the methods for expressing concentration and convertion of one unit to another is so important because not a single experiment is possible without measuring substance is an important factor in modern chemistry. Measuring substances by units is actually quantative analysis.
there are some methods to express the concentration.
Molar solution /Molarity
the amount of substance in mole present in one litter of any solvent at a certain temperature is known as Molar solution.
if there is 98 gm of sulphuric acid is dissolved in one litter of solvent then the solution is termed as one molar solution of sulphuric acid.
Here a term to highlight is the temperature dependence, why molar solution is depend on temperature?
molarity is actually substance present in one litter of solvent as voume of any solvent can change with temperature.
Molal solution/Molality
if there is one gm molecule of any substance is dissolved in 1000 gm solvent then the solution is termed as molal solution.
it is defined as small 'm '
indeed the total amount of substance dissolved in gm of solvent is known as molal solution for example if there is gm NaOH is dissolved ina solution the n the solution is ,molal or m
In actual practice molality is not used because there is two important factor on the solvent.
1. the density of the solvent
2. there may be a change in the volume after dissolving the solute.
it may be occured that the volume of gm solvent to increase or decrease from the actual volume ; but molality is free from temperature effect.
Normal solution/Normality
if one gm equivalent of a solute is dissolved in 1000 ml of a solvent then the solution is known as 1normal solution.
So for preparing 1 N Solution we need 1 equivalent of any substance dissolved in 1000 ml of any solvent.
Moreover equivalent weight is the part of any substance added with 1 part weight of Hydrogen or 8part weight of oxygen.
Capital "N" is the formal expression of normality. 5N means the solution containing 5 normal solute in 1000 ml solvent .
Formal solution/Formality
Some compounds like NaCl (electrolytic) dissolved in solved such a way that mola is not appropriate there
,for accounting this descripancy formality is used.
In any solution if there is solute present in gm-molecule per litter then the solution is known as formality.
Is expressed as "F"
The molecular weigh of KNO3 is 101.1 gm, if there is 101.1 gm KNO3 is present in 1 litter solution then the solution is 1 formal.
Gm/L
The amount of substance present in 1 litter is known as gm/L.
5gm/L of HCl means 5 gm of HCl is present in 1 litter.
Mole fraction
The ratio of mole of a substance to mole of total substance present in any solution is the mole fraction of the substance.
Mole fraction = mole of a specific substance/ total mole of substance.
It is just a ratio as a result it does not depend on the temperature. Nowadays it is not used in laboratory experiments. It has only some calculational value.
PPM
Parts per million or ppm is defined as that the amount of substance in Weight that present in one million either weight or volume.
It is used in micro anlytical system, a very small quantity of substance is present in concentration. Its a environment friendly system. If there is solvent M and solute m then in
PPM = m/M ×1000000
PPB
PPB or perts per billion is defined as that the amount of solute in microgram present in one litter of any solvent. It may be either weight or volume.
If m gm solute is present in M litter of any solvent then PPB can be expressed as
PPB =m/M×1000000000.
W/V
Its a system where solute is expressed in weight and solvent in which the solute is dissolved is in volume.
The meaning of 4%W/V aqueous solution of NaCl is 4 gm NaCl is dissolved in 100 ml of water.
W/W
The solute and solvent both is expressed in weight.
2% H2SO4 W/W meaning 2 gm sulphuric acid is dissolved in 100 gm solvent.
I.e the amount of substance present in 100 gm of solvent is w/w expressiomore
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