CHAPTER 2 - ANALYSIS BY MASS

analysis based on the determination of mass is called gravimetric analysis
substances or mixtures containing a volatile component, such as water, are heated to drive of the volatile material and then the mass of the solid product left behind is measured
the substance must be heated until a constant mass is obtained to ensure that all the volatile material has been driven off
the amount of substance is measured in mole (n)
the number of particles in one mole is called Avogadro's number (NA) where NA=6.02*10^23 particles
the relationship between amount of substance (n), mass (m) and molar mass (M) is given by n=m/M
the relationship between volume (V), pressure (p), temperature (T) and amount gas in mol (n) is given by the general gas equation pV=nRT
at STP one mole of a gas occupies 22.4L and at SLC one mole of gas occupies 24.5L
the number of mole of a gas can be determined from the volume (V) and the molar volume (Vm) n=V/Vm
the empirical formula indicates the simplest whole number ratio of atoms present in a compound
empirical formulas can be determined by gravimetric analysis
the analysis of combustion products of an organic compound can be used to determine its empirical formula
a molecular formula gives the actual number of atoms of each element present in a molecule of the compound
the molecular formula can be determined from an empirical formula is the molar mass is known
the stiochiometry of a chemical reaction can be used to determine the amount of product formed or the amount of reactant consumed
the mass of precipitate formed in a precipitation reaction can be used to determine the purity or composition of some substances. The solid precipitate is heated to a constant mass to ensure that it is dry.
the composition of a mixture, the purity of a compound and empirical formula can be determined by gravimetric analysis
gravimetric analysis makes use of chemical ideas such as the mole concept, general gas equation and the degree of solubility of precipitates

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Chemistry 2 Heinmann 4th edition VCE units 3&4, 2014

Chapter 2 - analysis by mass