Calculations Workshop 1 Worked Answers

Calculations Workshop 1 Moles & Concentrations 1) How many moles of solute are there in 20ml of a 1 molar solution? 1molar=1mole in 1000ml 1ml 1/1000mole 20ml 1/1000 x 20 mole 0.02mole 0.02 mole 2) What is the molecular weight of aspirin? (C9H8O4). (Atomic weights C=12, H=1, O=16). C H O 9 x12 =108+ 8 x 1 =8+ 4 x 16 =64 180 180 3) You are required to prepare 150ml solution of MgCl (molecular weight 203.3) containing 4mmol/10ml of magnesium. What weight of MgCl is needed to make the solution? 4mmol in 10ml 60mmol(0.06mole) in 150ml Mass=mol x mol wt =0.06 x 203.3 =12.198g 12.198g 4) How many milligrams of sodium ions are contained in a 600mg tablet of sodium chloride? (Atomic weights Na = 23 Cl 35.5) Na = 23/58.5 In 600mg tablet 235.9mg 23/58.5 x 600= 235.9mg 5 Calculations Workshop 1 5) How much sodium fluoride will be required to make 250ml of a mouthwash containing 0.012mol/L of sodium fluoride? (molecular weight of sodium fluoride = 42) 0.012mol in 1000ml(1L) In 250ml (0.012/1000) x 250 = 0.003mol Mass=mol x mol weight =0.003 x 42 =0.126g 0.126g 6) How much sodium chloride is contained in 200ml of 0.9% sodium chloride intravenous solution? 0.9g in 100ml In 200ml (0.9/100) x 200 = 1.8g 1.8g 7) How many grams of sodium chloride are there in a 500ml infusion of sodium chloride 0.9%? 0.9g in 100ml In 500ml = 0.9 x 5 = 4.5g 4.5g 8) How much dithranol is required to make the following prescription? 1.5% w/w dithranol in Yellow soft parafÏn. Supply 450g. Apply as directed. 1.5g in 100g In 450g = 1.5 x (450/100) = 6.75g 6.75g 5 Calculations Workshop 1 9) Calculate how much zinc oxide is needed to make up 120g of the following ointment. Zinc oxide 7.5% w/w Castor Oil 50% w/w Arachis oil 30.5% w/w White beeswax 10% w/w Cetostearyl alcohol 2% w/w 7.5g in 100g In 120g = (7.5 x120) / 100 = 9g which is equiv to 9000mg 9000mg 10) You receive a prescription for 450g of 0.5% w/w menthol in aqueous cream. How much menthol is required to make up this cream? 0.5g in 100g In 450g = (0.5 x 450)/100 = 2.25g 2.25g 11) How many aspirin 300mg tablets does a patient dissolve in 120mls water to make up a 0.75% w/v aspirin solution? 0.75g in 100ml In 120ml = (0.75 x 120)/100 = 0.9g which is equiv to 900mg = 3 x 300mg tabs 3 12) 350g of an ointment containing 12.5% w/w of a single active ingredient has been prepared. The weight of active ingredient contained in 140g of the ointment is: 12.5g in 100g In 140g = (12.5 x140)/100 = 17.5g 17.5g 13) An ointment contains 15% of salicylic acid. How much salicylic acid is in 300g of ointment? 15g in 100g In 300g = 3 x 15 = 45g 45g 5 Calculations Workshop 1 14) Phytex paint contains 1.46% of salicylic acid, 4.89% of tannic acid and 3.12% of boric acid. How much salicylic acid is contained in a 25ml bottle? 1.46g in 100ml In 25ml = 1.46/4 = 0.365g 0.365g 15) What volume of a 30% paracetamol solution contains 1.5g of paracetamol? 30g in 100ml In 1.5g = (100/30)x 1.5 = 5ml 5ml 16) How much adrenaline is contained in a 1ml ampoule of adrenaline 1 in 1000 injection? 1g in 1000ml In 1ml = 1/1000 = 0.001g which is equiv to 1mg 1mg 17) How much Eumovate cream is required to produce 350g of a 1:4 dilution of Eumovate cream in aqueous cream? 1 to 4 is equiv to 1part in 5 parts 70g Eumovate in 350g 70g 18) The following is a formula for Mist Pot Cit. What volume of lemon spirit is required to make 150mls of Mist Pot Cit.? i. Potassium Citrate BP 300g ii. Citric Acid monohydrate BP 50g iii. Lemon spirit BP 5mls iv. Quillaia tincture BP 250mls v. Double strength chloroform water 300mls vi. Water for preparations. to 1000mls 5 Calculations Workshop 1 5ml to 1000ml For 150ml = (5 x 150)/1000 = 0.75ml 0.75mls 19) You are requested to prepare 300g of a 1 in 5 cream. How much of the active ingredient do you need? 1 part in 5 parts 60g in 300g 60g 20) You are requested to prepare 400g of a 1:4 cream. How much of the inert base cream do you need? 1:4 is 1part to 4 parts or 1part in 5 parts 80g active ingredient + 320g inert base 320g 21) You are asked to prepare 40g of a 1:4 parts of sulphur in White soft parafÏn. How much White soft parafÏn would you need? 1:4 1part in 5 parts 8g sulphur + 32g wsp 32g 22) You are asked to prepare a solution containing 1 in 1000 of potassium permanganate. How much potassium permanganate would be needed to make up 150ml? 1g in 1000ml In 150ml = 150/1000 = 0.15g ` 0.15g 5 Calculations Workshop 1 23) Diamorphine linctus BPC contains the following ingredients: Diamorphine Hydrochloride BP 0.6g Compound Tartrazine solution BP 12ml Glycerol BP 250ml Oxymel BP 250ml Syrup BP to 1000ml How much Diamorphine Hydrochloride is required to make up 200ml? 0.6g to 1000ml For 200ml = 0.6/5 = 0.12g 0.12g 24) If a solution contains 200mg of calcium carbonate in 500ml of vehicle. What is the concentration of the calcium carbonate, expressed as a percentage? 200mg in 500ml In 100ml = (200 x 100)/500 = 40mg which is equiv to 0.04g = 0.04%w/v 0.04% 25) If 400mg of potassium permanganate is dissolved in 2.5litres of water. What is the percentage strength of the resulting solution? 400mg in 2500ml In 100ml = (400 x 100)/2500 = 16mg which is equiv to 0.016g = 0.016%w/v 0.016% 26) A patient dissolves two tablets, each containing 300mg of aspirin, in 120ml of water. What is the aspirin concentration (%w/v) of the solution? 600mg in 120ml In 100ml = (600 x 100)/120 = 500mg which is equiv to 0.5g = 0.5%w/v 0.5% w/v 27) Nasacort contains 55mcg of triamcinolone per metered dose. How much of the active ingredient is contained in a 120 dose unit? 55mcg per dose x 120 doses = 6600mcg which is equiv to 6.6mg 6.6mg 5 Calculations Workshop 1 28) Lanoxin PG tablets contain 62.5 micrograms of digoxin, how many milligrams of digoxin are there in 500 tablets? 62.5mcg x 500 = 31250mcg which is equiv to 31.25mg ` 31.25mg 29) Epipen contains adrenaline 1 in 1000. How much adrenaline would be contained in seven 1ml vials? 1g in 1000ml In 1ml = 1/1000 In 7ml = 7/1000 = 0.007g which is equiv to 7mg 7mg 30) Potassium permanganate 0.2g Purified water to 100mls How many mls of a 5% w/v potassium permanganate solution could be used in place of the 0.2g in the above formula? 5g in 100ml In 0.2g = (0.2 x 100)/5 =4ml 4mls 5