Chapter 3 Mole concept, Chemical Formula and Equation

Form 4 Chemistry

1. A. Relative Atomic Mass and Relative Molecular Mass Based on the theory of particles: particles are very small and discrete . A single atom is too small and light and cannot be weighed directly Thus, the mass of an atom is obtained by comparing it with another atom which is taken as a standard.

2. Which element is chosen as standard atom and why?

3. Carbon-12 is chosen as a standard because: Carbon exists as a solid at room temperature Carbon can be handled easily Carbon has an accurate mass

4. Relative atomic mass, RAM Meaning; The average mass of one atom of the element when compared with 1/12 of the mass of an atom of carbon-12.

5. Example: RAM of magnesium = 24 = 24 1/12 x 12 = magnesium is 24 times larger than carbon-12 ** THE VALUE OF NUCLEON NUMBER IN THE PERIODIC TABLE OF ELEMENT = RELATIVE ATOMIC MASS, RAM

6. Periodic table

7. Relative molecular mass, RMM Meaning; The average mass of one molecule when compared with 1/12 of the mass of an atom of carbon-12. Relative Molecular Mass, RMM = Average mass of one molecule 1/12 x the mass of an atom of carbon-12 Calculate RMM by adding up the relative atomic mass of all the atoms that present in the molecule

8. Carbon dioxide Relative molecular mass, RMM

9. Glucose Relative molecular mass, RMM

10. Relative formula mass, R F M Meaning; The average mass of an ionic substance when compared with 1/12 of the mass of an atom of carbon-12. Relative Molecular Mass, RMM = Average mass of an ionic substance 1/12 x the mass of an atom of carbon-12 Calculate RFM by adding up the relative atomic mass of all the atoms that present in the ionic compound

11. Relative formula mass, R F M Zinc chloride

12. Relative formula mass, R F M Aluminium sulphate

13. Relative formula mass, R F M Iron(III) oxide

14. Try this 1

15. Try this 2

16. one pair of shoes =??shoe one dozen of beer=?? beer One mole of atom=??? atom

17. 602000000000000000000000 particles (atom/molecule/ion) Avogadro constant,

18. The Mole and the Number of Particles The number of particles in matter is measured in mole . Definition: The amount of substance that contains as many particles as the number of atoms in exactly 12 g of carbon-12 Symbol of mole: mol

19. How many atoms are there in 12 g of carbon-12? = 6.02 × 10 23 The value of 6.02 × 10 23 is called the Avogadro constant or Avogadro number Avogadro constant, N A The number of particles in one mole of a substance

20. Point to note: One mole of any substance contains 6.02 × 10 23 particles 1 mol of atomic substance contains 6.02 × 10 23 atoms 1 mol of molecular substance contains 6.02 × 10 23 molecules 1 mol of ionic substance contains 6.02 × 10 23 ions

21. Relationship between the number of moles and the number of particles (atoms/molecules/ions) Number of moles, (mol) Number of particles (atoms, molecules, ions) × N A ÷ N A

22. Number of particles Moles N A

23. Example 1: A closed glass bottle contains 0.5 mol of oxygen gas, O 2 (a) How many oxygen molecules, O 2 are there in the bottle? oxygen atoms (b) How many are there in the bottle? [Avogadro constant: 6.02 × 10 23 mol -1 ]

24. a) The number of oxygen molecules, O 2 = 0.5 mol × 6.02 × 10 23 mol -1 = 3.01 × 10 23 molecules b) The number of oxygen atoms = 0.5 mol × 6.02 × 10 23 mol -1 × 2 = 6.02 × 10 23 atoms N umb er of particles Mo l es N A

25. N umb er of particles Mo l es N A

26. N umb er of particles Mo l es N A

27. The Mole and the Mass of Substances The mass of one mole of any substance is called molar mass Units: g mol -1 The molar mass of substances are numerically equal to relative mass

28. Element Relative mass Mass of 1 mol Molar mass Helium 4 4 4 g mol -1 Sodium 23 23 23 g mol -1 Water, H 2 O 2(1) + 16 = 18 18 18 g mol -1 Ammomia, NH 3 14 + 3(1) = 17 17 17 g mol -1

29. Relationship between the number of moles and the mass of a substance Number of moles, (mol) Mass (g) × molar mass ÷ molar mass

30. Mass (g) Moles RAM / RMM / RFM

31. Example 1: What is the mass of 0.1 mol 2.408 × 10 23 atoms of magnesium? of magnesium? [Relative atomic mass: Mg=24; Avogadro constant: 6.02 × 10 23 mol -1 ]

32. (b) The number of moles Mg atoms = 2.408 × 10 23 6.02 × 10 23 mol -1 = 0.4 mol Mass of Mg atoms = 0.4 mol × 24 g mol -1 = 9.6 g (a) Molar mass of Mg = 24 g mol -1 Mass of Mg = 0.1 mol × 24 g mol -1 = 2.4 g Mass (g) Mo l es RAM / RMM / RFM N umb er of particles Moles N A

33. Example 2: RMM of SO 2 = 32 + 2(16) = 64 Molar mass of SO 2 = 64 g mol -1 The number of moles = 16 g 64 g mol -1 = 0.25 mol Mass (g) Mo l es RAM / RMM / RFM How many moles of molecules are there in 16 g of sulphur dioxide gas, SO 2 ? [Relative atomic mass: O=16, S=32]

34. The Mole and the Volume of Gas

35. Relationship between the number of moles and the volume of gas Number of moles, ( mol ) Volume of gas ( dm 3 ) × molar volume ÷ molar volume

36. V olume (dm 3 ) Moles 22.4 dm 3 (STP) / 24 dm 3 (room condition)

37. volume of 1.2 mol What is the of ammonia gas, NH 3 at STP? [Molar volume: 22.4 dm 3 mol -1 at STP] Example 1: V o lu m e (dm 3 ) Mo l es 3 22.4 dm (STP) / 24 dm 3 (RC) The volume of ammonia gas, NH 3 = 1.2 mol × 22.4 dm 3 mol -1 = 26.88 dm 3

38. How many moles of ammonia gas, NH 3 are present in 600 cm 3 of the gas measured at room conditions? [Molar volume: 24 dm 3 mol -1 at room condition] Example 2: V o lu m e (dm 3 ) Mo l es 3 22.4 dm (STP) / 24 dm 3 (RC) The number of moles of ammonia gas, NH 3 = 600 cm 3 1000 = 0.6 dm 3 = 0.6 dm 3 24 dm 3 mol -1 = 0.025 mol

39. Relationship between the number of moles, number of particles, mass and the volume of gas

40. H 2 Symbol of hydrogen atom Shows that there are two hydrogen atom in a hydrogen gas, H 2 molecule

41. Symbol of hydrogen atom H 2 O Shows that there are two hydrogen atom in a water molecule Symbol of oxygen atom Shows that there are one oxygen atom in a water molecule

42. Compound can be represented by two types: Empirical formula - Chemical formula that shows the simplest ratio of the number of atoms of each element in a compound. 2. Molecular formula - Chemical formula that shows the actual number of atoms of each element found in a molecule of a compound

43. To determine empirical formula of magnesium oxide Burn magnesium with oxygen To determine empirical formula copper(II) oxide Use hydrogen to removed oxygen from copper(II) oxide Weigh mass of copper

44. Try this..

45. Qualitative aspect: Identify the reactant and product Physical states -

46. Quantitative aspect: - Ratio of substances involved -

47. Solving steps Step 1: Find the mole Step 2: Compare the mole ratio Step 3: Find the value