1. Advantages and disadvantages of solutions
Easy to swallow, especially for pediatric and geriatric patients
Dissolved drug is immediately available for GI tract, thus onset of therapeutic response is fast.
Uniform distribution of the drug in the dosage form
Flexible dosing according to the weight and age of the patient
Immediate dilution in the GI tract fluids avoids irritation
Disadvantages:
Bulky, inconvenient for transport and storage and glass is breakable
Stability is poor due to hydrolysis
Active drug and excepients may chemically interact more readily in solution than in solid dosage form
Suitable medium for microbial growth
Unpleasant taste will be amplified when drug is in solution

2. Molarity(M): Moles of solute in 1000 ml of solution
A. Solid in liquid solubility e.g., NaCl or Sugar in water Concentration Expressions of Solutions
Molarity(M): Moles of solute in 1000 ml of solution
Molality* (m): Moles of solute in 1000 gm of solvent
Mole Fraction(A): Ratio of the moles of one constituent (solute or solvent) of a solution to the total moles of all constituents (solute and solvent).
Mole percent: is obtained by multiplying mole fraction by 100.
Number of Moles: Weight in grams divided by molecular weight in gm / mole
* Note that molality is the only concentration unit in which
denominator contains only solvent information rather than solution.

3. Other concentration expression: % Concentration
% (w/w) =
% (w/v) =
% (v/v) =

4. Example:
An aqueous solution of ferrous sulphate (FeSO4) was prepared by adding 41.5 gm of FeSO4 to enough water to make 1 L of solution at 18o C. The density of the solution is gm/mL, and the molecular weight of FeSO4 is gm/mol and molecular weight of H2O is gm/mol .
Calculate
A) the Molarity FeSO4;
Number of moles of FeSO4 = Weight ÷ molecular weight
Number of moles of FeSO4 = 41.5gm ÷ gm/mol = moles
Molarity (M) = No. of moles in liters of solution
Molarity = ÷ 1 L = M
B) the Molality FeSO4;
Molality = No. of moles in 1000 gm of solvent
No. of moles = moles
Volume of solution= 1000 ml, But weight of solvent is not known.
Weight = volume X density
Weight of solution = 1000 ml X gm/ml = gm
Weight of solvent = gm gm = 996 gm =0.996 kg
Molality = ÷ kg= m

5. Example-continued:
An aqueous solution of ferrous sulphate (FeSO4) was prepared by adding 41.5 gm of FeSO4 to enough water to make 1 L of solution at 18o C. The density of the solution is gm/mL, and the molecular weight of FeSO4 is gm/mol and molecular weight of H2O is gm/mol .
C) the mole fraction and mole percent of water.
Mole fraction (X1) of water = moles of water/ (moles of water moles of FeSO4)
Moles of water = 996 gm ÷ gm/mol = moles
Mole fraction (X1) of water = / ( )=
Mole percent of water = mole fraction X 100
Mole percent of water = X 100 = 99.51%
D) the mole fraction and mole percent of FeSO4;
Mole fraction (X2) of FeSO4 = moles of FeSO4 / (moles of water moles of FeSO4)
Mole fraction (X2) of FeSO4 = / ( ) =
mole percent of FeSO4 = mole fraction X 100
mole percent of FeSO4 = X 100 = 0.49%
N.B
Sum of X1 and X2 = = 1.00

6. Example-continued:
An aqueous solution of ferrous sulphate (FeSO4) was prepared by adding 41.5 gm of FeSO4 to enough water to make 1 L of solution at 18o C. The density of the solution is gm/mL, and the molecular weight of FeSO4 is gm/mol and molecular weight of H2O is gm/mol .
E) the percent w/w of FeSO4.
the percent w/w of FeSO4 = (weight of FeSO4 ÷ weight of solution)X100
the percent w/w of FeSO4 = (41.5 gm ÷ )X100 = 4% w/w
F) the percent w/v of FeSO4.
the percent w/v of FeSO4 = (weight of FeSO4 ÷ volume of solution)X100
the percent w/v of FeSO4 = (41.5 gm ÷ 1000 ml)X100 = 4.15% w/v

7. Other descriptive terms of solubility:
Very soluble one gm of solute / one ml of solvent
Freely soluble one gm of solute/ from 1 to 10 mls of solvent
soluble one gm of solute/ from <10 to 30 mls of solvent
sparingly soluble one gm of solute/ form < 30 to 100 mls of solvent
slightly soluble one gm of solute/ form < 100 to 1000 mls of solvent
very slightly soluble one gm of solute/ form < 1000 to mls of solvent
practicaly insoluble or insoluble one gm of solute/ more than 10,000 mls of solvent