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lab 4

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 .

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lab 4

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  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 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

  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 • 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

  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? 5g 100mL x 4000mL 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 2% 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 0.815. 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 1/8% 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 1.003 and 1.03. 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 0.125 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 1.313 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?

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