My Science School

WATER

Water is a tasteless, odorless liquid. Although it appears to be colourless, in fact it is very pale blue. Each molecule of water is made up of two hydrogen atoms and one oxygen atom, giving it the chemical formula H2O. Water is Earth’s most common compound, found everywhere, from the oceans that cover 71 per cent of the planet to each cell of every living organism.

• Unlike most compounds, water can exist in all three states of matter, solid, liquid, and gas, within Earth’s normal range of temperatures.
• At sea level, water is liquid between 0 and 100°C (32-212°F), but below 0°C (32°F), it solidifies into ice, and above 100°C (212°F), it becomes gaseous water vapour.
• Unlike most other substances, water is denser when it is liquid than when it is solid - that is why ice floats on the top of water instead of sinking.
• When water freezes into ice, it expands by nine per cent of its volume with a force that can burst pipes and split rock.
• Earth is the only place in the Solar System where conditions allow water to exist in liquid form at the surface. Some liquid water exists under the surface of the moons of Jupiter and Saturn.
• Water is essential for life, so astronomers look for it when searching for life on other planets.
• The body of an average adult man contains more than 40 litres (70 pints) of water.
• You need about 2 litres (4 pints) of water every day to keep healthy.
• About 30 per cent of the world’s population do not have clean, safe running water at home.
• Water is not a resource that can be used up like oil. Water evaporates into the air, forms clouds, and falls back to Earth as rain. In areas of Earth that receive little rainfall, water can be a scarce resource.

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MATERIALS

Almost everything around us is made from some sort of material. Each has different properties, such as strength or flexibility, which makes it useful for making particular products. Some materials, such as wool or stone, grow or occur naturally. Synthetic materials are manufactured. Composite materials combine the properties of two or more materials to achieve the best possible product.

1. SILK: This natural fibre is made from the cocoon of the silkworm. Each cocoon may produce 3 km (2 miles) of silk. Silk can be woven into an extremely fine fabric, and is prized for its texture and its shiny appearance.
2. CONCRETE: Concrete is made by mixing sand, gravel, cement, and water. It is a liquid when freshly made, so it can be poured into a mould, where it sets to form an extremely hard and durable material.
3. KEVLAR: A light, flexible, synthetic material, Kevlar is used for protective clothing, such as bulletproof vests. Kevlar molecules are arranged in long chains with strong bonds between them, which makes Kevlar five times stronger than steel.
4. WOOL: This natural material comes from the fleece of sheep. The structure of its fibres means wool has a tendency to shrink, so it is often mixed with synthetic fibres to make easy-care fabrics.
5. CARBON COMPOSITES: These materials are strong and light and can be turned into complex shapes, such as sports equipment. They are made from the carbon byproducts of coal, oil, and natural gas.
6. METAL: When heated, metals can be shaped into anything from a paperclip to an aircraft. They are also good conductors of heat and suitable for carrying electricity.
7. PLASTIC: This group of synthetic materials is made from petrochemicals (derived from crude oil). They are strong, light, cheap to make, and can be shaped into flexible sheets, films, or fibres.
8. GLASS: This transparent ceramic is made by fusing sand, limestone, and soda at high temperatures, or by recycling old glass. Molten glass can be shaped in many ways, such as into windows, lenses, and threads for optical fibres.
9. LYCRA: Synthetic fabrics are designed to have better properties than natural materials, such as cotton. Lycra is a stretchy fabric that keeps its original shape, making it perfect for sports clothes.
10. RUBBER Natural rubber is an elastic material made from latex, a milky fluid from the rubber tree. Synthetic rubber is made from petrochemicals. Rubber is used in tyres and for waterproofing fabrics.
11. NYLON: Developed in 1938, nylon was the first synthetic fabric. It can be produced in extremely fine threads, is cheap to manufacture, and was first used as a replacement for silk in stockings and parachutes.
12. CERAMIC: Ceramic materials are made by heating different types of clay to a high temperature. China, bricks, tiles, cement, and glass are all ceramics. These materials are hard, brittle, and resistant to heat.
13. WOOD: Wood is a strong material compared to its weight, and is a good building material. It is also used for furniture and art objects because of its attractive texture. It is referred to as hardwood or softwood, depending on the type of tree it comes from.
14. COTTON: Cotton is a natural material produced from the long, flexible fibres in the fluffy seedpods of the cotton plant. The fabric is soft, comfortable to wear, and there is no static build-up as there is with some synthetic fabrics.
15. STONE: Stone is a natural material quarried from the earth. It is hard and heavy and can withstand great pressure. Stone may be cut using diamond saws or extremely high-pressure jet of water.

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ACIDS AND BASES

An acid is a substance that produces positively charged particles of hydrogen, called hydrogen ions, when dissolved in water. The more hydrogen ions an acid contains, the stronger the acid is. A base is the chemical opposite of an acid. Bases produce negatively charged particles in water, called hydroxide ions. The more hydroxide ions a base contains, the stronger it is. Bases that dissolve in water are called alkalis.

• INDICATOR PAPER When a strip of indicator paper is dipped into a liquid, the paper changes colour. The colour can be compared to a pH scale to find out the acidity of the solution. pH stands for “potential of hydrogen”, and measures how many hydrogen ions the solution contains.
• CITRIC ACID The sharp taste in citrus fruit such as lemons and grapefruit is due to the citric acid they contain. Citric acid is often artificially added to manufactured foods and drinks to give a tangy sensation that tastes refreshing. Vinegar is made when bacteria convert the ethanol in alcohol into acetic acid.  
• VINEGAR The sour taste of vinegar comes from the acetic acid it contains. Every step on the pH scale is 10 times less acidic than the previous step, so acetic acid with a pH of 4 is 1,000 times less acidic than hydrochloric acid.
• HYDROCHLORIC ACID The lower the pH value, the stronger the acid. Hydrochloric acid, created when hydrogen chloride gas dissolves in water, has a pH of about 1. It is highly corrosive, capable of eating through metals.
• CHEMICAL HAZARD Strong acids and bases have to be stored in containers that will not be corroded by the chemical within. These containers are labeled with chemical hazard symbols that show the potential dangers.
• STINGER When a bee stings, it injects a mild acid into a person’s flesh, which causes a stinging sensation. Washing the sting with alkaline soap may relieve the pain by neutralizing the acid.
• LIQUID SOAP Soap is a weak base. It is made by combining a weak acid with a strong base, making it only mildly alkaline with a pH of about 8. An indicator paper dipped into liquid soap turns blue.
• LIMESTONE Calcium carbonate, or limestone, is a type of rock formed from the remains of Dead Sea creatures over millions of years. It is an important base, which is quarried and crushed to make fertilizers, paints, ceramics, and cement.
• WATER Pure water is neither acid nor alkali, but neutral, with a pH of 7. Rainwater is slightly acidic, with a pH of 5 to 6, while seawater is slightly alkaline, with a pH of between 8 and 9.
• CLEANING FLUID The strongest bases have a pH of 14 or more. Alkaline solutions with a high pH are used as cleaning materials as they dissolve fats. Cleaning fluids such as bleach and caustic soda have a pH of around 10.
• HYDRANGEAS The hydrangea shrub produces different coloured flowers depending on the acidity of the soil. On acid soils, it produces blue flowers, on alkaline soils, it produces pink or purple flowers, and on neutral soils, it has creamy white blooms.

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CHEMICAL REACTIONS

The atoms within a molecule are held together with links called chemical bonds. In a chemical reaction, the bonds between a molecule’s atoms break, and the atoms bond in a different way to form new molecules. In some reactions, elements combine to create a compound. In others, compounds break down into elements or simpler compounds. All the atoms from the original substance exist in the changed substance, but in different places.

1. REACTION When vinegar (acetic acid) and chalk (calcium carbonate) are mixed, a chemical reaction takes place. The acidic vinegar breaks down the chalk to release carbon and oxygen as bubbles of carbon dioxide. The starting materials in a chemical reaction are called reactants. The materials that exist after are called products.
2. DISPLACEMENT In a displacement reaction, the metal that forms part of a compound is removed and replaced by another metal. When a coil of copper is dipped into a clear solution of silver nitrate, the copper displaces the silver from the solution to form a blue solution of copper nitrate and needles of solid metal silver.
3. BURNING When the wick of a candle burns, it is reacting with oxygen in the air to produce ash and smoke. The burning also produces energy in the form of heat and light. In all reactions, energy is used up when bonds between atoms break, and energy is released as new bonds are made.
4. REACTION RATES The rate of a chemical reaction is affected by factors such as temperature, pressure, light, surface area, and concentration. It is possible to change the rate of a reaction by varying one of these factors. For example, increasing the concentration of dye in a solution will dye the material more quickly.
5. REVERSIBLE A few reactions are reversible. The molecules created by the reaction can be reformed into the original materials. The initial reaction is called the forward reaction and the reverse is the backward reaction. Dinitrogen tetraoxide breaks down into nitrogen dioxide when heated, but reverts when cooled.
6. APPLYING HEAT When a mixture of yellow powder sulfur and silver-grey iron filings is heated to a high temperature, a chemical reaction takes place and iron sulfide is formed. Without heat, the substances would not react with each other. Heat speeds up most reactions, and cold slows reactions down.
7. EXOTHERMIC Thermite is a mixture of aluminium and iron oxide. When it is ignited at a high temperature there is an explosion, as the chemical reaction produces a sudden release of energy in the form of light, heat, and noise. Reactions that produce heat are known as exothermic reactions.
8. OXIDATION Some chemical reactions happen around us naturally. One of the commonest reactions is oxidation - when substances gain oxygen. Oxidation is happening when metals rust, when wood burns, and when we breathe. In all these reactions, substances are reacting with oxygen from the air.
9. SOLUTIONS A solution is a mixture in which the molecules are mixed so evenly and completely that it seems like a single substance. However, in a solution, a chemical reaction has not taken place. Neither the solute (the substance being dissolved) nor the solvent (the substance that it is dissolved in) have changed.
10. CATALYST A catalyst is a molecule that helps bring about and speed up a chemical reaction, but does not change itself during the reaction. Natural catalysts are called enzymes. Bread dough rises because enzymes in yeast cause a reaction that produces bubbles of carbon dioxide when it is mixed with water and sugars.

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STATES OF MATTER

Everything you can smell, touch, or taste is made from matter, including living things such as yourself, and non-living things such as the book. Matter is made up of atoms and anything that is not made of matter is energy. Heat, light, and sound are forms of energy. You cannot smell, touch, or taste energy, and it is not made from atoms. All matter on Earth exists in one of three states: solid, liquid, or gas.

1. SOLID A solid, such as ice sculpture, has a fixed volume and a shape that is not easy to change. Strong links hold atoms together and do not allow them to move around, as they can in a liquid and in a gas. The atoms in most solids are arranged in regular patterns that form three-dimensional shapes, such as cubes and prisms, called crystals.
2. GAS A gas does not have a fixed shape or a fixed volume. It expands to fill all the space around it. Atoms in a gas can move freely in every direction. They whizz around far too fast to ever stick together.
3. LIQUID A liquid does not have a fixed shape, but does have a fixed volume. Its atoms can move past each other, allowing the liquid to flow so that it takes up the shape of its container. Atoms in a liquid are linked together more strongly than in a gas, but not as strongly as in a solid.
4. STATE TO STATE Matter changes from one state to another when it is heated or cooled. Heating melts solids into liquids and boils liquids to form gases. Cooling condenses gases to form liquids and freezes liquids into solids. As matter changes from one state to another, the atoms within it remain the same but become arranged differently.
5. CHANGING SHAPE Solids do not always have a fixed shape. Some solids, such as ice or glass, are brittle and will break if you hammer or crush them. Other solids, such as rubber or metals, are malleable and can be hammered, stretched, or squashed into different shapes without breaking.

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ELEMENTS 

Everything in the world is made from elements - pure substances that cannot be broken down into anything simpler. Elements can be grouped according to the properties they have in common, such as their appearance, how they conduct electricity, and how they react with other substances. There are nine main groups and the element hydrogen, which is unique.

1. HYDROGEN Hydrogen makes up 90 per cent of all the matter in the Universe. Pure hydrogen is an invisible gas on Earth. It is not considered part of any one group. Hydrogen powers the nuclear reactions inside stars, including our Sun, and is found on Earth in the compound H2O or water.
2. ALKALINE-EARTH METALS Alkaline-earth metals react with water and are found in minerals in Earth’s crust. In pure form, they are silvery-white. They are similar to alkali metals, but less reactive. Calcium, found in chalk, milk, and bones, is a member of this group.
3. ALKALI METALS Sodium, contained in salt, is an alkali metal. These elements are characterized by their vigorous reaction with water. On contact, they will zoom all over the water’s surface or even explode. Alkali metals are not found in a pure form in nature because they react so strongly with water.
4. TRANSITION METALS This group is the largest and includes iron, silver, gold, nickel, platinum, and titanium. Transition metals are considered typical metals - they are hard and shiny, conduct electricity and heat well, and have high melting points.
5. ACTINIDES The elements in this group are radioactive metals mostly created synthetically in nuclear reactors or nuclear explosions. They have unstable atoms that break up and give out radiation particles. Uranium and plutonium are examples of actinides.
6. LANTHANIDES These soft, reactive metals were known as rare earths, because they were wrongly believed to occur only scarcely in nature. Silvery-white in appearance, they tarnish easily on contact with air. Holmium, the element with the greatest magnetic strength, is in this group.
7. NON-METALS Around one-sixth of elements are non-metals. They are poor conductors of electricity and melt at low temperatures. Carbon, nitrogen, and oxygen are all examples of non-metals, as are the halogens, a group of highly reactive elements that combine with other elements to form salts.
8. NOBLE GASES There are seven noble gases - also called rare or inert gases because they do not readily react with anything or combine with other elements to make compounds. They are helium, neon, argon, krypton, xenon, radon, and oganesson, although the latter may be a solid at room temperature.
9. POOR METALS Metals that are fairly soft and melt easily are known as poor metals. They are readily found as ores (minerals) in Earth and can be very useful, especially when made into alloys (two metals mixed together to make a harder metal). Aluminium and lead are both poor metals.
10. SEMI-METALS These elements have some properties of metals and some of non-metals. Arsenic, for example, is shiny like a metal, but not a good conductor. Some semi-metals are semiconductors, behaving as conductors or insulators depending on what other substances are added to them.

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MOLECULES

An element is a substance made of only one kind of atom. Atoms join, or bond, to other atoms of the same element, or to atoms of other elements. They do this by sharing or exchanging electrons. In many cases, the bonded atoms form groups called molecules. When atoms of one element combine with atoms of other elements, they form compounds.

• ETHANOL (C2H5OH) Ethanol is a compound with molecules containing two carbon (C) atoms, six hydrogen (H) atoms, and one oxygen (O) atom. At room temperature, it is a colourless liquid used as a disinfectant, preservative, and the alcohol in drinks.
• OXYGEN (O2) Some elements can bond in several ways to form different substances. Atoms of the element oxygen (O) bond together in pairs to form molecules of oxygen gas. High in the atmosphere, however, oxygen atoms also bond in threes to form the gas ozone.
• VITAMIN C (C6H8O6) Like ethanol, vitamin C (ascorbic acid) contains carbon (C), hydrogen (H), and oxygen (O) atoms. However, because the molecule contains different quantities of the elements arranged in a different way it forms an entirely different substance - a compound that is solid at room temperature.
• METHANE (CH4) Molecules of the gas methane contain four hydrogen (H) atoms bonded to a carbon (C) atom. Compounds of carbon and hydrogen are called hydrocarbons. They include fuels, such as methane, oil, and coal, and artificial materials, such as polystyrene.
• SALT (NaCl) Table salt, or sodium chloride, is made of equal numbers of sodium (Na) and chlorine (CI) atoms. Salt does not form as small individual molecules containing one atom each of sodium and chlorine. Instead, many atoms of the two elements link to form a rigid lattice called a crystal.
• WATER (H2O) When two atoms of the gas hydrogen (H) bond with one atom of the gas oxygen (O), they form molecules of liquid water. Water is the most common compound on Earth and is essential for life.
• SULFUR (S8) Eight atoms of sulfur (S) bond together in a ring to form a sulfur molecule. Most non-metal elements are gases at room temperature, but sulfur is a brittle, yellow solid.
• AMMONIA (NH3) The colourless gas ammonia is made up of one nitrogen (N) atom bonded to three hydrogen (H) atoms. Plants get the nitrogen they need to grow from ammonia and other nitrogen compounds within the soil.
• DIAMOND (C) A diamond can be thought of as a single giant molecule. It is formed from atoms of carbon (C) bonded in a strong crystal lattice. However, if carbon atoms join in flat sheets of hexagonal tiles, they form graphite, a brittle substance used to make pencil leads.

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