Molar volume 1.1.6 Text Book : Pages 14 - 15 2008 SPECIFICATIONS
1.1.6 Moles and Gas Volumes Calculate the amount of substance in moles using gas volumes
24 dm3 One mole of different gases ONE MOLE OF ANY GAS OR VAPOUR OCCUPIES 24 dm3 . . . at room temperature and pressure rtp = room temperature and pressure (298K and 105 Pa) One mole of different gases
MOLAR VOLUME rtp = standard temperature and pressure (298K and 105 Pa) ONE MOLE OF ANY GAS OR VAPOUR OCCUPIES 24 dm3 at rtp 1. Calculate the volume occupied by 0.25 mols of carbon dioxide at rtp 1 mol of carbon dioxide will occupy a volume of 24 dm3 at rtp 0.25 mol of carbon dioxide will occupy a volume of 24 x 0.25 dm3 at rtp 0.25 mol of carbon dioxide will occupy a volume of 6 dm3 at rtp rtp = standard temperature and pressure (298K and 105 Pa) ONE MOLE OF ANY GAS OR VAPOUR OCCUPIES 24dm3 at room temperature and pressure
ONE MOLE OF ANY GAS OR VAPOUR OCCUPIES 24dm3 at rtp MOLAR VOLUME ONE MOLE OF ANY GAS OR VAPOUR OCCUPIES 24dm3 at rtp 1. Calculate the volume occupied by 0.25 mols of carbon dioxide at rtp 1 mol of carbon dioxide will occupy a volume of 24 dm3 at rtp 0.25 mol of carbon dioxide will occupy a volume of 24 x 0.25 dm3 at rtp 0.25 mol of carbon dioxide will occupy a volume of 6.0 dm3 at rtp 2. Calculate the volume occupied by 0.08g of methane (CH4) at rtp Relative Molecular Mass of CH4 = 12.0 + (4x1.0) = 16.0 Molar Mass of CH4 = 16.0 g mol-1 Moles = mass/molar mass 0.08g / 16.0 g mol-1 = 0.005 mols 1 mol of methane will occupy a volume of 24 dm3 at rtp 0.005 mol of methane will occupy a volume of 24 x 0.005 dm3 at rtp 0.005 mol of methane will occupy a volume of 0.12 dm3 at rtp that’s 120 cm3 ONE MOLE OF ANY GAS OR VAPOUR OCCUPIES 24dm3 at room temperature and pressure
MOLES = volume THE MOLAR VOLUME MOLAR volume CALCULATING THE NUMBER OF MOLES OF A SINGLE SUBSTANCE moles = vol / molar vol volume = moles x molar volume molar volume = volume / moles UNITS volume dm3 ( litres ) or cm3 molar volume 24 dm3 or 24,000 cm3 MOLES = volume MOLAR volume Volume dm3 MOLES x 24.dm3 COVER UP THE VALUE YOU WANT AND THE METHOD OF CALCULATION IS REVEALED
1.1.6 Tasks Write out these Key definitions Molar volume is . . . Examiner tip is . . . . Worksheets Questions : 1, 2, 3
1 24000 cm3 11 134.4 cm3 2 2400 cm3 12 216 cm3 3 12000 cm3 13 960 cm3 4 48000 cm3 14 2952 cm3 5 2880 cm3 15 55.2 cm3 6 81600 cm3 16 192000 cm3 7 2640 cm3 17 0.24 cm3 8 96 cm3 18 144000 cm3 9 240000 cm3 19 182.4 cm3 10 10800 cm3 20 72000 cm3 Volume dm3 MOLES x 24.dm3
1 8.33E-03 2 2.08E-02 3 4.17E-02 4 8.33E-02 5 9.75E-03 6 9.42E-03 7 1.07E-02 8 9 10 1.00E-01 11 2.92E-02 12 2.33E-01 13 9.17E-02 14 8.75E-03 15 3.33E-02 16 3.33E-03 17 8.30E-05 18 8.33E-01 19 1.75E-02 20 3.75E-02 0.00833 0.02083 0.0417 0.0833 0.00975 0.009417 0.0107 0.1 0.02916 0.233 0.0917 0.00875 0.0333 0.00333 0.000083 0.833 0.0175 0.0375 Volume dm3 MOLES x 24.dm3
Volume dm3 MOLES x 24.dm3 mass MOLES x Molar mass
dm3 MOLES x 24.dm3 MOLES x Molar mass Volume mass 1 1090 2 7050 3 85700 4 7490 5 701 6 670 7 3380 8 30000 9 2400000 10 180000 11 56000 12 30500 13 20300 14 16000 15 5260 16 2370 17 375 18 12000 19 26500 20 77100 Volume dm3 MOLES x 24.dm3 mass MOLES x Molar mass
dm3 MOLES x 24.dm3 MOLES x Molar mass Volume mass 1 159 2 64 3 80 4 71 28 7 30 8 58.1 9 32 10 27.9 11 34.03 12 16.97 13 38.02 14 27.98 15 43.97 16 31.92 17 210.96 18 36.48 19 81.12 20 128.06 Volume dm3 MOLES x 24.dm3 mass MOLES x Molar mass
Volume dm3 MOLES x 24.dm3 mass MOLES x Molar mass
So what is the molar volume of a gas ? . . rearrange and calculate ! Extension . . Why . . . Combined and ideal gas laws p V = n R T p is the pressure – Pa . . . that’s actually – 101,325 Nm-2 V is the volume – m3 . . . . that’s 100 x 100 x 100 cm3 n is the number of moles of gas – that just 1 T is the temperature measured in Kelvin – rtp is 298K R is the gas constant ( 8.314472(15) J K-1 mol-1 ) So what is the molar volume of a gas ? . . rearrange and calculate ! The unit can be cm3 or dm3
V = n R T p p V = n R T V = 8.314472 x 1 x 298 101,325 = 0.0244531 X1,000,000 ( convert to cm3) = 24, 453 cm3 That's about 24.5 dm3