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# Chemical Equations and Stoichiometry

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1. 3 Chemical Equations and Stoichiometry 3.1 Formulae of Compounds 3.2 Derivation of Empirical Formulae 3.3 Derivation of Molecular Formulae 3.4 Chemical Equations 3.5 Calculations Based on Chemical Equations 3.6 Simple Titrations

2. 3.1 Formulae of Compounds

3. 3.1 Formulae of compounds (SB p.43) ratio of no. of atoms Formulae of compounds How can you describe the composition of compound X? 1st way = by chemical formula C?H?

4. 3.1 Formulae of compounds (SB p.43) carbonatoms Check Point 3-1 hydrogen atoms How can you describe the composition of compound X? 2nd way = by percentage by mass Compound X Mass of carbon atoms inside = …. g Mass of hydrogen atoms inside = …. g

5. 3.1 Formulae of compounds (SB p.44) Different types of formulae of some compounds

6. 3.2 Derivation of Empirical Formulae

7. 3.2 Derivation of empirical formulae (SB p.45) From combustion data • During complete combustion, elements in a compound are oxidized. • e.g. carbon to carbon dioxide, hydrogen to water, sulphur to sulphur dioxide • From the masses of the products formed, the number of moles of these atoms originally present can be found

8. 3.2 Derivation of empirical formulae (SB p.45) Example 3-2A Example 3-2B Check Point 3-2A The laboratory set-up used for determining the empirical formula of a gaseous hydrocarbon

9. 3.2 Derivation of Empirical Formulae (SB p.48) Example 3-2D Example 3-2C Check Point 3-2B From combustion by mass Composition by mass Empirical formula

10. 3.3 Derivation of Molecular Formulae

11. 3.3 Derivation of molecular formulae (SB p.49) What is molecular formulae? Molecular formula ? = (Empirical formula)n

12. 3.3 Derivation of Molecular Formulae (SB p.49) Example 3-3A Example 3-3B Molecular formula From empirical formula and known relative molecular mass Empirical formula Molecular mass

13. 3.3 Derivation of Molecular Formulae (SB p.51) Example 3-3C Check Point 3-3A Water of Crystallization Derived from Composition by Mass

14. 3.3 Derivation of Molecular Formulae (SB p.52) Example 3-3D Example 3-3E Check Point 3-3B Composition by mass Find composition by mass from formula Formula of a compound

15. 3.4 Chemical Equations

16. mole ratios Check Point 3-4 3.4 Chemical equations (SB p.53) Chemical equations a A + b B  c C + d D (can also be volume ratios for gases) Stoichiometry = relative no. of moles of substances involved in a chemical reaction

17. 3.5 Calculations Based on Chemical Equations

18. 3.5 Calculations Based on Equations (SB p.65) Example 3-5A Example 3-5B Calculations based on equations Calculations involving reacting masses

19. 3.5 Calculations Based on Equations (SB p.66) Example 3-5C Check Point 3-5 Example 3-5D Calculations based on equations Calculations involving volumes of gases

20. 3.6 Simple Titrations

21. 3.6 Simple titrations (SB p.58) Simple titrations Acid-base titrations Acid-base titrationswith indicators Acid-base titrationswithout indicators (to be discussed in later chapters)

22. 3.6 Simple titrations (SB p.59) Copper(II) sulphate solution Finding the concentration of a solution Copper(II) sulphate + solute Water solvent solution

23. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~50 cm3

24. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~50 cm3

25. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~50 cm3

26. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~50 cm3

27. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~50 cm3

28. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~50 cm3

29. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution 50 cm3 Solution A

30. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~50 cm3

31. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~50 cm3

32. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~50 cm3

33. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~50 cm3

34. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~50 cm3

35. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~50 cm3

36. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution 50 cm3 Solution B

37. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~100 cm3

38. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~100 cm3

39. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~100 cm3

40. 3.6 Simple titrations (SB p.69) Finding the concentration of a solution ~100 cm3

41. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~100 cm3

42. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution ~100 cm3

43. 3.6 Simple titrations (SB p.59) Finding the concentration of a solution 100 cm3 Solution C

44. 3.6 Simple titrations (SB p.59) 2 x the amount of solute Comment on the concentrations of solutions A, B and C ! Concentration of solution B is 2 times that of the concentrations of solutions A & B. contain the same amount of solute (same concentration) Concentrationis theamount of solutein aunit volume of solution.

45. 3.6 Simple titrations (SB p.59) Comment on the concentrations of solutions A, B and C ! no. of spoons no. of moles mass Concentrationis theamount of solutein aunit volume of solution.

46. 3.6 Simple titrations (SB p.59) Unit: mol dm-3 Molarity A way of expressing concentrations Molarity is the number of molesof solute dissolved in1 dm3 (1000 cm3) of solution. (M)

47. 3.6 Simple titrations (SB p.59) What does this mean? 1 dm3 contains 2 moles of HCl Example 3-6A Example 3-6B “In every 1 dm3 of the solution, 2 moles of HCl is dissolved.”

48. 3.6 Simple titrations (SB p.62) Example 3-6C Titration without an indicator By change in pH value

49. 3.6 Simple titrations (SB p.62) Example 3-6D Titration without an indicator By change in temperature

50. 3.6 Simple Titrations (SB p.65) in burette in conical flask Redox titrations 1. Iodometric titration I2(aq) + 2S2O32-(aq)  2I-(aq) + S4O62-(aq) brown colourless