This document discusses various physicochemical principles relevant to pharmacy, including expressions of concentration, calculations, equivalent weight, tonicity, and buffers. It covers ratios, percentages, parts, molar and equivalent solutions, milliequivalents, adjusting tonicity, and buffer systems and applications. The document is intended as a guide for pharmacists and students to understand various concentration expressions and physicochemical concepts.

1. PHYSICOCHEMICAL PRINCIPLES
Dr. Basavaraj K. NanjwadeM. Pharm., Ph. D
Department of Pharmaceutics
Faculty of Pharmacy
Omer Al-Mukhtar University
Tobruk, Libya.
E-mail: nanjwadebk@gmail.com
2014/06/03 1
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.

2. CONTENTS
• Introduction to expressions of concentration
• Calculations involving expressions of concentration
• Equivalent weight
• Milli-equivalent
• Tonicity (osmosis, methods of adjusting)
• Buffers (systems, drugs as buffers and applications)
• References
2014/06/03 2
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.

3. Introduction to expressions of
concentration
• May different ways of expressing concentration are
used and pharmacists should be familiar with them
and how to convert one to another.
• Sometimes prescripts are written using a mixture of
different expressions of concentration, so the
pharmacist must be familiar with these and be able to
convert them so that a consistent method of
expressing concentration is used.
• Perhaps the simplest expressions of concentration are
as a fraction (for example1/4), and as a decimal
expression (for example 0.25).
2014/06/03 3
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.

4. Calculations involving in
expressions of concentration
1. Ratios and percentages
• Percentage weight in weight (w/w)
• Percentage weight in volume (w/v)
• Percentage volume in volume (v/v)
• Miscellaneous examples
2. Parts
• Concentrated waters
3. Molar and Equivalent solutions
• Molarity
• Molality
• Mole fraction
2014/06/03 4
Faculty of Pharmacy, Omer Al-Mukhtar
University, Tobruk, Libya.

5. 1. Ratios and percentages
• A ratio is the relative magnitude of two like quantities. Thus:
1:10= 1 part in 10 parts,
Which might be 1 g in 10 g or 1 mL in 10 mL.
Therefore, if 1 g of sucrose is in 10 g of solution, the ratio is 1:10.
Equally, if we have 10 g of sucrose in 100 g of solution the ratio
remains 1:10.
A percentage is the number of parts per one hundred and is probably
the commonest expression of concentration used in pharmacy.
Returning to the example of sucrose above we can express 10 g
sucrose in 100 g of solution as 10%.
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
5

6. Percentage weight in weight
(w/w)
• A percentage weight in weight (% w/w) is the number
of grams of an active ingredient in 100 grams of a
mixture.
• It should be noted that the ingredients in this mixture
could be a solid or liquid , but for the latter, its
quantity would be measured by weight not volume.
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
6

7. Percentage weight in volume
(w/v)
• A percentage weight in volume (% w/v) is the
number of grams of an active ingredients in 100 mL
of liquid.
• Again the smaller quantity could be solid or liquid,
measured by weight, but the final mixture must be a
liquid since a volume is being measured.
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
7

8. Percentage volume in volume
(v/v)
• A percentage volume in volume (% v/v) indicates the
volume of an active ingredient in 100 mL of a liquid.
• In this case both ingredients must be liquids since
both are to be measured by volume.
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
8

9. Miscellaneous examples
• Sometimes a percentage is specified but no indication
given as to whether it is weight in weight, weight in
volume or volume in volume.
• In most situations it is assumed that solids in liquids
are percentage weight in volume and liquid in liquids
are percentage volume in volume.
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
9

10. 2. Parts
• When active ingredients are included in equal
amounts, or simple ratios, rather than using
percentages the prescriber may indicate the quantities
in parts.
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
10

11. Concentrated waters
• Liquid preparations for oral use are often flavoured to
make them more palatable for the patient.
• In extemporaneously prepared products the flavouring is
frequently a flavoured water, e.g. peppermint water, anise
water.
• These flavoured waters are available in a concentrated
form and are either used as such, or are diluted to provide
the vehicle for the preparation.
• All concentrated waters have the same dilution factor, i.e.
1part of concentrated plus 39 parts of water to give 40
parts of flavoured water.
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
11

12. 3. Molar and Equivalent
solutions
• Moles and equivalents are expressions of quantity.
Therefore, they can become part of an expression of a
concentration in a mixture.
• In pharmacy this is always in a volume, normally
expressed as mmol/mL, mmol/L, µmol/L or mEq/L.
• A 1 molar solution contains 1 mole of material
dissolved in 1 litre.
• Starting point it is possible to calculate the amount of
material required for different volumes of different
strengths of solution.
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
12

13. 2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
13
Molarity

14. 2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
14
Molarity

15. Molality
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
15

16. Normality
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
16

17. 2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
17
Mole fraction

18. 2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar
University, Tobruk, Libya.
18
Mole fraction

19. Milli-equivalent
(mEq)
• The concentrations of solutes in body fluids and in
solutions used as replacements for those fluids are
usually expressed in terms of the number of
millimoles (1 millimole = one thousandth of a mole)
in a litre of solutions.
2014/06/03 19
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
mEq =
molecular weight (expressed in milligrams)
Valence (equivalent weight)

20. Equivalent weight
• The weight of the substance which combines with 1
gram of hydrogen or 8 grams of oxygen is called as
equivalent weight.
• Equivalent weight is the weight of the substance
which loses or gains 1mole of electrons.
2014/06/03 20
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
Equivalent weight = molecular weight (expressed in milligrams)
valence (equivalent weight)

21. Formality
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
21

22. Tonicity
(Osmosis, Methods of adjusting)
• Tonicity: Tonicity are characteristics of parenteral
preparations. It is important that they be adjusted to
be as close as possible to the values for human blood,
to prevent damage to blood cells and organs.
• Osmosis: The osmotic pressure of a solution is the
external pressure that must be applied to the solution
in order to prevent it being diluted by the entry of
solvent via a process known as osmosis.
2014/06/03 22
Faculty of Pharmacy, Omer Al-Mukhtar
University, Tobruk, Libya.

23. Tonicity
(methods of adjusting)
1. Freezing point depression: The freezing point
depression of blood plasma and tears is 0.52 0
C. Thus
solutions that freeze at 0.52 0
C have the same osmotic
pressure as body fluids. Hypotonic solutions have a
smaller freezing point depression and require the
addition of a solute to depress the freezing point to 0.52
0
C
2. Some methods of calculating for isotonicity
• Sodium chloride equivalents
• Molar concentrations
• Serum osmolarity
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
23

24. Making solutions isotonic
• An isotonic solution is a solution in which body cells
can be bathed without a net flow of water across a
semipermeable membrane
– 0.9% normal saline (NS)
• Injection solutions are often made isotonic with 0.9%
w/v sodium chloride solution.
• The amount of solute, or the required dilution
necessary to make a solution isotonic, can be
determined by a number of different methods.
2014/06/03
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
24

25. Buffers
(systems, drugs as buffers and applications)
• Buffer are materials which, when dissolved in a solvent, will
enable the solution to resist any change in pH should an acid
or an alkali be added.
• The choice of suitable buffer depends on the pH and buffering
capacity required.
• It must be compatible with other excipients and have a low
toxicity.
• Most pharmaceutically acceptable buffering systems are based
on carbonates, citrates, gluconates, lactates, phosphates or
tartrates.
• Borates can be used for external application, but not to mucous
membranes or to abraded skin.
2014/06/03 25
Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.

26. THANK YOUe-mail: nanjwadebk@gmail.com
2014/06/03 26
Faculty of Pharmacy, Omer Al-Mukhtar
University, Tobruk, Libya.