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Solution of questions of the mid term exam Q:4// How many milliliters of 17% w/v of NaCl should be used in preparing 300 ml of a stock solution such that 15 ml diluted to 1 liter will yield a 1:5000 solution ? (20 mark) Solution : 1 liter = 1000 ml 1:5000 =1 g of NaCl in 5000 ml 1/5000 = x / 1000 X=0.2 g of NaCl in 1 liter (1000 ml) and it the same amount in 15 ml of stock solution before dilution 0.2g /15 ml = X/ 300 ml X = 4 g of NaCl needed in 300 ml stock solution Because we have 17% concentrate contains 17 g in each 100ml , so: 17g /100ml = 4g / X X = 23 ml of 17% w/v of NaCl stock solution needed. Q:5// A drug is commercially available in capsules each containing 12.5 mg of drug and 37.5 mg diluent . How many milligrams of additional diluent must be added to the contents of one capsule to make a dilution containing 0.5 mg of drug in each 100 mg of powder ? (15 mark) Solution : 12.5mg + 37.5 = 50 mg total weight of each capsule before dilution 12.5mg / 50mg = X / 100% X = 25% of drug in each capsule 0.5mg in 100 mg = 0.5% of drug in each capsule after dilution C1 Q1 = C2 Q2 25% 50 mg = 0.5% X X = 2500 mg the total weight of powder after dilution Because we have already 50mg of powder before dilution So: 2500 – 50 = 2450mg of diluent should be added Or 0.5 mg / 100 = 12.5 mg / X X = 2500 mg total weight then 2500 – 50 = 2450 mg of diluent should be added. Q:6// A manufacturing pharmacist has four lots of ointment containing 50%, 25%, 10% and 5% of medication . How many grams of each may be used to prepare 4800 g of a 20% ointment? Solution 50…………….10 parts of 50% ointment 25…………….15 parts of 25% ointment 20 10……………..30 parts of 10% ointment 5………………5 parts of 5% ointment -------60 total parts So: 10 p / 60p = X / 4800g X = (4800 10) / 60 X = 800g of 50% ointment must be used 15 p / 60p = X /4800g X = 1200g of 25% ointment used 30 p / 60p = X /4800g X = 2400g of 10% ointment used 5 p / 60p = X /4800g X = 400g of 5% ointment used (Checking : 800 + 1200 + 2400 + 400 = 4800) Or another Solution 50…………….15 parts of 50% ointment 25…………….10 parts of 25% ointment 20 10……………..5 parts of 10% ointment 5………………30 parts of 5% ointment -------60 total parts 15 p / 60p = X /4800g X = 1200g of 50% ointment used 10 p / 60p = X /4800g X = 800g of 25% ointment used 5 p / 60p = X /4800g X = 400g of 10% ointment used 30 p / 60p = X /4800g X = 2400g of 5% ointment used Solution of questions of the mid term exam Q:4// How many milliliters of 17% w/v of NaCl should be used in preparing 300 ml of a stock solution such that 15 ml diluted to 1 liter will yield a 1:5000 solution ? (20 mark) Solution : 1 liter = 1000 ml 1:5000 =1 g of NaCl in 5000 ml 1/5000 = x / 1000 X=0.2 g of NaCl in 1 liter (1000 ml) and it the same amount in 15 ml of stock solution before dilution 0.2g /15 ml = X/ 300 ml X = 4 g of NaCl needed in 300 ml stock solution Because we have 17% concentrate contains 17 g in each 100ml , so: 17g /100ml = 4g / X X = 23 ml of 17% w/v of NaCl stock solution needed. Q:5// A drug is commercially available in capsules each containing 12.5 mg of drug and 37.5 mg diluent . How many milligrams of additional diluent must be added to the contents of one capsule to make a dilution containing 0.5 mg of drug in each 100 mg of powder ? (15 mark) Solution : 12.5mg + 37.5 = 50 mg total weight of each capsule before dilution 12.5mg / 50mg = X / 100% X = 25% of drug in each capsule 0.5mg in 100 mg = 0.5% of drug in each capsule after dilution C1 Q1 = C2 Q2 25% 50 mg = 0.5% X X = 2500 mg the total weight of powder after dilution Because we have already 50mg of powder before dilution So: 2500 – 50 = 2450mg of diluent should be added Or 0.5 mg / 100 = 12.5 mg / X X = 2500 mg total weight then 2500 – 50 = 2450 mg of diluent should be added. Q:6// A manufacturing pharmacist has four lots of ointment containing 50%, 25%, 10% and 5% of medication . How many grams of each may be used to prepare 4800 g of a 20% ointment? Solution 50…………….10 parts of 50% ointment 25…………….15 parts of 25% ointment 20 10……………..30 parts of 10% ointment 5………………5 parts of 5% ointment -------61 total parts So: 10 p / 60p = X / 4800g X = (4800 10) / 60 X = 800g of 50% ointment must be used 15 p / 60p = X /4800g X = 1200g of 25% ointment used 30 p / 60p = X /4800g X = 2400g of 10% ointment used 5 p / 60p = X /4800g X = 400g of 5% ointment used (Checking : 800 + 1200 + 2400 + 400 = 4800) Or another Solution 50…………….15 parts of 50% ointment 25…………….10 parts of 25% ointment 20 10……………..5 parts of 10% ointment 5………………30 parts of 5% ointment -------- 61 total parts 15 p / 60p = X /4800g X = 1200g of 50% ointment used 10 p / 60p = X /4800g X = 800g of 25% ointment used 5 p / 60p = X /4800g X = 400g of 10% ointment used 30 p / 60p = X /4800g X = 2400g of 5% ointment used