Unit 1 Building Blocks

Menu To work through a topic click on the title. Substances Chemical Reactions Bonding Acids and Alkalis End

Substances

Safety Too avoid accidents we must be careful carrying out experiments. Most safety rules are only common sense.

Never put chemicals near your mouth. After using chemicals wash your hands before eating. All practical work must be done at the worktops. Do not sit on the worktops. Always wear safety goggles.

If there is any broken glass report it to your teacher so it can be cleared up properly. Be careful to leave the bunsen burner with a yellow flame if you are not using it.

When heating test tubes make sure that they are not pointed at anyone.

Hazards There are laws about using chemicals to help keep safe everyone who works with chemicals. Hazard warning labels are attached to dangerous chemicals. Hazard symbols are on road tankers to warn about dangers should the chemicals spill.

Each hazard which is toxic, corrosive, flammable, harmful or irritant is given a simple symbol which can be easily recognised. Here are some of these symbols.

Toxic

Corrosive

Flammable

Harmful

Irritant

Elements Everything in the world is made from about 100 elements. Each element has a name and a symbol. The symbol is usually one capital letter and one small letter e.g. Ca Chemists have arranged elements in the Periodic Table.

The Periodic Table The vertical columns are called groups. Elements in the same group of the Periodic Table show similar chemical properties.

Elements Many elements are solid at room temperature. Mercury and bromine are liquid at room temperature. 11 elements –hydrogen, nitrogen, oxygen, fluorine, chlorine, helium, neon, argon, krypton, xenon, radon - are gases at room temperature.

Elements can be classified as metals or non-metals. There are more metals than non- metals.

Many elements have everyday uses. Aluminium is used as kitchen foil. Carbon is used in pencil leads. Gold, silver and platinum are used in jewellery. Copper is used in electrical wiring.

Some elements, including gold, silver and copper, have been known for a long time. The most recently discovered elements have been made by scientists.

Mixtures Mixtures occur when two or more substances come together without reacting.

Air Air is a mixture of gases. Air is approximately 80% nitrogen and 20% oxygen. The test for oxygen is that it relights a glowing splint. The splint will not relight in air because there is not enough oxygen.

Compounds Compounds are formed when elements react together.

Compounds with a name ending in “ –ide “ contain the two elements named. Copper chloride contains copper and chlorine. Sodium oxide contains sodium and oxygen.

Compounds with a name ending in “ -ite “ or “ -ate “ contain the two elements named and the element oxygen. Copper carbonate contains copper, carbon and oxygen. Sodium sulphite contains sodium, sulphur and oxygen.

Solutions A solution is formed when a substance dissolves in a liquid. A substance which dissolves in a liquid is soluble. A substance which does not dissolve in a liquid is insoluble.

If we only dissolve a small amount of substance we make a dilute solution. If we dissolve a large amount of substance we make a concentrated solution. A solution is diluted by adding more liquid.

A saturated solution is one in which no more substance can be dissolved.

Substances Click here to repeat Substances. Click here to return to the Menu Click here to End.

Chemical Reactions

Chemical Reactions When a chemical reaction takes place one or more new substances are made. Burning a match is a chemical reaction because new substances are made. Melting ice is not a chemical reaction since ice is solid water.

How do we recognise a chemical reaction? A lot of chemical reactions occur in the world around us. When a chemical reaction takes place one of the following may happen a change in appearance a colour change a gas produced a precipitate formed. an energy change

How do we speed up a chemical reaction? Changes in particle size affects the speed of reactions, both in the laboratory and in our everyday life. Powders react more quickly than lumps. Mince will cook more quickly than stew.

Changes in temperature affect the speed of reactions, both in the laboratory and in our everyday life. Reactions take place more quickly at high temperatures. An egg will fry more quickly if we turn up the heat.

Changes in concentration affect the speed of reactions, both in the laboratory and in our everyday life. Increasing the concentration of the chemicals speeds up a reaction. Adding more bleach to water speeds up the whitening of cloth.

Catalysts A catalyst is a substance which speeds up a reaction and is not used up by the reaction. The exhaust system of a car contains a catalytic converter (containing platinum) to remove harmful gases from the exhaust.

Enzymes Enzymes are catalysts which affect living things. Enzymes are used to make: Yoghurt Cheese Medicines Beer

Uses of Enzymes EnzymeUse CelluloseMakes jeans more faded ZymaseChanges sugars to alcohol ProteaseUsed in washing powder to remove stains PapainMakes meat tender

Word Equations In a chemical reaction the substances which react together are called the reactants. The substances which are produced are called the products.

In a chemical equation we show the reactants and products, separated by an arrow, which means “change into”. Reactants  Products

In a word equation we use the names of the reactants and products. hydrogen + oxygen  water

Chemical Reactions Click here to repeat Chemical Reactions Click here to return to the Menu Click here to End.

Bonding

Atoms Every element is made up of very small particles called atoms. Atoms of different elements are different. Each element in the Periodic Table has a number called the atomic number.

The Periodic Table

Molecules

Some substances are made up of molecules. Molecules are made up of two or more atoms held together by strong bonds. Bonds between molecules are weak.

Ions

Some substances are made up of ions. Ions can be positively or negatively charged. Ionic compounds are made up of oppositely charged ions. Bonds between ions are strong.

Formulae A chemical formula uses chemical symbols to show the number and type of atom present. For example C 3 H 8 means that the molecule of this compound contains 3 carbon atoms and 8 hydrogen atoms.

We can write formulae by counting the atoms in a model or picture.

The name can tell us how many atoms are there. Mono- means 1 Di- means 2 Tri - means 3 Tetra- means 4

The name can tell us how many atoms are there. Mono- means 1 Di- means 2 Tri - means 3 Tetra- means 4

The name can tell us how many atoms are there. Mono- means 1 Di- means 2 Tri - means 3 Tetra- means 4

The name can tell us how many atoms are there. Mono- means 1 Di- means 2 Tri - means 3 Tetra- means 4

The name can tell us how many atoms are there. Mono- means 1 Di- means 2 Tri - means 3 Tetra- means 4

Bonding Click here to repeat Bonding Click here to return to the Menu Click here to End.

Acids and Alkalis

The pH scale The pH scale ranges from below O to above 14. Acids have a pH of less than 7 Pure water and neutral solutions have a pH equal to 7 Alkalis have a pH of more than 7.

To find the pH of solutions we can use: Universal indicator pH paper A pH meter

Acids and pH The lower the pH of an acid, the greater the acidity Diluting acids makes them less acid and so makes the pH lower.

Alkalis and pH The higher the pH of an alkali, the greater the alkalinity. Diluting alkalis makes them less alkaline, and so increases their pH.

Acids Acids are often used in the home, in industry and the laboratory. The common laboratory acids are hydrochloric acid, sulphuric acid and nitric acid. Some household acids are vinegar, lemonade, soda water and Coke.

Alkalis Alkalis are often used in the home, in industry and the laboratory. The common laboratory alkalis are sodium hydroxide, lime water and ammonia solution. Some household alkalis are baking soda, oven cleaner, dishwashing powder, bleach and soaps.

Neutralisation Neutralisation takes place when acid and alkali are mixed. When alkalis and acids react they form salt and water Acid + Alkali  Salt + Water The salt contains the metal from the neutraliser.

When carbonates and acids react they form salt, water and carbon dioxide. Acid + Carbonate  Salt + Water + Carbon dioxide The salt contains the metal from the neutraliser.

Neutralisation increases the pH of the acid up towards 7. Neutralisation decreases the pH of the alkali down towards 7. Everyday examples of neutralisation include reducing soil acidity, reducing acidity in lakes and treatment of indigestion.

Salts In neutralisations hydrochloric acid forms chloride salts sulphuric acid forms sulphate salts nitric acid forms nitrate salts.

Acid Rain Carbon reacts with oxygen to produce carbon dioxide. Sulphur reacts with oxygen to produce sulphur dioxide. Nitrogen reacts with oxygen to produce nitrogen dioxide. All of these oxides dissolve in water to form acid solutions.

Sulphur dioxide, produced by the burning of fossil fuels dissolves in water in the atmosphere to produce acid rain. Nitrogen dioxide, produced by the sparking of air in car engines dissolves in water in the atmosphere to produce acid rain.

Acid rain damages Buildings made from carbonate rock Structures made of iron or steel Soil Plant and animal life.

Acids and Alkalis Click here to repeat Acids and Alkalis. Click here to return to the Menu Click here to End.

The End Hope you found the revision useful. Come back soon!!