Danielle DelVillano PharmD Objectives Define density specific gravity and specific volume and determine each through appropriate calculations Apply specific gravity correctly in converting weight to volume and volume to weight ID: 495240
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Slide1
Pharmaceutical Calculations: Density, Specific Gravity, and Specific Volume
Danielle DelVillano, Pharm.D.Slide2
Objectives
Define density, specific gravity, and specific volume and determine each through appropriate calculations
Apply specific gravity correctly in converting weight to volume and volume to weightSlide3
Density
Mass per unit volume of a substance
Most often expressed as
g/mL
Density =
Mass
VolumeSlide4
Density Example
If 10
mL
of sulfuric acid weighs 18
g
, what is its density?
Density =
18
g
10
mL
= 1.8
g/mLSlide5
Specific Gravity
Ratio of a weight of substance to a weight of equal volume of standard
Usually water
Expressed without units
Specific Gravity =
Weight of substance
Weight of equal vol. waterSlide6
Specific Gravity Example
If 54.96
mL
of an oil weighs 52.78
g
, what is the specific gravity of that oil?
Specific Gravity =
52.78
g
oil
54.96
g
water
*why 54.96
g
of water? Because 54.96
mL
of water weighs 54.96
g
(specific gravity of 1)Slide7
Displacement (Plummet) Method
A body immersed in a liquid displaces an amount of the liquid equal to its own volume and suffers an apparent weight loss in weight equal to the weight of the displaced liquid
Weigh plummet in air
Weigh plummet in water
Weight plummet in oil
Weight of displaced oil = weight of plummet in air – weight of plummet in oil
Weight of displaced water = weight of plummet in air - weight of plummet in waterSlide8
Plummet Method Example
A glass plummet weighs 12.64
g
in air, 8.57
g
when immersed in water, and 9.12
g
when immersed in an oil. Calculate the specific gravity of the oil.
Specific gravity =
Weight of displaced oil
Weight of displaced water
=
12.64
g
– 9.12
g
12.64
g
– 8.57
g
= 0.865Slide9
Specific Volume
Ratio of the volume of a substance to an equal weight of another substance taken as a standard
Water Slide10
Specific Volume Example
If 25
g
of glycerin measures 20
mL
and the standard for comparison is (25
g
) water, what is the specific volume of glycerin?
Specific Volume =
20
mL
glycerin
25
mL
water
= 0.8Slide11
Practice ProblemsSlide12
Chapter 5 Page 73
What is the weight, in grams, of 3620
mL
of alcohol with a specific gravity of 0.820?Slide13
Chapter 5 Page 74
What is the volume, in pints, of 50 lbs of glycerin having a specific gravity of 1.25?Slide14
Chapter 5 Problem 2
A piece of copper metal weighs 53.6
g
and has a volume of 6
mL
. Calculate its density.Slide15
Chapter 5 Problem 6
If 380
g
of cottonseed oil measures 415
mL
, what is its specific gravity?Slide16
Chapter 5 Problem 15
If chloroform has a specific gravity of 1.476, what is its specific volume?Slide17
Chapter 5 Problem 18
What is the weight, in pounds, of 5 pints of nitric acid?Slide18
Chapter 5 Problem 27
If fifty glycerin suppositories are made from the following formula, how many milliliters of glycerin, having a specific gravity of 1.25, would be used in the preparation of 96 suppositories?
Glycerin 91
g
Sodium
stearate
9
g
Purified
water
5
gSlide19
Chapter 5 Problem 29
How many grams of dextrose are
contained
in a
250
mL
intravenous infusion of a dextrose injection containing 60
g
of dextrose per 100
mL
if its specific gravity is 1.20? Slide20
Chapter 5 Problem 24
Glycerin,
USP
(specific gravity 1.25) costs
$54.25 per pound. If students in a
dispensing
laboratory use 1 pint of glycerin in preparing compounded prescriptions, what is the cost of the glycerin used? Slide21
QuestionsSlide22
Reference
Ansel
, H. C. (2009)
Phamaceutical
Calculations
(13th Ed.).
Philadelphia:Lippincott
Williams & Wilkins, and
Wolters
Kluwer
Publishers