Analytical Chem istry - DePauw University

Chapter 2 Basic Tools of Analytical Chemistry192B.1 Molarity and FormalityBoth molarity and formality express concentration as moles of soluteper liter of solution. There is, however, a subtle difference between molarityand formality. Molarity is the concentration of a particular chemicalspecies. Formality, on the other hand, is a substance’s total concentrationwithout regard to its specific chemical form. There is no difference betweena compound’s molarity and formality if it dissolves without dissociatinginto ions. The formal concentration of a solution of glucose, for example,is the same as its molarity.For a compound that ionize in solution, such as NaCl, molarity andformality are different. Dissolving 0.1 moles of CaCl 2 in 1 L of water givesa solution containing 0.1 moles of Ca 2+ and 0.2 moles of Cl – . The molarityof NaCl, therefore, is zero since there is essentially no undissociated NaCl.The solution, instead, is 0.1 M in Ca 2+ and 0.2 M in Cl – . The formalityA solution that is 0.0259 M in glucose is0.0259 F in glucose as well.Table 2.4 Common Units for Reporting ConcentrationName Units Symbolmolaritymolessoluteliters solutionMformalitymolessoluteliters solutionFnormalityequivalentssoluteliters solutionNmolalitymolessolutekilogramssolventmweight percentgramssolute100 gramssolution% w/wAn alternative expression for weight percentisvolume percentweight-to-volume percentmL solute100 mL solutiongramssolute100 mL solution% v/v% w/vgramssolutegramssolution ×100You can use similar alternative expressionsfor volume percent and for weight-tovolumepercent.parts per millionparts per billiongramssolute610 gramssolutionppmgramssolute910 gramssolutionppb