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CHAPTER 3: CHEMICAL FORMULAE & EQUATIONS

CHAPTER 3: CHEMICAL FORMULAE & EQUATIONS. The Mole & Volume of Gas. 4S1 Thursday, 24/2/2011 7.30 – 8.40 am. Previously…. Relationship of Mass and Number of Moles Number of moles = Mass Molar mass Mass = Number of moles x Molar mass. × Molar mass (g mol -1 ).

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CHAPTER 3: CHEMICAL FORMULAE & EQUATIONS

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  1. CHAPTER 3: CHEMICAL FORMULAE & EQUATIONS The Mole & Volume of Gas 4S1 Thursday, 24/2/2011 7.30 – 8.40 am

  2. Previously…

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

  4. Chemists determines the number of moles of any gas by measuring its volume as gases cannot be weighed • It was found that under the same temperature & pressure, equal volumes of all gases contain the same number of particles. Therefore, the concept of molar volume was introduced

  5. Molar volume = the volume occupied by one mole of gas Thus, the molar volume is also the volume occupied by 6.02×1023 particles of gas

  6. Molar volume of any gas is: • 22.4 dm3 mol-1 at STP • OR • 24 dm3 mol-1 at room conditions

  7. Refer Textbook page 37 Do correction for the unit of molar volume

  8. Relationship of Volume of Gas and Number of Moles Number of moles = Volume of gas Molar volume Volume of gas = Number of moles x Molar volume × Molar volume (dm3 mol-1) Volume of gas (dm3) Number of moles (mol) ÷ Molar volume (dm3 mol-1)

  9. REMINDER!!! SI unit of volume is dm3 & 1 dm3 = 1000 cm3

  10. Example 1 Find the number of moles of 6.72 dm3 of O2 at STP Number of moles of O2 gas = volume of O2 gas molar volume at STP = 6.72 dm3 22.4 dm3 mol-1 =0.3 mol

  11. Example 2 Find the number of moles of 560 cm3 of CO2 at room condition Number of moles of CO2 gas = volume of CO2 gas molar volume at room condition = 0.56 dm3* 24 dm3 mol-1 =0.0233 mol

  12. Example 3 Find the volume 1.5 mol of H2 gas at STP Volume of H2 gas = Number of moles of H2 gas × Molar volume at STP = 1.5 mol × 22.4 dm3 mol-1 = 33.6 dm3

  13. Example 4 Find the volume 0.4 mol of He gas at room conditions Volume of He gas = Number of moles of He gas × Molar volume at room condition = 0.4 mol × 24 dm3 mol-1 = 9.6 dm3

  14. Exercise 1 Find the number of moles of 896 cm3 of HCl gas at STP Number of moles of HCl gas = volume of HCl gas molar volume at STP = 0.896 dm3 22.4 dm3 mol-1 =0.04 mol

  15. Exercise 2 Find the volume 0.9 mol of N2 gas at room temperature Volume of N2 gas = Number of moles of N2 gas × Molar volume at RT = 0.9 mol × 24 dm3 mol-1 = 21.6 dm3

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