Page 17 - Pharmaceutical_Analytical_Chemistry_1_Theoretical_Notes_Level_1

Mansoura National University
Pharm D-Clinical Pharmacy Program Level 1 Pharm. Anal. Chem. 1 (PC 101)

Example

How many grams of silver nitrate AgNO3 are needed to prepare 500 mL 0.3 M AgNO
3
solution? (Formula mass of AgNO = 170 g)
3

• No of liters (V) = mL of solution/1000 V= 500 mL
= 500/1000 = 0.5 liter Molarity= 0.3 M
• Molarity = No of moles of solute/No of liters of solution Molecular wt. = 170 g
0.3 = No of moles /0.5 Weight (g)??

• No of moles =0.3 X 0.5= 0.15 mol
• No of moles = Weight of solute (g) / Molecular wt. of solute

0.15= Weight (g) / 170
Weight = 0.15 X 170 = 25.5 g

Dilution and Molarity

▪ The molarity of a solution and its volume are inversely proportional.

▪ Therefore, adding water makes the
solution less concentrated.
▪ This inverse relationship takes the

form of:

× = ×

▪ So, as water is added, increasing the
final volume, V , the final molarity,
f
M , decreases.
f

Example : What is the volume of 6.0 M HCl that can be made from 5.0 mL of 12.0 M HCl?

× = × M = 12.0 M

i
12.0 × 5.0 = 6.0 × V V = 5.0 mL

f i
V = × = 10 mL M = 6.0 M
f f
12 V ???
f