asofRules for solving ratio solution problems arefollows:W/W solution: Divide the total weight (grams)solution desired by the larger number of theratio, and the quotient will be the number ofgrams of the solute to be used.Example: How many grams of KMNO_{4 }areneeded to make 500 g of a 1:2000 solution?500+ 2000 = 0.25g of drug needed.500-0.25 = 499.75g of solvent needed.W/V solution: Divide the total volume in mlof solution desired by the larger number of theratio, and the quotient will be the number ofgrams of the solute needed.Example: How many grams of bichloride ofmercury are needed to prepare 500 ml of a 1:1000solution?5OO+1OOO=0.5g of drug needed.Take 0.5 g of the drug and add sufficient (q.s.with) solvent to make 500 ml; this gives you 1:1000strength.V/V Solution: Divide the total volume in mlof the solution desired by the larger number ofthe ratio, and the quotient will be the number ofml of the drug to be used.Example: How many milliliters of HCl wouldbe used to prepare a 1:250 solution with the totalvolume to be 500 ml?500+ 250= 2 ml of HCl neededof the stock solution and enough solvent (water)to make the total volume measure 60 ml.SPECIFIC GRAVITYSpecific gravity is the ratio of the weight ofa given substance to the weight of an equal volumeof a substance chosen as a standard. It is a meansof determining the strength, purity, or volume ofa substance. Water is the chosen substance as thestandard for solids and liquids.It is known that water has a unit weight of 1 gper ml of space occupied. Basic formulas predi-cated on this information are as follows:ml x S/G = weightweight= mlS /Gweight = S/GmlSample problems:1. What is the weight in grams of 300 ml ofalcohol with a specific gravity of 0.8?2. 900 g of glycerine with a S/G of 1.25 wouldmeasure how many milliliters?Percentage solutions from stock and/or ratiosolutions:Example: From a 1:10 solution of silver nitratein water, prepare 60 ml of a 1.5% solution of thesame ingredients.A 1:10 (W/V) solution contains 1 g of soluteand enough solvent (q.s.) to total a 10 ml solu-tion (finished product). Therefore, 1 ml of thesolution would contain 0.1 g of the solute. Sinceit is required that 0.9 g of the solute be used toprepare 60 ml of the required strength, use 9 ml3. If 50 ml of a liquid has a weight of 50.5 g,what is the specific gravity?COMPOUNDINGBy definition,compounding implies thevarious processes and procedures required tomanufacture a pharmaceutical preparation fordispensing to the patient. The art of compound-ing is a profession in itself, and a great deal more8-11

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