Element, Compound and MIXTURE SELF-TEST Which of the pictures shows a model of an element? What is an element? Where are all the elements listed?

two elements The Periodic Table lists all the elements. An element contains one type of atom only. It is a simple substance that cannot be split into simpler substances by chemical means. two elements

Which of the pictures above represent an ELEMENT? There are five! j h d e f g i Which of the pictures above represent an ELEMENT? There are five! see next page for answers

Answer : a,e,f,g and j are all elements, because the particles in them are identical (The same size and colour.) b,c,d,h and i are compounds. The picture below shows an experiment to find the percentage of oxygen in the air. gas syringe copper turns to copper oxide

Copper metal is heated in 100 cm3 of air. What do you see happening to the copper? What happens to the volume of air in the syringes and why? Can you write an equation for the reaction that happens?

The copper turns from coppery pink to black. This is because the copper reacts with oxygen in the air and turns to black copper oxide The volume of air in the syringes changes from100cm3 to 79cm3. This is because all the oxygen in the air joins to the copper and so the volume of air that remains is everything that is not oxygen. If 79% is not oxygen, then 21% of air is oxygen. copper + oxygen copper oxide

The Composition of Air can also be Determined using the rusting of Iron The iron is trapped in 50cm3 of air. As the iron rusts, the oxygen in the air joins to it. iron + oxygen iron oxide 21% of the air has been used up, so water rises up the tube by 21%. It then stops rising as there is no more oxygen to join to the iron. You must remember the percentages of 4 gases in air carbon dioxide 0.03-0.04%

a d b e c f The picture shows the laboratory preparation of oxygen. Can you name the pieces of equipment that are labelled? The answers are on the next page.

a d b e c f The laboratory preparation of oxygen. tap funnel b conical flask c delivery tube d gas jar e beehive shelf f trough The laboratory preparation of oxygen. Now name the two chemicals that are used. One generates the oxygen. The other is a catalyst - what is a catalyst?

Hydrogen peroxide generates the oxygen. Manganese (IV) oxide is the catalyst. A catalyst speeds up a chemical reaction but is not chemically changed itself in the process. Questions This method of collection is called DOWNWARDS DISPLACEMENT of WATER Why does the first gas jar collected contain very little oxygen? What is the test for oxygen?

The first gas jar contains most of the air that was in the flask to start with. so it contains very little oxygen The test for oxygen is that it relights a glowing splint.

Think of three Uses for Oxygen Remember that a use is something we might go out and buy some oxygen for, so just breathing will not do.

Possible Answers to Uses of Oxygen : 1. Making a hot flame for welding - oxy-acetylene welding. 2. Oxygen to assist breathing in hospitals. 3. Oxygen for breathing in space. 4. Oxygen to assist breathing under water. 5. Oxygen to assist breathing for firemen.

Here are four different elements burning in oxygen. 1 3 2 Here are four different elements burning in oxygen. Which is which? What products are formed? 4

4 2 2 2 2 2 1 2 3 1. Sulphur burning 2. Carbon burning sulphur + oxygen sulphur dioxide S + O2 SO2 2. Carbon burning carbon + oxygen carbon dioxide C + O2 CO2 3. Magnesium burning magnesium + oxygen magnesium oxide 4. Iron burning iron + oxygen iron oxide Some oxides are acidic and some are alkaline or basic. Which is which? 4

conduct electricity brittle conducts heat malleable shiny matt Metal oxides like magnesium oxide or iron oxide are alkaline or basic (red litmus turns blue). Non-metal oxides like carbon dioxide or sulphur dioxide are acidic (blue litmus turns red). You need to know the differences in physical properties between metals and non-metals. Sort the following into properties of metals and non-metals. does not conduct electricity variable colour conduct electricity brittle conducts heat malleable shiny silver not attracted to a magnet matt sonorous

a magnet except iron nickel and cobalt METAL NON-METAL conduct electricity variable colour malleable does not conduct electricity shiny brittle silver sonorous matt not attracted to a magnet not attracted to a magnet except iron nickel and cobalt conducts heat

Which of the pictures above represent a COMPOUND? j h d e f g i Which of the pictures above represent a COMPOUND? There are five! You must know the definition of a compound and a mixture. see next page for answers

A compound is made of two of more elements chemically combined together. A mixture is made of two or more substances not chemically combined together. The compounds are : Notice that they all have atoms (circles) that are different, joined to each other. They may be different in colour or size or both. h d b c i