Calculations of Density and Specific Gravity
Session 6: Calculations of Density and Specific Gravity
Total Session Time: 60 minutes
Prerequisites
Students Learning Tasks
By the end of this session students are expected to be able to:
Resources Needed:
SESSION OVERVIEW
|Step |Time |Activity/ |Content |
| | |Method | |
|1 |05 minutes |Presentation |Introduction, Learning Tasks |
|2 |15 minutes |Presentation |Definition of Density and Specific |
| | |Brainstorming |Gravity |
|3 | |Presentation | |
| |30 minutes |Small group |Calculations of Density and |
| | |discussion |Specific Gravity |
|4 |05 minutes |Presentation |Key Points |
|5 | | Presentation |Evaluation |
| |05 minutes | | |
CONTENTS
STEP 1: 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: Definitionsof Density and Specific Gravity (15 minutes)
o The density of a substance is its mass per unit volume at a specific
temperature and pressure
o The symbol most often used for density is ρ (the lower case Greek
letter), although the Latin letter D can also be used
o Mathematically, density is defined as mass divided by volume
[pic]
Where ρ is the density, m is the mass, and V is the volume.
o In the SI system, density is the number of gram per one milliliter
o Different materials usually have different densities
o The density of a material varies with temperature and pressure
o At 20ºC, 1 Ml of water weighs 1g, thus 100g of water occupies a volume
o This 1:1 relationship is considered to hold, for most general
pharmaceutical purposes, at the normal ambient temperatures
o However, this 1:1 relationship between weight and volume is not true
for other liquids, solids and semisolids
o To simplify comparisons of density across different systems of units,
it is sometimes replaced by the specific gravity
o Thus specific gravity is the weight of a given volume of a substance
compared with the weight of an equal volume of water both having the
same temperature
o Relative density less than one means that the substance floats in
water.
|Specific Gravity |Weight of a given volume of a|
| |Weight of equal volume of |
| |water |
STEP 3: Calculations of Density and Specific Gravity (30 minutes)
|Activity: Small Group Discussion ( 20 minutes) |
| |
|DIVIDE students into small manageable groups |
|ASK students to discuss on the following question |
| |
|What is the density of a solution weigh 250g and 248mL? |
|What is the specific gravity of 365mL of glycerol weigh 460g? |
|REFER Students to Tanzania Pharmaceutical Handbook pg 25-28 |
| |
|ALLOW students to discuss for 15 minutes |
| |
|ALLOW few groups to present and the rest to add points not mentioned |
| |
|CLARIFY and SUMMARIZE by using the contents below |
The following are the solutions for the above exercise:
[pic]
| |liquid |
| |Weight of equal volume of |
| |water |
STEP 3: Key Points (5 minutes)
concentration
temperature and pressure
with the weight of an equal volume of water both having the same
temperature
STEP 4: Evaluation (10 minutes )
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.
New Jersey: John Wiley & Sons, Inc
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