1. lab 4
Density, Specific gravity, Specific volume, and Expressions of concentration

2. Density Density is mass per unit volume of a substance.
Example if 10 ml sulfuric acid weighs 18g, its density is? Density = 18(g)/ 10(mL) = 1.8 g/mL

3. Specific Gravity
Specific gravity: is a ratio, weight of substance / weight of equal volume of standard substance have the same temperature.
For specific gravity of liquid and solids, water used as standard.
10 mL of H2O = 10 g (weight)

4. Specific Gravity
Substance that have specific gravity less than 1 are lighter than water
Substance that have specific gravity greater than 1 are heavier than water
Example if mL of an oil weighs g, what is the specific gravity of the oil ? Specific gravity of oil = g/ g =

5. Specific Gravity
The following equation may be used to convert the volume of substance or pharmaceutical preparation to its weight:
g = mL x sp gr
The following equation may be used to convert the weight of substance or pharmaceutical preparation to its volume: mL = g sp gr

6. Specific Volume specific volume = 91/107.16 = 0.849
Example: calculate the specific volume of a syrup, 91 mL of which weighs g g of water measures mL
specific volume = 91/ = 0.849

7. Percentage Percent % mean in a hundred
Percentage means rate per hundred
Example 12.5% = 12.5 /100, or 0.125

8. Percentage
Percent weight-in-volume (w/v): the number of grams of a constituent in 100 mL of solution or liquid preparation
Percent weight-in-weight (w/w): the number of grams of a constituent in 100 g of solution or preparation.
Percent volume-in-volume (v/v): the number of milliliters of a constituent in 100 mL of solution or liquid preparation

9. Percentage
Example how many grams of dextrose are required to prepare 4000 mL of a 5% solution? g mL x mL x = 5 x 4000 / 100 = 200g

10. Percentage
Example: 5 g of glycerin in 100 mL syrup, express it as % v/v. (sp gr 1.25) 5 g/ 1.25 = 4 ml 4 % v/v

11. Ratio Strength
Ratio strength is another way of expressing percentage strenght. Example: 1% w/v solution is equivalent to 1:100 w/v ratio strength
The concentrations of very weak pharmaceutical preparations (usually weight-in-volume) often are expressed in terms of their ratio strengths. Example: 1: 10,000 w/v means 1 gram of solute in 10,000 mL of solution

12. Practice problems
In preparing 250 mL of a certain lotion, a pharmacist used 4 mL of liquefied phenol. What was the percentage (v/v) of liquefied phenol in the lotion?
How many grains of atropine sulfate should be used in compounding the following prescription? Rx Atropine sulfate % Distilled water q.s. Ad Ʒiv Sig. use in the eye
If 250 mL of alcohol weighs 203 g. what is the density?
If a liter of cough syrup weighs 1285 g, what is its specific gravity?

13. Practice problems
The specific gravity of alcohol is what is its specific volume?
If 100 mL of pharmaceutical preparation contains 20 µL of 50% w/v solution of Benzalkonium chloride, what is the percentage strength of that agent in the solution?
How many grams of a drug substance should be dissolved in 240ml of water to make 4% w/w solution?
Five pints of diluted hydrochloric acid weighs 2.79 kg. calculate its specific gravity

14. Practice problems
How many grams of potassium permanganate should be used in preparing 500 mL of 1:2500 solution?
How many milligram of hydrocortisone should be used in compounding the following prescription? Rx Hydrocortisone /8% hydrophilic ointment ad 10g Sig. apply BID
A pharmacist incorporate 6 g of coal tar into 120 g of 5% coal tar ointment. Calculate the percentage w/w of coal tar in the finished product
Two 10 mL samples of urine have specific gravities and what is the difference in weight, in milligrams, between the two samples?

15. Practice problems
What is the ratio strength w/v of a solution made by dissolving 2 tablets, each containing g of mercury bichloride, in enough water to make 500 mL
How many mL of a 1:400 w/v stock solution should be used to make 4 liters of 1:2000 w/v solution?
How many grams of drug substance are required to make 120mL of 20% w/w solution having a specific gravity of 1.15

16. Home work
A piece of copper metal weighs 53.6 g and has a volume of 6 minims. Calculate its dinsety.
If 1000 mL of syrup with specific gravity of contain 850 g of sucrose, what its percentage strength w/w?
If chloroform has a specific gravity of 1.476, what is its specific volume?