4- CONCENTRATIONS: just a way to quantify the constituents of a solution.


Concentration of the different solutes of a solution can be expressed in:

g/L: weight of solute / liter of solution

%: Percentage concentration

mole/L of solution or M: Molarity - it is the # molecules of EACH solute found in a solution per unit of volume of solution. It is expressed in mole/ liter of solution

mole/kg of solvent or m: Molality - it is the # molecules of EACH solute found in a solution per unit of weight of solvent. It is expressed in mole / 1000g of solvent

Concentration of all the particles dissolved in the solution can be expressed in:

Osmoles/L of solution or Osm/L: Osmolarity - Total concentration of all osmotically active solute particles in the solution -
# of mole of solutes particles / liter of solution - (Saying that a solution has an osmolarity of 1 Osmol/L is equivalent to saying that it has a total of 1 mole of osmotically active particles, NO MATTER WHAT ARE THESE PARTICLES.)

Osmoles/kg of solvent: Osmolality - # of mole of all the solutes particles / kg of solvent

It is the TOTAL NUMBER of particles in solution that interest us here - we DO NOT CARE what they are (na+, glucose, Ca++, Cl- or urea): we want to count them all regardless of their species)

The concentration of substances that can provide (or accept) reactive agents is also expressed in equivalent/liter of solution (or less frequently in equivalent/kg of solvent).

These substances and their reactive agents are:
- acids and H+ (1 Eq/liter of solution of acid can provide 1 mole of H+ in titration)
- bases and OH- (1 Eq/liter of solution of base can provide 1 mole of OH- in titration)
- oxidizing substances and electrons (1 Eq/liter of solution of oxidizing substances can accept 1 mole of electron in a redox reaction)
- reducing substances and electrons (1 Eq/liter of solution of reducing substance can provide 1 mole of electron in a redox reaction)
- cations and positive electrical charges (1 Eq/liter of solution of cation provide 1 mole of positive charges)
- anions and negative electrical charges (1 Eq/liter of solution of acid provide 1 mole of negative charges)

In physiological solutions, we deal mainly with acid/base and cation/anion. Thus in this tutorial, we will focus on these and neglect oxidizing and reducing substances.

Concentration of Acid (or Base) is expressed in Eq/L and is called Normality N

Concentration of positive (or negative) charges in a solution are expressed in:

Eq/L of solution: Electrical Equivalent/L of solution
Eq/kg of solvent: Electrical Equivalent/kg of solvent