Materials Used in Daily Life

We use many materials every day. Our kitchens and bathrooms are full of pots, pans, plates and buckets. We cook with salt, oil, spices, sugar, rice and pulses. We wash with soap and detergent. People build houses with iron and aluminium, and decorate them with marble and tiles. We wear jewelry of gold and silver.

All of these things take up space and have mass, so they are all matter. In this unit we look at what some of them are made of, what they are used for, and how to use them safely.

Many kinds of chemicals are used in daily life. A chemical is simply a substance: a particular kind of matter. Some chemicals come from nature, and some are made by people.

• Chuk is made by boiling down the juice of sour fruits, such as lemons, from plants.
• Baking soda is made from minerals.
• Ghee comes from the milk of cows and buffaloes.

Toothpaste, soap and the fertilizer spread in fields are all chemical substances too. Here we study two groups: chemicals used in food, and chemicals used for cleaning.

A. Chemicals used as food materials

Some cooks add a little baking soda to rice flour batter to make sel roti puff up. Baking soda is a chemical substance. So is salt. The sour taste of lemon, orange and amala comes from chemicals called acids in them. The sugar in tea is a chemical with a sweet taste.

Baking soda

Bread is soft and spongy. It is full of holes made by bubbles of gas. In cakes, biscuits and some breads, the gas comes from baking soda, which makes food light and helps it rise. (In most loaves of bread, it comes from yeast.)

The chemical name of baking soda is sodium bicarbonate (also called sodium hydrogen carbonate). It is made from minerals.

Uses of baking soda:

• to make bread, cakes, biscuits and sel roti soft and spongy
• in some fizzy drinks and fizzy powders
• as a medicine: it cancels out extra acid in the stomach (acidity)

Baking soda must be used in small amounts. Too much of it can cause bloating, vomiting and diarrhea.

Common salt

Edible salt (common salt) is a mineral. It comes from sea water, which is dried in the sun, and from rock salt dug out of the ground. Its chemical name is sodium chloride. It dissolves in water. Salt is one of our main sources of sodium, which our body needs.

Uses of salt:

• to give food its salty taste
• to keep fish, meat and pickles from going bad (to preserve them)
• in factories, to make soap, paper, rubber, glass and many other things
• for cleaning, and in medicines (such as the salt in oral rehydration solution)

Our body needs sodium chloride, but too much of it is harmful. Eating too much salt over many years can lead to high blood pressure, which can cause serious diseases of the heart and kidneys. Doctors advise adults to eat less than one teaspoon (5 g) of salt a day, and children less.

Sugar

Sugar tastes sweet. Its chemical name is sucrose. Most sugar is made from the juice of sugarcane, which grows in the Terai. Fruits such as bananas, mangoes, grapes and pineapples contain some sugar too.

Uses of sugar:

• to make food and drinks sweet
• to keep packed foods such as jam from going bad
• to make many drinks, because it dissolves easily in water

Ghee and oil

Ghee is a kind of fat made from the milk of cows and buffaloes. It is solid or liquid depending on how warm it is: solid in winter, and liquid in summer. Ghee is used to make sweets and tasty food. It is also rubbed on skin to keep it from drying.

Oil is a liquid fat, usually pressed out of the seeds of plants. The main oils used in Nepal are mustard oil, soybean oil, sunflower oil, flax seed (alas) oil, chiuri (butter tree) oil and olive (jaitun) oil.

Ghee and oil give us energy and keep our body warm.

B. Chemicals used as cleansers

Soap, shampoo and sanitizer are used at home for washing clothes, bathing and cleaning wounds. Today many kinds of cleaners are sold. Soap, detergent, phenol and stain remover are used to clean dirty dishes, windows, car glass and toilets.

Phenol

Phenol is a useful chemical. It is used as a disinfectant: a chemical that kills germs on floors, toilets and other things. It is used to clean houses, because it removes bad smells and keeps flies away. It dissolves easily in water.

Phenol is very poisonous. It burns the skin and can harm the eyes. Wear gloves when you use it, and keep it away from your eyes.

Antiseptic

An antiseptic is a chemical that kills germs, or stops them growing, on living skin. Antiseptics are used in surgery (operations), and to clean cuts and wounds. They dissolve in water. An antiseptic makes the skin free of germs.

Soap

Soap is a chemical used for cleaning. Most bars of soap are solid, and there are liquid soaps too. Different soaps are made for bathing and for washing clothes. When soap is rubbed in water it makes lather (foam).

Soap is made by boiling fats or oils with a strong chemical (lye). How does it clean? Water alone can’t wash away grease, because oil and water don’t mix. A soap particle is long, and its two ends are different: one end mixes with water, and the long tail mixes with oil and grease. The tails grab the grease, the other ends stay in the water, and when you rub, the grease is lifted off in tiny drops that the water rinses away (Figure 10.4).

Detergent

A detergent is a cleaning chemical in the form of a powder or a liquid, made mainly for washing clothes. It dissolves in water more easily than soap. It also works well in hard water, the water from some wells and taps in which soap makes a gray scum instead of lather. So clothes washed with detergent often come out cleaner than clothes washed with soap.

Stain remover

A stain remover is a chemical used to remove stains. Sometimes clothes, bed sheets, carpets and other things get stains that ordinary washing can’t remove, such as ink, paint, grease or nail polish. A stain remover dissolves the stain so that it can be washed away. Stain removers are sold as powders and as liquids.

1. Fill in the blanks with suitable words from the box

sodium · sodium chloride · sugarcane · baking soda · sugar

2. Choose the correct answer

3. Differentiate between

4. Answer the following questions

Hold a stick that is burning at one end, and the other end stays cool. But hold the end of a pair of iron tongs (chimta) whose other end is in the fire, and it burns your hand.

Electric wires are made of copper or aluminium. Most cooking pots are made of iron, copper, aluminium or steel, but shoes and slippers are made of rubber or plastic. Silver, copper, iron, aluminium and steel are hard, while rubber, plastic and wood are softer.

We sort the materials we use every day into metals and non-metals by their properties: Is it hard or soft? Does it let heat through? Does it let electricity through? Does it ring when it is struck?

A. Metals

We use both metals and non-metals every day. Metals are substances that are usually hard and shiny, can be beaten into sheets and drawn into wires, let heat and electricity pass through easily, and make a ringing sound when struck. Iron, copper, gold, silver and aluminium are common metals.

Physical properties of metals

The physical properties of a material are the things you can find out about it by looking, touching, hitting, heating or testing it, without changing it into a new substance.

1. Metals have luster

Metals reflect light, so they look bright and shiny. This shine on the surface of a metal is called metallic luster. Gold never loses its shine, and silver keeps it if it is cleaned now and then. That is why people make jewelry from them.

Many metals lose their shine in air, as a dull layer forms on them: iron rusts, and copper turns dark. Scratch or rub them, and the luster shows again underneath.

2. Metals are usually hard and solid

Iron and copper are hard metals. Not all metals are equally hard. Lithium, sodium and potassium are so soft that they can be cut with a knife, while hard metals can’t be cut easily.

At ordinary temperatures, almost all metals are solid. Mercury is the exception: it is a liquid metal.

3. Metals are sonorous

When a hard metal is struck, or two metals hit each other, the metal vibrates and makes a special ringing sound: “ting”. This property is called sonority, and metals are sonorous. That is why temple bells, school bells and singing bowls are made of metal.

4. Metals are malleable

Most metals can be hammered into thin sheets without breaking. This property is called malleability, and such metals are malleable. Because of it, metals are made into sheets of different shapes and sizes, for roofing sheets, pots and pans. Some metals are heated first to make them easier to shape, but gold, silver, copper and aluminium can be beaten into thin sheets even when cold.

5. Metals are ductile

Gold, silver, copper, iron and aluminium can be pulled (drawn) into long, thin wires. The property of being drawn into wires is called ductility, and such metals are ductile. Because of it, metals can be made into rods and wires of many sizes, such as the copper wires that carry electricity in our houses and the iron rods in buildings.

6. Metals are good conductors of heat

Heat passes easily through metals, so they are good conductors of heat. That is why cooking pots are made of metal, and why the hot handle of an iron pan burns you. Metals are also used in electric appliances for heating, such as electric kettles, irons and heaters.

7. Metals are good conductors of electricity

Electricity flows through metals such as zinc sheet, copper sheet, coins and iron nails. So metals are good conductors of electricity. Because electricity flows easily through metal, copper wire is used for the electric circuits in our houses. Many electric devices are made with copper and aluminium wires.

A mixture of a metal with other metals, or with carbon, is called an alloy. Alloys are often stronger or more useful than the pure metal. Steel is iron mixed with a little carbon, brass is copper and zinc, and bronze is copper and tin.

B. Non-metals

Many substances around us don’t have the properties of metals. These substances are called non-metals. Hydrogen, oxygen, nitrogen, sulphur and carbon are non-metals. Charcoal, coal and graphite are all forms of carbon, so they are non-metals too.

Non-metals don’t let heat and electricity pass easily (they are bad conductors). They are usually soft and dull, and they don’t ring when they are struck.

Physical properties of non-metals

1. Non-metals are found as solids (sulphur, carbon), as a liquid (bromine) and as gases (oxygen, nitrogen, hydrogen).
2. Non-metals are usually softer than metals. Diamond, a form of carbon, is the exception: it is the hardest natural substance.
3. Non-metals don’t make a ringing sound when struck.
4. Non-metals don’t have metallic luster. (Iodine and graphite are exceptions with some shine.)
5. Non-metals are not malleable: solid non-metals break or crumble when hammered. They are brittle.
6. Non-metals are not ductile: they can’t be drawn into wires.
7. Non-metals are bad conductors of heat and electricity. Graphite, another form of carbon, is the exception: it conducts electricity. (Graphite and diamond also carry heat well. Diamond carries it even better than copper, but it doesn’t conduct electricity.)

Differences between metals and non-metals

A. Cleaning chemicals

The chemicals used for cleaning, such as soap, shampoo, detergent and phenol, are made by people in factories. It is important to study how they affect our health and the environment before we use them, because some of them can be harmful. Using too much of them can pollute soil, water and air, and harm people, animals and plants.

For example, soap breaks down quickly in soil and water: tiny living things (bacteria) feed on it, until it is gone. It is biodegradable. Many detergents break down much more slowly, and some stay in the soil for a long time and spoil it. Detergent water poured on plants harms their growth. In streams and ponds, detergent harms fish and other water animals, and the phosphates in some washing powders feed water weeds and green scum (algae), which use up the oxygen that fish need.

B. Metals

Many things we need are made of metal. Walking along a road, we sometimes find thrown-away blades, nails and tin cans. Metal things don’t rot away in soil. Thrown away carelessly, they pollute the environment, and rusty blades and nails cut people and animals. To stop this, metal waste should be collected and reused or recycled.

Some metals are poisonous (toxic). Lead and mercury harm the brain, the kidneys and the nerves, most of all in children. Cobalt is needed by the body in tiny amounts, but larger amounts are harmful. When such metals get into water, they harm fish and other water animals, and they can reach us through the fish we eat. Such metals must be handled and thrown away with care: old batteries, broken thermometers and tube lights should never go into a river or a fire.

C. Minerals and fuels

Burning fossil fuels is a major cause of air pollution. Coal, diesel and petrol are widely used as fuels today. When they burn, they put smoke and carbon dioxide into the air. Using other sources of energy, such as electricity from rivers (hydropower) and the Sun, instead of such fuels helps to control air pollution.

Mining and processing minerals also harm the environment: they pollute water, air and soil. For example, cement is made by heating limestone in huge kilns. A cement factory pollutes the air around it with dust, and the limestone itself gives off carbon dioxide when it is heated.

1. Fill in the blanks with suitable words from the box

mineral · transfer · metal · iron

2. Choose the correct answer

3. Differentiate between

4. Answer the following questions