# Mass, Calculations + Analysis

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• Mass, Calculations + Analysis
• Mass of Atoms
• Relative mass of protons + neutrons is 1
• Atomic number = number of protons
• same as number of electrons
• Mass number = protons + neutrons in nucleus
• Isotopes version of same element with different number of neutrons
• Masses of Atoms and Moles
• Atoms too small to weigh
• use relative atomic mass
• Average value for isotopes of an element
• Ar
• Relative formula mass = all the relative atomic masses added up in a compound
• eg. The Mr of CaCl2
• Ar of Ca = 40
• Mr = 111
• Ar of Cl x 2 = 71
• Mr = 111
• Mr
• Percentages and Formulae
• Relative atomic mass of element in compound used to wok out percentage composition
• eg. Percentage of carbon in CO2
• Ar of C = 12
• Mr = 44
• Percentage = (12 / 44)x100
• 27.3%
• Ar o O x 2 = 32
• Mr = 44
• Percentage = (12 / 44)x100
• 27.3%
• Emperical formula is the symbol of the compound, ie. CH3 or CaCl2
• Work out with given masses or percentage composition
• eg. Emperical formula of hydrocarbon that contains 80% carbon
• Mass in 100 grams
• Carbon = 80
• Hydrogen = 20
• Divide mass by Ar
• 80/12 = 6.67
• 20/1 = 20
• Divide by smallest number
• 6.67/6.67 = 1
• 20/6.67 = 3
• Emperical formula =
• CH3
• Yield
• Tells you how much is made
• The percentage yield tells you the max amount that could be made
• calculated before reaction takes place
• percentage yield =
• amount of product / max amount
• maximum amount is calculated from the balanced equation
• In industry, high percentage yield needed
• Reduce waste  and pollution
• Gas Chromatography - C2
• Analysing a substance for addiitves or food colouring
• mass spectrometry