 # 4S1 Monday, 14/2/2011 10.45 – 11.55 am. Previously…

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4S1 Monday, 14/2/2011 10.45 – 11.55 am

Previously…

Relationship of Number of Particles and Number of Moles Number of moles = Number of particles N A Number of particles = Number of moles × N A Number of moles (mol) Number of particles × N A ÷ N A

Molar mass =The mass of one mole of a substance Unit:g mol -1

One mole of any substance contains 6.02x10 23 particles. Therefore, the molar mass of a substance contains 6.02x10 23 particles of the substance

RAMMolar mass Valuerefer Periodic Table Same as RAM UnitNo unitg mol -1 RAM vs Molar mass

ElementRelative mass Molar mass Helium44 g mol -1 Sodium2323 g mol -1 Water, H2O2(1) + 16 = 1818 g mol -1 Ammonia, NH 3 14 + 3(1) = 1717 g mol -1 Sodium chloride, NaCl 23 + 35.5 = 58.5 58.5 g mol -1 Lithium oxide, Li 2 O 2(7) + 16 = 30 30 g mol -1

ElementRelative massMolar mass FeSO 4 K2OK2O Al(OH) 3 NaNO 3 MgCO 3 56 + 32 + 4(16) = 152 152 g mol -1 2(39) + 16 = 9494 g mol -1 27 + 3(16 + 1) = 7878 g mol -1 23 + 14 + 3(16) = 85 84 g mol -1 24 + 12 + 3(16) = 84 85 g mol -1

Relationship of Mass and Number of Moles Number of moles = Mass Molar mass Mass = Number of moles x Molar mass Number of moles (mol) Mass (g) × Molar mass (g mol -1 ) ÷ Molar mass (g mol -1 )

Example 1 Find the number of moles of 22.1 g of AgNO 3 Molar mass of AgNO 3 = [108 + 14 + 3(16)] g mol -1 = 170 g mol -1 Number of moles of AgNO 3 = mass of AgNO 3 molar mass of AgNO 3 = 22.1 g 170 g mol -1 = 0.13 mol

Example 2 Find the number of moles of 4.55 g of B 2 O 3 Molar mass of B 2 O 3 = [2(11) + 3(16)] g mol -1 = 70 g mol -1 Number of moles of B 2 O 3 = mass of B 2 O 3 molar mass of B 2 O 3 = 4.55 g 70 g mol -1 = 0.065 mol

Example 3 Find the mass of 0.86 mol of MgCl 2 Molar mass of MgCl 2 = [24 + 2(35.5)] g mol -1 = 95 g mol -1 Mass of MgCl 2 = number of moles of MgCl 2 × Molar mass of MgCl 2 = 0.86 mol × 95 g mol -1 = 81.7 g

Example 4 Find the mass of 0.13 mol of C 2 H 4 Molar mass of C 2 H 4 = [2(12) + 4(1)] g mol -1 = 28 g mol -1 Mass of C 2 H 4 = number of moles of C 2 H 4 × Molar mass of C 2 H 4 = 0.13 mol × 28 g mol -1 = 3.64 g

Exercise 1 Find the number of moles of 23 g of NO 2 Molar mass of NO 2 = [14 + 2(16)] g mol -1 = 46 g mol -1 Number of moles of NO 2 = mass of NO 2 molar mass of NO 2 = 23 g 46 g mol -1 = 0.5 mol

Exercise 2 Find the mass of 0.1 mol of SO 3 Molar mass of SO 3 = [32 + 3(16)] g mol -1 = 80 g mol -1 Mass of SO 3 = number of moles of SO 3 × Molar mass of SO 3 = 0.1 mol × 80 g mol -1 = 8.00 g