Compounds and Mixtures KS3 Chemistry Compounds and Mixtures

Compounds and Mixtures Contents Compounds and Mixtures Comparing elements and compounds Compound names and formulae Word equations Mixtures Summary activities

Properties of elements and compounds Why is it safe to put sodium chloride on fish and chips… …but not safe to use sodium and chlorine?

Atoms in elements and compounds Elements are materials made up of one type of atom only. The element, hydrogen, exists as molecules. Each hydrogen molecule is made up of two hydrogen atoms joined together. H Compounds contain two or more different types of atom. The compound, water, exists as molecules. Each water molecule consists of two hydrogen atoms joined to one oxygen atom.

Element or compound?

Making a compound – water A compound is made when atoms of different elements react and join together. For example, water is produced from the chemical reaction between hydrogen and oxygen. hydrogen oxygen water + H O + H Two hydrogen molecules react with one oxygen molecule to produce two molecules of water. Why does water have different properties to its elements?

Properties of a compound – carbon dioxide A compound has different properties to the elements from which it is made because the atoms are joined differently. carbon oxygen carbon dioxide + Black solid used as fuel. Colourless gas in which many substances burn. Colourless gas used in fizzy drinks and fire extinguishers. + + O C

A compound is not a mixture The atoms in a mixture of hydrogen gas and oxygen gas, which have not reacted with each other, look like this… The atoms in water, the compound made when hydrogen and oxygen react and their atoms become chemically joined to each other, look like this…

Compounds and Mixtures Contents Compounds and Mixtures Comparing elements and compounds Compound names and formulae Word equations Mixtures Summary activities

Naming simple compounds To name simple compounds of metals and non-metals: 1. Write down the name of the metal. 2. Write down the name of the non-metal, changing the ending of the word to “-ide”. What is the name of the compound made when the following elements combine? magnesium and oxygen magnesium oxide sodium and chlorine sodium chloride oxygen and iron iron oxide

Naming simple compounds What is the name of each compound formed by these metal and non-metal elements? nitrogen lithium sulphur zinc iodine nickel bromine aluminium oxygen tin chlorine sodium magnesium iron Name of compound Element 2 Element 1 iron sulphide magnesium nitride sodium chloride tin oxide aluminium bromide nickel iodide zinc sulphide lithium nitride

Naming further compounds Many compounds contain more than two elements. For compounds containing two elements plus oxygen, the ending of the other non-metal usually changes to “-ate”. Element 1 Element 2 Element 3 Name of compound nickel sulphur oxygen nickel sulphate magnesium nitrogen oxygen magnesium nitrate sodium nitrogen oxygen sodium nitrate copper sulphur oxygen copper sulphate aluminium bromine oxygen aluminium bromate

Composition of compounds A compound contains atoms from different elements that are chemically joined together. A compound always contains a particular amount of each element. It has a fixed composition. Compound names can get quite long and complicated, so the symbols of the elements are used as a shorthand. The symbols of the elements in a compound are combined to give the formula of the compound. What is the formula of carbon dioxide?

Writing a formula A formula uses the symbols of the elements in a compound. When there is more than one atom of each element, the number is always written after the symbol. carbon dioxide carbon atom = 1 CO2 formula = oxygen atoms = 2 water hydrogen atoms = 2 H2O formula = oxygen atom = 1 The formula shows the ratio of atoms in a compound.

TiO2 Li2O AlCl3 What is the formula? What is the formula of each of these compounds? (In a formula put the metal first as when naming a compound.) 1. Titanium oxide For every titanium atom there are two oxygen atoms. Formula = 2. Lithium oxide For every two lithium atoms there is one oxygen atom. 3. Aluminium chloride For every aluminium atom there are three chlorine atoms. TiO2 Li2O AlCl3

SiCl4 MnO2 Al2O3 What is the formula? What is the formula of each of these compounds? (In a formula put the metal first as when naming a compound.) 1. Silicon chloride For every silicon atom there are four chlorine atoms. Formula = 2. Manganese oxide For every manganese atom there are two oxygen atoms. 3. Aluminium oxide For every two aluminium atoms there are three oxygen atoms. SiCl4 MnO2 Al2O3

What is the ratio of atoms?

What does a formula show?

Compounds and Mixtures Contents Compounds and Mixtures Comparing elements and compounds Compound names and formulae Word equations Mixtures Summary activities

Writing a word equation A word equation can be used to describe any chemical reaction, i.e. any process in which atoms become joined in different ways. The steps for writing a word equation are: On the right-handside, put the name of the reactant(s). If there are two or more reactants, link them with a + sign. 2. In the middle, write down an arrow (). 3. On the right-handside, put the name of the product(s). If there are two or more products, link them with a + sign.

What is the word equation? Lead reacts with oxygen to form lead oxide. What is the word equation for this reaction? lead + oxygen  lead oxide Why is lead oxide so different to both lead and oxygen? The lead and oxygen don’t mix, they react to form lead oxide. This means that the lead and oxygen atoms in the product are joined differently to the atoms in the reactants .

What is the word equation? Write out word equations for the following chemical reactions. Limestone (calcium carbonate) is heated to make calcium oxide and carbon dioxide. Magnesium reacts with hydrochloric acid to make magnesium chloride and hydrogen. Methane is burnt to make carbon dioxide and water. calcium carbonate  calcium oxide +carbon dioxide magnesium + hydrochloric acid  magnesium chloride + hydrogen methane + oxygen  carbon dioxide + water

Compounds and Mixtures Contents Compounds and Mixtures Comparing elements and compounds Compound names and formulae Word equations Mixtures Summary activities

What is a mixture? A mixture contains two or more substances that are mixed together but have not reacted with each other. Sea water is a mixture of salts, water and other substances. A mixture is not the same as a compound: The proportions of the substances in a mixture are not fixed. The properties of a mixture are often an “average” of the properties of its ingredients (e.g. a mixture of a black and white powder is grey). 3. The substances in a mixture are just mixed, not chemically joined, and so it is usually quite easy to separate the ingredients (e.g. it is easy to get salt from sea water).

Element, compound or mixture?

Element, compound or mixture?

Separating immiscible liquids Liquids that do not mix are described as immiscible. Examples of immiscible liquids are water with oil and water with petrol. On a small scale, immiscible liquids can be separated by simply removing the top layer using a pipette. water oil oil water

Separating miscible liquids Liquids that do mix are described as miscible. Examples of miscible liquids are water with alcohol and petrol with kerosine. Miscible liquids can be separated by heating them to boiling. The components of the mixture have different boiling points and so will boil off at different temperatures. A condenser is used to recover the liquids as they boil off. This piece of apparatus is a tube that has cold water circulating around the outside. It cools down vapours and condenses them back to a liquid. Substances with low boiling points are collected first, while those with higher boiling points are collected later.

Distillation apparatus

Separating mixtures Mixture Wanted Method glass and water glass filter How can each mixture be separated? Mixture Wanted Method glass and water glass filter sea water salt evaporate sea water water distil cooking oil and water cooking oil pipette alcohol and water alcohol distil

Experiment to separate a mixture Reggie has been given a mixture of salt, sand and water. He needs to separate these three substances but cannot remember how, so Reggie needs your help! Write an experimental plan for Reggie to follow so that he will end up with the sand, salt and water in separate containers. Start your plan with a list of the equipment that is needed for separating this mixture. Then write a step by step plan that is easy for Reggie or anyone else to follow.

Compounds and Mixtures Contents Compounds and Mixtures Comparing elements and compounds Compound names and formulae Word equations Mixtures Summary activities

atom – The smallest particle that can exist on its own. Glossary atom – The smallest particle that can exist on its own. boiling point – Temperature at which a pure liquid becomes a gas. compound – Substance made up of two or more different types of atoms that are chemically joined together. element – Substance made up of only one type of atom. formula – The symbols and numbers that represent the ratio of different atoms in a substance. immiscible – Liquids which do not mix. miscible – Liquids which do mix. mixture – Two or more substances that are mixed but not chemically joined together.

Anagrams

True or false?

Plenary: Multiple-choice quiz