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