1 / 22

Chemistry in Action

Chemistry in Action. W Richards Worthing High School. Balancing equations. Sodium + water sodium hydroxide + hydrogen Na + H 2 O NaOH + H 2. O. Na. Na. H. H. H. H. H. O. Consider the following reaction:. +. +.

robert-contreras
Download Presentation

Chemistry in Action

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chemistry in Action W Richards Worthing High School

  2. Balancing equations Sodium + water sodium hydroxide + hydrogen Na + H2O NaOH + H2 O Na Na H H H H H O Consider the following reaction: + + This equation doesn’t balance – there are 2 hydrogen atoms on the left hand side (the “reactants” and 3 on the right hand side (the “products”)

  3. Balancing equations Sodium + water sodium hydroxide + hydrogen O O Na Na Na Na H H H H H H H H O O 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) We need to balance the equation: + + Now the equation is balanced, and we can write it as:

  4. Some examples Mg + O2 Zn + HCl Fe + Cl2 NaOH + HCl CH4 + O2 Ca + H2O NaOH + H2SO4 CH3OH + O2 MgO ZnCl2 + H2 FeCl3 NaCl + H2O CO2 + H2O Ca(OH)2 + H2 Na2SO4 + H2O CO2 + H2O 2 2 2 3 2 2 2 2 3 2 2 2 2 2 4

  5. Testing for carbon dioxide Gas Limewater Limewater turns milky/cloudy

  6. Adding acid to carbonates Calcium carbonate + hydrochloric acid calcium chloride + carbon dioxide + water CaCO3(s) + HCl(aq) CaCl2(aq) + CO2(g) + H2O(l) Carbonates are compounds containing carbon and oxygen. When an acid is added to a carbonate the carbonate starts to fizz. A gas called _________ _______ is produced. 2

  7. Flame tests

  8. Flame tests Compounds containing lithium, sodium, potassium, calcium and barium can be recognised by burning the compound and observing the colours produced: Lithium Red Sodium Yellow Potassium Lilac Calcium Brick red Barium Green

  9. Metal ions Calcium is in group 2 and has two electrons in its outer shell, so it will form a Ca2+ ion. Chlorine is in group 7 so a chloride ion will be Cl- Metal compounds in a solution contain metal ions. For example, consider calcium chloride: Calcium chloride has the formula CaCl2

  10. Metal ions and precipitates Ca2+(aq) + OH- Ca(OH)2 (s) Some metal ions form precipitates, i.e. an insoluble solid that is formed when sodium hydroxide is added to them. Consider calcium chloride: 2

  11. Metal ions and precipitates Ca2+(aq) + OH- Ca(OH)2 (s) Some metal ions form precipitates, i.e. an insoluble solid that is formed when sodium hydroxide is added to them. Consider calcium chloride: 2

  12. Testing for chloride and sulphate ions For each test state: 1) The colour of the precipitate 2) What compound it is Test 1: Chloride ions Add a few drops of dilute nitric acid to the chloride ion solution followed by a few drops of silver nitrate. Precipitate formed = silver chloride (white) Test 2: Sulphate ions Add a few drops of dilute hydrochloric acid to the sulphate ion solution followed by a few drops of barium chloride. Precipitate formed = barium sulphate (white again)

  13. Ammonium, nitrate, bromide and iodide ions Ammonium ions: Add sodium hydroxide and test the gas using damp litmus paper – ammonia gas turns damp litmus paper blue. Nitrate ions: Add sodium hydroxide followed by aluminium powder and test using damp litmus paper. Bromide and iodide ions: Add a few drops of dilute nitric acid followed by a few drops of silver nitrate solution. A pale yellow precipitate should be formed for bromide ions and a darker yellow precipitate for iodide ions.

  14. Thermal decomposition Copper carbonate: CuCO3 (s) CuO(s) + CO2 (g) (Green – Black) Zinc carbonate: ZnCO3 (s) ZnO(s) + CO2 (g) (White – Yellow) A “thermal decomposition” reaction occurs when a compound breaks down (“decomposition”) through the action of heat. • Practical work: • Perform a thermal decomposition reaction on each of these compounds and state: • The colour changes you observed • The reaction that happened

  15. Sulphuric acid Sulphur + oxygen sulphur dioxide Sulphur dioxide + oxygen sulphur trioxide Sulphur trioxide + conc. sulphuric acid oleum Oleum + water sulphuric acid Sulphuric acid has many important uses – car batteries, detergents, fertilisers etc. How sulphuric acid is made: Step 1: Burn sulphur in air: Step 2: Pass the sulphur dioxide over a vanadium oxide catalyst at 450OC: Step 3: Dissolve the sulphur trioxide in sulphuric acid: Step 4: Add water to the oleum:

  16. Reversible Reactions A + B C + D Endothermic reactions Exothermic reactions Increased temperature: Increased temperature: A + B C + D A + B C + D Decreased temperature: Decreased temperature: A + B C + D A + B C + D When a reversible reaction occurs in a CLOSED SYSTEM (i.e. no reactants are added or taken away) an EQUILIBRIUM is achieved – in other words, the reaction goes at the same rate in both directions: More products Less products Less products More products

  17. Sulphuric acid Endothermic 2SO2 + O2 2SO3 Exothermic Step 2 in the manufacture of sulphuric acid is an example of a reversible reaction: What would happen if the temperature was decreased? The reaction would favour the production of sulphur trioxide BUT the reaction would happen at a slower rate. Solution – use 450OC as a compromise

  18. Iron and Steel The iron contains roughly 5% carbon and different metals and is very ________. In order to reduce these impurities and convert the iron into _________ the molten iron is transferred into another furnace where it is mixed with recycled scrap iron and pure ___________. The oxygen reacts with the metal impurities to form ________ oxides. Calcium carbonate is also added to remove some of the acidic oxides as _______ when the furnace is tilted. Words – slag, brittle, steel, oxygen, acidic In previous work we considered the role of the blast furnace in extracting iron from its ore.

  19. Making steel – the reactions Silicon + oxygen Silicon oxide Calcium carbonate calcium oxide + carbon dioxide Silicon oxide + calcium oxide calcium silicate Steel with chromium and nickel is called stainless steel Steel with a high carbon content is strong but brittle Steel with a low carbon content is easily shaped 1) Mixing oxygen with silicon impurities: 2) Decomposition of limestone: 3) Adding these products together:

  20. Titanium Titanium chloride + sodium titanium + sodium chloride In this reaction the titanium is displaced my a more reactive metal. This reaction is done in an argon atmosphere to avoid any further reactions. Titanium ions have a charge of 4+ and gain four electrons to become titanium atoms. This is a reduction reaction. Titanium is a strong metal used in planes, replacement hip joints, bikes etc. Two steps are used in its manufacture: Step 1: Convert titanium dioxide (ore) to titanium chloride Step 2: Displace the titanium using sodium or magnesium:

  21. Aluminium ++++ ---- Al H2SO4 Aluminium is a fairly reactive metal that doesn’t corrode due to forming a thin layer of aluminium oxide. This explains why greenhouses don’t rust and don’t need to be painted. A thicker layer of aluminium oxide can be made artificially. There are two stages: 1) Remove the natural layer by placing the aluminium in sodium hydroxide. 2) Use electrolysis on sulphuric acid with the aluminium as the positive electrode. This is called anodising.

  22. Electroplating ++++ ---- Silver electrode Object to be plated Solution containing silver ions

More Related