LAB 4 Density, Specific gravity, Specific volume, and Expressions of concentration 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 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) 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 54.96 mL of an oil weighs 52.78 g, what is the specific gravity of the oil ? Specific gravity of oil = 52.78 g/ 54.96 g = 0.9603 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 Specific Volume • Example: calculate the specific volume of a syrup, 91 mL of which weighs 107.16 g 107.16 g of water measures 107.16 mL specific volume = 91/107.16 = 0.849 Percentage • Percent % mean in a hundred • Percentage means rate per hundred Example 12.5% = 12.5 /100, or 0.125 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 Percentage • Example how many grams of dextrose are required to prepare 4000 mL of a 5% solution? 5g 100mL x 4000mL x = 5 x 4000 / 100 = 200g 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 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 Practice problems 1. 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? 2. How many grains of atropine sulfate should be used in compounding the following prescription? Rx Atropine sulfate 2% Distilled water q.s. Ad Ʒiv Sig. use in the eye 3. If 250 mL of alcohol weighs 203 g. what is the density? 4. If a liter of cough syrup weighs 1285 g, what is its specific gravity? Practice problems 5. The specific gravity of alcohol is 0.815. what is its specific volume? 6. 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? 7. How many grams of a drug substance should be dissolved in 240ml of water to make 4% w/w solution? 8. Five pints of diluted hydrochloric acid weighs 2.79 kg. calculate its specific gravity Practice problems 9. How many grams of potassium permanganate should be used in preparing 500 mL of 1:2500 solution? 10. How many milligram of hydrocortisone should be used in compounding the following prescription? Rx Hydrocortisone 1/8% hydrophilic ointment ad 10g Sig. apply BID 11. 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 12. Two 10 mL samples of urine have specific gravities 1.003 and 1.03. what is the difference in weight, in milligrams, between the two samples? Practice problems 13. What is the ratio strength w/v of a solution made by dissolving 2 tablets, each containing 0.125 g of mercury bichloride, in enough water to make 500 mL 14. How many mL of a 1:400 w/v stock solution should be used to make 4 liters of 1:2000 w/v solution? 15. How many grams of drug substance are required to make 120mL of 20% w/w solution having a specific gravity of 1.15 Home work 1. A piece of copper metal weighs 53.6 g and has a volume of 6 minims. Calculate its dinsety. 2. If 1000 mL of syrup with specific gravity of 1.313 contain 850 g of sucrose, what its percentage strength w/w? 3. If chloroform has a specific gravity of 1.476, what is its specific volume?