1.d Relative formula masses and molar volume of gases

1.16 and 1.19 Calculate relative formula masses (Mr)

IN CGP The relative formula mass of a molecule, Mr, can be worked out by adding up the relative atomic masses, Ar, of the atoms in the molecule. Example, calculate the relative formula mass of Magnesuium nitrate, Mg(NO3)2 , where Ar:Mg = 24 and Ar:N = 14 (Note that 3 and 2 are subscript. I can't do in computer) Mr = 24 (14 + 16 + 16 + 16) 2 = 24 + (62)2 =24+124 =148

1.20 Formula to convert gas volues into moles

moles = (volume in cm^3) / 24,000)

Volume units

1 litre = 1 dm^3 = 1,000 cm^3 1 cubic meter = 1,000 dm ^3 Note dm: decimeter

1.17 mole represent the amount of substance

A mole is 6x10^23 things. You can have a mole of jelly beans (as big as the whole earth!) A mole of atoms, i.e. 6x10^23 atoms. A mole of atoms fits in a little dish! That shows you how small are atoms

1.18 Mole as the Avogadro number of particles in a substance

A mole is an amount of substance. It is a very large number, approximately 6x10^23. This number is called the Avogadro number or constant

Avogrado's law

Equal volumes of gases at the same temperature and pressure contain equal number of molecules.

Example, An airship contained 180,000 cubic metres of hydrogen. What is the mass of this hydrogen? Ar:H = 1

Number of moles = Volume dm^3 /24 dm^3 Number of moles H2 = 180,000,000 /24 = 7,500,000 mol Each mole of Hydrogen weighs 2g Mass of Hydrogen = 7,500,000 x 2 = 15,000,000 g

1.16 What is relative formula mass

The relative formula mass tells you the mass of a mole of that substance. For example, a mole of sodium chloride , NaCl, has a relative formula mass of 58.5, so le mole has a mass of 58.5 g.

1.20 Use molar volume (24 Dm^3 and 24,000 cm^3) at room temperature and pressure (rtp) in caculations.

The volume occupied by 1 mole of a gas is called the molar volume. T Equal volumes of ALL gasses taken at the SAME TEMPERATURE (25C) and pressure (1 atmosphere) contain the Avogadro number of molecules. The volume occupied by 1 mole of ANY gas is approximately 24,000 cm^3 (24 dm^3) at rtp

1.20 Molar value of a gas

The volume of one mole of any gas contains the Avogrado constant number of molecules of that gas. Volume, instead weight, is used in gases because it is difficult to weight gases.

rtp

rtp is an abbreviation used for 'room temperature and pressure'