NTA Level 5 • Semester 2 • PST05208

Determination of Isotonicity by Molecular

Pharmaceutics Theory and Compounding • Source Session/Topic 14

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Session 14: Determination of Isotonicity by Molecular

Concentration Method

Total Session Time: 120 minutes + 6 hours of Practices

Prerequisites

• None

Learning Tasks

By the end of this session students are expected to be able to:

• Explain isotonicity by molecular concentration method

• Determine the isotonicity by molecular method

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board, chalk and whiteboard markers

• LCD projector and computer

SESSION OVERVIEW

Activity/

Step Time Content

Method

1 05 minutes Presentation Introduction, Learning Tasks

45 minutes Presentation Isotonicity by Molecular Method

Brainstorming

60minutes Presentation Determining the Isotonicity by Molecular

3 Concentration Method

Demonstration

4 05 minutes Presentation Key Points

5 05 minutes Presentation Evaluation

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SESSION CONTENTS

STEP1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing

STEP 2: Molecular Concentration Method (45 minutes)

• Molecular concentration: number unit i.e. molecules or ions or both presents in a solution

• A solution containing 1g molecule of a non – ionizing solute in 22.4 liters at normal temperature

and pressure (NTP) has an atmospheric pressure of one atmosphere

• Therefore a solution containing on gram molecule in 1 litre (a mole solution) will have osmotic

pressure of 22.4 atmosphere

• The molarity or molar concentration of a solute is defined as the number of moles of solute per

liter of solution (not per liter of solvent!):

• M=N/L Where M=molarity, N = number of mole and L = 1 litre of a solution

• N =M/MW where M = mass or weight and MW = molecular weight of compound

STEP 3: Determining the Isotonicity by Molecular Concentration Method (60

minutes)

Activity: Small Group Discussion ( 30 minutes)

DIVIDE students in small manageable groups

ASK students to discuss in groups on the following questions

• Calculate MW of compound x which contains 9.06g isotonic solution given dissociation

factor is 1.8.

REFER Students to Pharmaceutical Calculation. 13th Edition by HOWARD C.

ANSEL: Chapter 11, for reference

ALLOW students to discuss for 20 minutes

ALLOW each groups to present for 5 minutes

CLARIFY and SUMMARIZE by using the contents below

105

From freezing point = 1.86Ni

Where N = Number of mole and i dissociation factor

N = m/ mw and i = (% x p) + (100% – %) where p = number of ions after dissociation

Now

0.52 = 1.86 x N x 1.8

N = 0.52/ 1.86 x 1.8

N = 0.1553166

But N = M/MW

MW = m/N therefore 9.06g/0.1553166

Mw =58.33

STEP 4: Key Point (5 minutes)

• Molecular concentration is the number of units i.e. molecules or ions or both present in a solution

• A solution containing 1g molecule of a non – ionizing solute in 22.4 liters at normal temperature

and pressure (NTP) has an atmospheric pressure of one atmosphere

• Therefore a solution containing one gram molecule in 1 litre (a mole solution) will have osmotic

pressure of 22.4 atmosphere

STEP 5: Evaluations (5 minutes)

• What is molecular concentration

STEP 6: Take Home Assignment (5 minutes)

Activity: Take home Assignment (15 minutes)

ASK each individual student to do the following assignment

• Compound x contains 9.07g dissociate by 80% into two ions. Calculate molecular

weight of isotonic solution

ALLOCATE time for students to do the assignment and submit

REFER students to recommended references

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References

Ansel, H. C & Stocklosa, M. J. (2001). Pharmaceutical Calculations (11th ed.). Philadelphia, United

States: LIPPINCOTT WILLIAMS & WILKINS

Ansel, H. C (2010) Pharmaceutical Calculations (13rd ed.). Philadelphia, United States:

LIPPINCOTT WILLIAMS & WILKINS

Senya, S. S, Mwasha, C.Y, Muyinga, A. M, Amiri,R. I. and Mauga E.A.S.K. (2011) Tanzania

Pharmaceutical Handbook (2nd ed.). Dar eS Salaam, Tanzania: School of Pharmaceutical

Sciences.

Zatz, J.L and Teixeira, M.G. (2005). Pharmaceutical Calculation (4th ed.). New Jersey: John Wiley

& Sons,

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