C5 - Revision Summary

A gas in the dry air that is a compound is carbon dioxide (CO2). Most molecular substances are gases because you only need a little bit of energy to overcome the weak forces between them.This means that they are usually gases. Covalent bonding is the sharing of electrons. It only occurs when non-metals bond to non-metals. Ethane= 6 Hydrogen & 2 Carbons The Earth's hydrosphere is all the water in the oceans, seas, rivers, lakes etc. The sea is 'salty' because the hydrosphere contains dissolved compounds many of which are ionic compounds such as salts. Solid ionic compounds form crystals because they form giant lattices. A single crystal of salt is one giant ionic lattice. Solid ionic compounds have high boiling points because all the ions are held together by strong ionic bonds. The force of attraction between the ions is strong and requires a lot of energy to overcome them. An ionic compound can conduct electricity when dissolved because when the compound is dissolved in water the ions are free to move.In a solid the ions are in a fixed position and are not able to move.For a substance to conduct electricity it must contain charged particles that are able to move. a) Zinc b) Zn2+ +2OH- ---> Zn(OH)2 (s) Fe2+ + 2OH- ---> Fe(OH)2 (s) a)Test for carbon dioxide bubble the gas through limewater. If the limewater turns cloudy the gas is carbon dioxide. b) Page 49 Test for sulfates: Add HCl (to remove carbonates, which give a false test.) Add barium chloride solution. The positive test is the formation of a white precipitate. Test for halides. a) Add nitric acid to remove carbonates (false results). Then add silver nitrate. b) A yellow precipitate if formed. The Earth's lithosphere is the crust and the top part of the mantle. Three abundant elements in the Earth’s lithosphere are Silicon, Oxygen, Aluminium. Every carbon atom in diamond forms a covalent bond to FOUR other carbon atoms which makes diamonds hard, and suitable for drilling. Graphite has free (spare) electrons (negative particles) which can move between the layers allowing it to conduct electricity. An ore is a rock that contains a large amount of a certain mineral. A metal that can be extracted by reducing its oxide with carbon is Iron (Iron is less reactive than carbon). Electrolysis is using electricity to split a compound. An electrolyte is the liquid which conducts electricity in the electrolysis process. Ionic crystals can act as electrolytes because when they are molten they conduct electricity as the ions are able to move. During electroylsis, at the negative electrode the positive aluminum ions gain electrons and are reduced. At the positive electrode the negative oxygen ions lose electrons and are oxidised. Oxidation is a loss of electrons, reduction is a gain of electrons. Page 108 Page 108 Metals are able to conduct electricity as the free electrons are able to move. For a substance to conduct electricity it must contain charged particles that are able to move. Metals have high melting and boiling points because the atoms in metals are held together by metallic bonds. The bonds take a lot of energy to break them. a) extracting metals - Uses lots of energy, scars the landscape, and destroys habitats. Also noise, dust and pollution. b) disposing of metals- Wastes valuable resources, uses energy, tales up large amounts of land. It’s a good idea to recycle metals because then we use less energy to make new ones, conserve resources and reduce the waste in landfills.