Molar Concentration / Molarity of Solutions

Molar Concentration 

is able to compare the amount of solute dissolved in a certain volume of solution.

**Need to know formula**

Molar concentration = Moles of solute (n)   /   Volume of solution (V in liter)

moles of solute= molarity X volume of solution 
Volume of solution= moles of solute/molarity

 

is the number of moles of solute in one litre of a solution. We use "M" to denote molar concentration and it has the units of "moles/L".

solute: smaller quantity being dissolved

solvent: larger quantity being dissolved 

**Example of Molarity ConcentratioN **

• EXAMPLE 1
  
  EXAMPLE 2
  If 20g of NaOH is dissolved in sufficient water to produce 500 mL of solution, calculate the molar concentration in molarity.
  
  
   Molecular mass of NaOH                =  40g /mole
  20 g of NaOH                                   =  20g / 40g /mole   = 0.5 mole
  (g and g units cancel each other. mole is transposed to the numerator)
  500 mL of solution contains            = 0.5 mole
  1000 mL   contains                           = 0.5 mol  x  1000 mL / 500 mL = 1 mol
  By definition, the molar concentration is 1 mol /1000 L = 1M 
  
  
  EXAMPLE 3
  Given that conc. HCL has a density of 1.18 and has about 35% HCL dissolved what is its molar concentration (molarity) ?
  
  
  Take 100 mL of HCL. Use the density information to convert volume into mass. Its weight is given by 100mL x 1.18 g/mL = 118 g
  Amount of HCL = 118 g x 35% =  41.3g 
  Molecular mass of HCL is 36.5 g/ mole
  41.3 g = 41.3g/36.5 g/mole = 1.13 moles
  100 mL of solution contains 1.13 moles
  1000 mL contains 1.13 mole x 1000 mL /100 mL = 11.3 moles / liter = 11.3 M
  
  
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