Further Calculations

- The relative atomic mass is defined as follows : The weighted average of all the element's natural isotopes on a scale where the mass of Carbon-12 is exactly 12.- The relative atomic mass of an element or the relative formula mass of a compound is always equal to the mass of one mole of the substance in grams.- A mole of a substance is defined as being 6.02*10^23 atoms/molecules of that substance. - The molar volume of any gas is always the same and one mole of gas occupies 24dm^3 or 24000cm^3.- Empirical formulae are the most simple ratio of atoms of each element in a compound, while the molecular formula gives the actual numbers of each element in a compound. For instance, the molecular formula for Hydrogen Peroxide is H2-O2, while its empirical formula is H-O.- To work out the relative molecular mass of compund, simple add the relative atomic mass of its constituent elements. For instance, the Mr of H2-O is the 2 lots of the Ar of Hydrogen (1*2=2) plus 1 lot of the Ar of Oxygen (1*1=1).

An Overview

Moles

- To work out the number of moles of moles in a certain mass of a known substance, simply divide the mass of the substance by its Ar/Mr. - To work out the mass of a certain number of moles of a known substance, simply multiply the number of moles of the substance with the Ar/Mr.- To work out the Ar/Mr of an unknown mass of a substance, and knowing the moles, simply divide the mass of the substance with the number of moles of that substance. FOR THE FOLLOWING, THE VOLUME AND MOLAR MUST USE THE SAME MEASUREMENT!!!- Molar Volume = 24dm^3 or 24000cm^3 at 1atm and at 25C- To work out the number of moles in a certain volume of a known gas, simple divide the volume by the Molar Volume.- To work out the volume of a certain known gas, simply multiply the number of moles of the gas with the Molar Volume.                        - You don't need to work out Molar Volume as it is constant!                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  

Percentage Yields

- Percentage Yield is a measure of the efficiency of a chemical reaction.- Theoretical Yield is how much of a product you should get.*- Experimental Yield is how much of a product you do get.**You can measure this in mass or moles, but you must be consistent.- To work out the Percentage Yield simply divide the Experimental Yield by the Theoretical Yield and then multiply the answer by 100, making the answer a percentage.-  To work out the Experimental Yield simply multiply the Percentage Yield with the Theoretical Yield and then divide the answer by 100.- To work out the Theoretical Yield simply multiply the Experimental Yield by 100 then divide the answer by the % yield.