так же сырье и материалы для одежды и обуви. 5. Все цены подвергаются изменению. Темаегоисследованиябылаоченьинтересной.

Задание 2. Transformation, to be made of, to return, entirely, to allow, to obtain, to take place, for example.

Задание 3. Like, new, unchanged, different, liquid, naturally, a lot of (many), slowly.

Задание 4. Transformations are of two kinds, known as physical and chemical changes. 2. Thousands of physical and chemical changes take place in nature. 3. Physical transformations do not change the composition of the substances.4. Thus, in all these states, steam, water and ice are all the sane substance made up of the simpler substances, hydrogen and oxygen. 5. Thus,iron when is affected by moist air is slowly transformed into iron rust entirely different in its properties from the original iron.

Задание 5. 1- 8,9; 11- 5,6,7 III – 10,11,12;IV- 13,14,15; V- 1,2,3,4

Задание 6. 1-15; 2-14;3-13;4-12;5 -11; 6- 10; 7-9; 8-8; 9-7; 10-6;11-5;12-4;13-3;14-2; 15-1.

Задание 7. 1-5;2-4;3-3;4-2;5-1.

Задание 8. 1- it’sright; 2- it’s wrong; 3- it’s wrong; 4- it’s wrong 5- it’s right 6- it’s right; 7- it’s wrong; 8- it’s right.

Задание9. 1. Thousands of physical and chemical changes take place in nature. 2.In a laboratory it is possible to cause many other changes artificially which do not occur naturally. 3. Physical changes are those which affect the state or condition of matter without changing its composition. 4. Chemical changes are those matter without change of composition does take place. 5. The state but not the composition is affected by the process of heating or cooling. 6. Substance can be changed from one state into another. 7. Iron when it is affected by moist air is slowly transformed into iron rust entirely different in its properties from original iron. 8. Transformations are of two kinds know as physical and chemical changes. 9. In all three states, steam, water and ice are all the same substance made up of the simpler substances, hydrogen and oxygen.

Задание 10. 1 – true, 2- false, 3- false, 4- true, 5- false, 6- false, 7- false, 8- true.

 

 

Unit 4

Chemical Elements

The fact that a limited number of chemical elements compose all the mate­rials 6people find on earth shows the importance of each of them. Some of the elements are very common on the earth, others are rare. Many of the elements are never seen in pure form by most chemists, so rare are they. In fact, some seventy-five of the elements make up less than one per cent of the earth. How­-ever, the future may discover important uses for some of these little known and rare elements.

Elements are characterized by some properties distinguishing them from other substances. The main of these properties are their colour, hardness, odour, taste, density, solubility in water or other liquids, ability to conduct electricity and others. The ability to burn in air and the manner in which an element enters into chemical reactions with other substances are also properties that help to dis­tinguish one element from another. For example, oxygen is a colourless, odour­less, tasteless gas with a density at standard conditions of pressure and tempera­ture of about one seven-hundredth that of water. It is soluble in water, and it be­comes liquid at about 180° below zero on the centigrade thermometer.

Similarly, these properties determine whether a substance is necessary or useful industrially. Copper is of great value, being a good conductor of electric­ity. Carbon and hydrogen are also useful because they combine readily with oxygen, i.e. burn, and in so doing liberate great quantities of heat. Tungsten is valuable because of the several important properties it possesses. It is a hard metal which does not melt when it is heated to high temperatures producing white light. It does not rust and is not affected by cold acids. Thus it is very use­ful and is now considered one of the very important metals of industry.

The particles all the different atoms consist of are neutrons, protons (posi­tively charged particles) and electrons (negatively charged particles); therefore, the only way in which the chemical elements differ from each other in their composition is in the number and arrangement of these particles in their atoms. Similarly, many of the properties of the elements, both physical and chemical, are determined by the number and arrangement of these particles.