Calculation of Normality
Equivalent weight (EW) = Molecular weight (MW) / Valency (Z)
Normality (N) =Equivalent weight (EW) / Volume of Solution (1000 ml.)
Meq = Actual weight (W) / Equivalent weight (EW)
Example: Molecular wt of K2Cr2O7 is 294.148 gm
Valency = 6 (because of Cr -6)
EW = 294.148/6 = 49.025
N = 49.025/1000 ml = 0.049025.
To make 0.25 N solution:
= 0.25 x EW = 0.25 x 49.025
= 12.256 gm. of K2Cr2O7 is required.
Molarity = Molecular Weight, gms / One Liter of Distilled Water
1 M NaCl = 58.5 gm NaCl in 1 Ltr of D.W. = 58500 mg/Ltr
0.5 M NaCl = 29250 mg/Ltr toxic for Bacteria