Concentration
Quantity of solute that is dissolved in known quantity of solvent is a concentration of solution.
Knowing the quantity of solute present in solution is very important.
So that determining the concentration of solution also important.
The concentration of solution expressed both qualitatively and quantitatively.
Qualitative Representation:
Dilute Solution:
Dilute solution means smaller proportion of solute present in solution, as compare to proportion of solvent.
Concentrated solution:
Concentrated solution means, more proportion of solute present in solution, as compare to proportion of solvent.
Example:
A : 2 gram NaCl dissolved in 100 ml water.
B: 20 gram NaCl dissolved in 100 ml water.
Soln. A is comparatively dilute than soln. B.
OR
Soln. B is comparatively concentrated than Soln. A.
Quantitative Representation:
To quantitative representation of concentration following terms are using.
A] Mass Percentage:
Mass percentage is also called weight percentage.
The amount of solute in grams dissolved in 100gm of water.
If 5 gm NaCl (Solute) dissolved in 100gm water, then mass percentage of NaCl is,
Mass percent of NaCl = Mass of NaCl / Mass of solution X 100
= 5/(5+20) X 100
=5/25 X 100 =20% w/w.
B] Volume Percentage:
In some case if solute is liquid then solute can take in ml and dissolved in solvent make the final volume of solution upto 100 ml.
If 20 ml acetone dissolved in water upto volume of solution is 100 ml, then volume percentage of acetone is,
Volume percentage of Acetone = Volume of Acetone / Volume of solution X 100
= 20 ml/100ml X 100 = 20% v/v
C] Mass by volume percentage :
It means known quantity of solute ( in grams ) dissolved in solvent make the final volume of solution upto 100 ml.
If 20 gm NaCl dissolved in water and make the final volume of solution upto 100 ml then mass by volume percentage of NaCl is,
Mass by volume percentage of NaCl = Mass of solute in grams / Volume of solution in ml X100
= 20(gm ) /100 (ml) X 100
= 20 % gm/ml OR 20% w/v.
D] Molarity :
Most common unit of concentration is molarity.
It is denoted by M.
Molarity means no, of moles present in exactly 1 lit. solution.
Molarity = No. of moles of solute / Volume of solution in Lit.
Unit of molarity = mol/lit.
1.6 Molar solution of Butyl lithium in hexane means 1.6 moles of butyl lithium present in 1.0Lit. solution.
E] Molality :
Molality means no. of moles of solute dissolved in 1 Kg of solvent.
Denoted by m.
Molality = No. of moles of solute / Mass of solvent in Kg.
