Expressions
of solution concentrations:
|
mole |
molecular weight of a substance in grams
[gm molecular
weight] Number of atoms in 12 gm of carbon 12 6.02 x 1023 atoms,
ions, molecules [Avogadros number] |
|
molar [molarity] |
weight per volume concentration ie 1 molar solution contains 1 mole of
the specified solute per 1000 mls solution eg 180 gm dextrose made up to 1 L 1
molar concentration of dextrose eg 58.5 gm NaCl [ Na=23 + Cl=35.5] in 1 L
solution 1 molar concentration |
|
molal [molality] |
a weight per weight designation ie 1 molal solution contains 1 mole of
the specified solute per 1000 gms solution less used in medicine |
|
equivalents |
gram-equivalent weight of a substance is
that weight of a substance that will react with 1 mole [1.008 gm] H+ eg 1 mole (58.5 gm) NaCl in 1 L solution
[ie a 1 molar concentration]; as have 1 mole Na + 1 mole Cl and both Na &
Cl have valencies of 1, the Na in this 1 molar solution is equivalent to 1
mole of hydrogen & ditto for Cl the concentration of Na+ (& Cl-) is one
equivalent per litre eg 1 mole (111 gm) CaCl2 in 1 L
solution [ie a 1 molar concentration]; as have 1 mole Ca + 2 mole Cl and as
Ca has a valency of 2 & Cl a valency of 1, the Ca in this 1 molar
solution is equivalent to 2 mole of hydrogen & ditto for Cl the
concentration of Ca2+ (& Cl-) is two
equivalents per litre |
|
normality |
a normal
solution has 1 gm equivalent weight [1 mole] of solute in 1 L of solution another means of expressing equivalents not used in medicine |
1 Molar
solution NaCl
58.5 gm NaCl [ Na=23 + Cl=35.5] in 1 L
solution 1 molar concentration
0.25 Molar
solution NaCl
58.5/4 gm NaCl =
14.625 gm in 1 L solution 1/4 molar concentration
note 0.9% Normal saline =
0.9 gm NaCl in 100 ml water
= 9 gm NaCl in 1000 ml
water
= 58.5 gm : 1 mole
9 gm : x mole x
= 9/58.5 =
= 0.154 moles NaCl in 1L solution
= 154 mmolar solution