We use various substances in day to day life. We have previously learnt in some detail about a few of them, their uses and constituents and the method of their preparation.
The names of some substances in everyday use are given below. Classify them into groups like acids, bases, metals, non- -metals and salts.
Substances :Table salt, soap, toothpaste, baking soda, water, curds, milk, alum, iron, sulphur, washing powder.
Important salts in daily life
The ionic compounds which do not contain H+ and OH- ions and contain only one kind of cation and anion are called simple salts. For example, Na2 SO4 , K3 PO4 , CaCl2 .
Inorganic substances occur naturally in the form of salts rather than acids or bases. About 80 million tons of salts are added every year to seawater. Therefore, the sea is said to be a rich source of salts. In fact, the sea is a rich source of several salts of various elements such as chlorine, sodium, magnesium, potassium, calcium, bromine., However, we also use other salts apart from these in day to day life. Let us learn more about them.
Sodium chloride (Table salt- NaCl)
Table salt, or common salt, which gives a salty taste to food, is the most used of all salts. Its chemical name is sodium chloride. Sodium chloride is formed by a neutralization reaction between sodium hydroxide and hydrochloric acid. We have already seen that this is a neutral salt and that the pH value of its aqueous solution is 7.
Sodium bicarbonate (Baking soda – NaHCO3 )
Your mother brings cake on your birthday or makes it at home. She also makes crisp bhaji. Have you ever asked your mother what makes the cake porous or the bhaji crisp? Mother adds baking soda in the batter. Baking soda is a white noncrystalline powder. Its chemical name is sodium hydrogen carbonate or sodium bicarbonate and its molecular formula is NaHCO3
Bleaching powder (Calcium oxychloride CaOCl2 )
Tap water has a typical strong odour in the rainy season. Have you experienced it? Water in a swimming pool also has the same odour. It is the odour of the chlorine gas used to destroy the microbes in the water. Chlorine gas is a strong oxidizing agent and therefore, it has a strong disinfecting as well as bleaching action. Chlorine is inconvenient to handle because of its gaseous state. Instead, the solid bleaching powder which has the same effect is more convenient to use. Bleaching powder undergoes slow decomposition due to the carbon dioxide in air and chlorine gas is released. Bleaching powder gets its property because of this release of chlorine gas.
CaOCl2 + CO2 ® CaCO3 + Cl2 ®
Bleaching powder is obtained by the reaction of chlorine gas with slaked lime. Ca(OH)2 + Cl2 ® CaOCl2 + H 2 O
Washing soda Na2 CO3 .H2 O
Procedure : Take a sample of water from a well or a bore-well, in a beaker, add some soap to it and stir. Then take another sample, add one spoonful of washing soda and stir; then add some soap and stir again. Observe the changes that take place. Which changes did occur? Why do they occur? The hard water from a well or a bore-well becomes soft on adding washing soda and we come to know this from the lather formed on it. The hardness of water is due to the presence of chlorides and sulphates of calcium and magnesium in it. Na2 CO3 is added to it to soften such water and make it suitable for use. The reaction with Na2 CO3 causes the formation of insoluble carbonate salts of magnesium and calcium
MgCl2 (aq)+ Na2 CO3 (s) ® MgCO3 (s) + 2 NaCl(s
Sodium carbonate is a water soluble salt of sodium. Crystalline sodium carbonate,on keeping, loses its water of crystallization readily and a white powder is obtained. This powder is called washing soda.
Some crystalline salts
You have learnt about water of crystallization in the previous chapter. We use various salts which contain water of crystallization.
Some substances in our daily use which contain water of crystallization
- Alum (Potash alum – K2 SO4 .Al 2 (SO4 )3 .24H 2 O )
- Borax (Na 2 B4 O7 .10H 2 O)
- Epsom salt (Magnesium sulphate MgSO4 .7H 2 O)
- Barium chloride (BaCl 2 .2H 2 O)
- Sodium sulphate (Glauber’s salt Na 2 SO4 .10 H 2 O)
Collect more information on the properties and uses of the substances listed above. You have learnt that alum is used in the process of water purification. Because of property of coagulation, the solid impurities in water come together, become heavy and settle to the bottom. As a result, the water above becomes clear. Blue vitriol is used in the blood test for diagnosing anaemia. In the Bordeaux mixture which is used as a fungicide on fruits like grapes, musk melon, slaked lime it is used with blue vitriol.
When oil or animal fat is boiled with an aqueous solution of sodium or potassium hydroxide, sodium or potassium salts of carboxylic acids (fatty acids) are formed. These salts are called soap. When soap is mixed with hard water calcium and magnesium salts of fatty acids are formed. These being water insoluble they form a precipitate and that is why lather is not formed
Elements with a high atomic number such as uranium, thorium, radium have a property of spontaneously emitting invisible, highly penetrating and high energy radiation. This property is called radioactivity. A substance having this property is called a radioactive substance. The nucleus of radioactive elements is unstable. Radiation occurs from an unstable nucleus. Radioactive substances are relevant to our day to day life. However, before going further, let us learn something more about these substances. Three types of radiation are given out by radioactive substances. These are alpha, beta and gamma rays
Nature of radioactive radiation
In 1889 Rutherford discovered that the radiations emitted by radium were of two types. They are called alpha and beta radiation. Willard discovered the third type namely gamma radiation. When these rays are allowed to pass through two oppositely charged plates they get separated. This method was introduced by Rutherford in 1902. Rutherford and Willard studied the radiation emitted by radioactive substances. For this purpose, the rays were allowed to pass through an electrical field and a photographic plate was held in their path. It was found that the radiation was divided into three types. One type of radiation deviated slightly towards the negatively charged plate, while the second type of radiation deviated substantially towards the positively charged plate. However, the third type of radiation did not deviate at all in the electrical field. The rays which deviated slightly toward negatively charged plate are called alpha rays, those which deviate substantially towards the positively charged plate are called beta rays and those which do not deviate at all are called gamma rays.
Uses of radioactive isotopes : It is a misconception that radioactive elements are used only for making an atom bomb. Radioactive isotopes are used in various fields such as scientific research, agriculture, industry, medicine, etc. Radioactive substances are used in two ways.
- By using the radiation alone.
- By using the radioactive element itself.
Some chemical substances in day to day life.
The food that we eat, objects like clothes, utensils, watches, medicines and other objects are made from various kinds of matter. These affect our health directly or indirectly. Let us learn about some such substances.
Food colours and essences
Food colours are mixed in most soft drinks and foodstuffs available in the market. These food colours are in the form of powders, gels and pastes. Food colours are used in domestic as well as commercial products. Certain colours and essences are added to ice cream, ice candies, sauce, fruit juices, cold drinks, pickles, jams and jelly. Food colors are often found to be added to packaged meat (chicken, mutton), chilli powder, turmeric, sweets and other similar substances so as to give them a good colour.
The coloured substance which on applying to an article, imparts that colour to the article, is called a dye. Generally, a dye is soluble in water and insoluble in oil. Often a mordant has to be used to fix the colour after dying a cloth. Plants are the main source of colour for preparing a natural dye. Roots, leaves, flowers, bark, fruits, seeds, fungus and pistil are used for making dyes. In Kashmir a very good dye is made from saffron, which is used to dye fibres from which saris, shawls and dresses are made. These are very costly. Many people are engaged in this occupation as their means of earning a livelihood.The use of henna leaves to colour hair is safe for health.
William Henry Perkin invented an artificial dye in 1856. Artificial dyes are classified into many types on the basis of chemical properties and solubility. Petroleum products and minerals are used in these dyes.
We regularly use artificial colours on Rang Panchami, decorating the housd by painting. The red color use on Rang Panchami is very dangerous. It contains a high proportion of mercury in it. This poses risks like blindness, skin cancer, asthma, itching of the skin, permanent blocking of sweat pores etc. Therefore, it is necessary that artificial colours are used cautiously.
Body odour is caused by the bacterial decomposition of the sweat. A deodorant is used to prevent this odour. Everybody likes a fragrant deodorant to remain fresh the whole day. School children use deo on a large scale. This large scale use of deo in adolescent is a result of the advertisements shown on television. Deodorants contain parabens (methyl, ethyl, propyl, benzyl and butyl) and also alcohol in large proportions. Aluminium compounds and silica are also used.
- Ordinary deo – It contains a smaller proportion of aluminium. It decreases the odour of the sweat.
- Antiperspirant deo – This decreases the extent of sweating. It contains about 15% of aluminium chlorohydrate. It clogs the sweat pores on the skin.
- Clinical deo – Some people sweat heavily and it has harmful effects on the skin. Clinical deo is meant for such people. It contain 20 to 25% aluminium. It is used during the night.
- Aluminium – Zirconium compounds are the most harmful chemicals in the deodorant. Disorders like headache, asthma, respiratory disorders, heart disease are likely to occur without our knowledge.
- There is a possibility of various skin disorders and also skin cancer due to the aluminium chlorohydrates
Teflon is used for coating cooking utensils and industrial equipment to avoid sticking. It is the polymer of tetrafluoroethylene. Roy J. Plunkett discovered it in 1938. Its chemical name is polytetrafluoroethene (C2 F4 )n
Powder coating : Powder coating is a method of applying a layer harder than paint on the surface of an iron object to prevent rusting. In this method, a polymer resin, a pigment and some other ingredients are melt mixed, cooled and ground into a uniform powder. This powder is sprayed on the polished metal surface by electrostatic spray deposition (ESD). In this method, the particles of the powder are given an electrostatic charge due to which a uniform layer of the powder sticks to the metal surface. Then the object is heated in the oven along with the coating. A chemical reaction occurs in the layer, resulting in the formation of long cross-linked polymeric chains. This powder coating is highly durable, hard and attractive. Powder coating can be done on plastic and medium density fibre (MDF) board in day to day use as well.
Anodizing : A protective layer is formed naturally on the surface of aluminium metal by reaction with oxygen in air. In the anodizing process, this layer can be made of the desired thickness. Anodizing is done by electrolysis. Dilute acid is taken in the electrolytic cell and the aluminium article is dipped in it as the anode. When an electric current is passed hydrogen gas is released at the cathode and oxygen gas at the anode. A reaction with oxygen occurs and a layer of hydrated aluminium oxide is formed on the anode, i.e. the iron article..This layer can be made attractive by adding colour in the cell during electrolysis. We use anodized cooking utensils like griddles and cookers. Why?
Ceramic : Ceramic is a heat resistant substance formed by kneading an inorganic substance in water and then shaping it and hardening it by heating. Pots made by a potter, Mangalore roofing tiles, construction bricks, pottery, terracotta articles are some examples of common ceramic articles that we see around.
Porcelain : This is a hard, translucent and white coloured ceramic. It is made by using the white clay called kaolin, found in China. Glass, granite and the mineral feldspar is mixed with kaolin and kneaded with water. The resulting mixture is shaped and fired in a kiln at a temperature of 1200 to 1450 0 C. On firing again after glazing, beautiful articles of porcelain are obtained. Which porcelain vessels are used in the laboratory? Bone china – Bone china is made by adding some ash of animal bones in the mixture of china clay, feldspar and fine silica while making porcelain. This ceramic is harder than porcelain. Advanced ceramics : Oxides like Alumina (Al2 O3 ), Zirconia (ZrO2 ) Silica (SiO2 ) and some other compounds like silicon carbide (SiC), boron carbide (B4 C) are used instead of clay for making advanced ceramic. This ceramic requires a temperature of 1600 to 1800 0 C and an oxygen free atmosphere for firing. This process is called sintering.