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Chapter 5 chemical changes

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Chapter 5 chemical changes

  1. 1. ENERGY AND CHEMICAL CHANGES
  2. 2. Have you noticed that a matter can change? There are two types of changes,  physical changes  chemical changes
  3. 3. a) Physical change only involves a change of physical properties (shape or appearance) No change in chemical properties Small amount of energy required Physical change Reversible No new substances
  4. 4.  boiling water,  dissolving sugar in water,  mashing potato  water cycle.
  5. 5. b) Chemical change is a change which produces substances which have different chemical properties from the original substances Change in chemical properties A lot of energy required Chemical change Irreversible New substances are formed
  6. 6.  rusting of iron  burning of kerosene  frying egg  photosynthesis  raising cake batter  souring milk
  7. 7.  Section A: potassium iodide and lead(II)nitrate solution
  8. 8.  Section water B: Copper(II)sulphate crystals and
  9. 9.  Endothermic reactions
  10. 10.  Exothermic reaction
  11. 11.  Aim: to study exothermic and endothermic reactions  Hypothesis: different types of chemical reactions cause different changes in temperature  Variables: constant variables: volume of distilled water manipulated variable: type of substance responding variable: final temperature  Materials and apparatus:sodium hydroxide, Ammonium chloride, distilled water, test tube, thermometer, spatula
  12. 12.  Steps: 1. 5cm³ of distilled water was filled into a test tube 2. the initial temperature of distilled water was recorded. 3. a few sodium hydroxide were added into the test tube using a spatula. 4. the mixture was stirred until the sodium hydroxide dissolved. 5. the final temperature was recorded in the table. 6. the outer wall of the test tube was touched. 7. the experiment was repeated using ammonium chloride powder.
  13. 13.  Reaction of metals with water the reaction metals with water will produce hydrogen gas and alkaline solution metal + water hydrogen gas + alkaline solution for example, sodium + water hydrogen gas + sodium hydroxide different metals, give different reaction with water
  14. 14.  Reaction of metals with acids metals react with acids to produce salt and hydrogen gas metal + acid salt + hydrogen gas for example, magnesium + hydrochloric acid magnesium chloride + hydogen gas
  15. 15.  Results: Type of substances Initial Final Change in Outer temperature temperature temperature wall of /ºC /ºC /ºC test tube Sodium hydroxide 29 crystals with distilled water 48 19 Hot Ammonium 29 28 -1 Cold chloride powder with distilled water  Analysis: 1. sodium hydroxide is the substance that increase the water temperature because it released heat (exothermic reaction) 2. ammonium chloride is the substance that decrease the water temperature and absorbed heat (endothermic reaction)  Conclusion: Hypothesis is accepted. Different types of chemical reactions cause different change in temperature.
  16. 16.  Reaction - of metals with oxygen Metals produce metal oxide when heated in oxygen gas Metal + oxygen metal oxide For example, aluminium + oxygen aluminium oxide
  17. 17. To fix the position of the potassium manganate (VII) crystals at its place To provide oxygen
  18. 18.  Results: a) Aluminium b) Zinc
  19. 19. c) Copper d) Magnesium
  20. 20.  If carbon can remove oxygen from its metal oxide, so carbon is more reactive than that metal
  21. 21.  Results: Mixture Observation Reaction Carbon + lead(II)oxide Mixture glows (menyala) yes Carbon + aluminium oxide No change no Carbon + zinc oxide Mixture glows slowly (menyala perlahan) yes  Analysis:  Conclusion:  Reflection: Comparison of reactivity
  22. 22.  Importance of the reactivity series of metals 1. Reaction of a metal - predict reactions which involve metals 2. Displacement of metal from a solution 3. Displacement of metal from an oxide 4. Extraction of metal using carbon 5. Terminal of a simple cell
  23. 23.  Positions of Metals in the Reactivity Series and Methods of Extractions Metal Increase in reactivity Method of extraction Potassium Sodium Calcium Magnesium Aluminium Electrolysis of the molten ore •Metals that are more reactive than carbon •Extracted by flowing of electric current through the molten metal oxide CARBON Zinc Iron Tin Lead Heating mixtures of ore and carbon •Metals that are less reactive than carbon •Heating metal ores with carbon (coke) Copper Mercury Heating ore (metal sulphides) in air Silver Gold Exist as free elements in the ground
  24. 24.  Extraction of Metals from Their Ores Metal ore (example: tin and iron) •Coke (type of carbon) •Limestone (eliminate impurities to form slag) (Carbon dioxide) •Tin oxide + carbon tin + carbon dioxide •Iron oxide + carbon iron + carbon dioxide
  25. 25. The process of using electrical energy to decompose a molten or an aqueous (watery) solution of an ionic compound.  Electrolysis involves the movement of ions.  Positive carbon electrode(+) Anion (negative ion) Cation (positive ion) Negative carbon electrode(-)
  26. 26. •Lead (+) : grey •Bromine (-) : brown
  27. 27. 1. Metals extraction - Metals that are more reactive than carbon are extracted from the ores.
  28. 28. 2. Metal purification - Impure metal is used as the anode while pure metal used as cathod - Electrolyte is the salt solution
  29. 29. 3. Metal electroplating - An object can be electroplated with a metal. - The metal is used as the anode while the object is used as the cathode. (ANODE) (Object to be plated/ CATHODE)
  30. 30.  Aim: to study the electroplating of objects made of iron with copper  Hypothesis: copper deposites as a thin layer on the iron nail  Variables: a) Constant variable: b) Manipulated variable: c) Responding variable:  Materials and apparatus:
  31. 31. Steps: 1. A beaker was filled with copper(II)sulphate solution. 2. The apparatus for the electrolysis was set up as shown in diagram. 3. The copper plate was used as the anode whereas the iron nail was used as the cathode. 4. The switch was turned on and a current of 0.5A flowed through the circuit for 10 minutes. 5. The switch was turned off and the iron nail was taken out. 6. Observation of the products at both electrodes were recorded. 
  32. 32. (Iron nail)
  33. 33.  Results: Metal  Analysis: Observation  Conclusion: The copper plate becomes thinner Copper Iron nail A brown solid is deposited
  34. 34.  - - - Simple Cell Consists of two electrodes (different metals) The electrolyte can be a salt solution, a diluted acid or a diluted alkali. The more reactive metal electrode acts as the negative terminal The less reactive metal electrode acts as the positive terminal Chemical energy to electrical energy V
  35. 35.  Result: a) Zinc and Copper b) Copper and copper
  36. 36.  Dry - cell Easy to carry and supply constant current Cannot be recharged and not long lasting
  37. 37.  Lead-acid - accumulator 6 lead-acid cells connected in series 12 V (high voltage) Car battery (heavy & electrolyte is easy to spills over )
  38. 38.  Alkaline - battery Different electrolyte with dry cell Long-lasting & higher current than dry cell Cannot be recharged & expensive
  39. 39.  Mercury - cell/ zinc-silver oxide battery 1.2 V Long-lasting & supply constant current Cannot be recharged
  40. 40.  Nickle-cadmium - battery Same principle as an accumulator but uses different substances Long-lasting, can be recharged
  41. 41.  Example of chemical reactions which require light is photosynthesis  Change light energy to chemical energy
  42. 42. Photographic film contains photosensitive coatings made up of silver bromide.  Photosensitive substances are substances that undergo chemical change when exposed to light. 
  43. 43.  The silver bromide decomposes to black silver metal and bromine gas when exposed.  The exposed area produces opaque area.  Silver bromide silver + bromide
  44. 44.  Covered with thumb  Exposed to light

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