Summary

Summary - Pharmacy (MPIT011)

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Module
Pharmacy (MPIT011)

Institution
University Of The Witwatersrand (wits)

Pharmacy calculations notes are essential study materials for pharmacists, ensuring they have the knowledge and skills to safely and accurately dispense medications to patients. These notes provide a structured approach to solving complex dosage and medication preparation problems encountered in da...

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Uploaded on April 5, 2024
Number of pages 5
Written in 2021/2022
Type Summary

notes

Institution
University of the Witwatersrand (wits)
Module
Pharmacy (MPIT011)

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BPharm 1 2021
Pharmaceutical Calculations
MPIT011
Ratio and Dilution/concentration

You need to revise the following to be able to do these calculations:
 Increasing and decreasing of formulae
 The meaning of solute, solvent and solution
 Calculation of the number of moles
mass m
eg no of mol = or n =
relative molecular mass RMM
 The meaning of density where density is mass/unit volume or
the mass in grams of 1 millilitre of the substance
m
ie ρ =
v
 Concentrations eg a) mol/1000ml or mol/dm 3 b) % m/v c) % v/v d) % m/m
-----------------------------------------------------------------------------------------------------
Concentration is sometimes expressed as parts of a component in a product
Eg NaCl (s)in a solution
NaCl = 1 in 50 means 1 part of NaCl (s) in 50 parts of the product
ie 1g of NaCl in 50ml of SOLUTION NaCl (aq)
or we can say a solution is diluted 1 part in 50
or 1 to 50

A solid associated with a solid

or the mass of the component in the mass of the product
eg 1 part in 10 of aspirin means 1g of aspirin in 10g of powder mass

A liquid associated with a liquid

or the volume of a liquid component in the volume of product
eg 1 part of ethanol in 20 parts of SOLUTION
or 1ml ethanol in 20 ml of solution

A gas associated with a liquid

eg 1 part CO 2 in 1000 parts H 2 O

Or 1g of CO 2 in a 1000g of H 2 O

Remember also concentration expressed as a % = the proportion of a specific item x 100
amount of item x 100 amount of solute x 100
eg % w/w = , %w/v = and
total amount amount of solution
volume of component x 100
%v/v =
volume of solution

Page 1 of 5

, Examples

1)How many grams of coal tar are there in 300g of coal tar and zinc ointment containing
10%w/w coal tar?

Using the formula for %
quantity of coal tar x 100
%w/w =
total quantity of ointment
quantity of coal tar = %w/w x total quantity of ointment
10 x 300g
=
100
= 30g coal tar

Using ratios
10%w/w coal tar ointment means
10g coal tar in 100g of ointment
x g coal tar in 300g of ointment
300 x 10
x = 30g coal tar
100

2a) How many milliliters of ethanol are there in a 400ml ethanol solution if the dilution is 1
in 32 of ethanol solution?
b) Express 1 in 32 ml of ethanol as a %v/v concentration
c) Describe how you would make up the 400ml ethanol solution in (a) practically

1 in 32 of ethanol means
1 ml of ethanol in 32 ml of ethanol solution
x ml of ethanol in 400 ml of solution
400ml x 1 ml
x = = 12,5 ml of ethanol
32ml

b) a 1 in 32 dilution means
1ml of ethanol in 32 ml of solution
x ml of ethanol in 100ml of solution
100 x 1
x = %v/v = 3,125 %v/v
32

c) To make this up practically, take 12,5ml of absolute ethanol (100%v/v ethanol) and add to
350ml of purified water. Allow to cool because the reaction is exothermic and the volume will
contract on cooling. When this has cooled make up to the 400ml mark in a measuring cylinder.

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