Tutorial 4
Dilution and concentration
Equation:
Dilution: Q1 × C1 = Q2 × C2
𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑠𝑡𝑜𝑐𝑘 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 (%) 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
Stock solution: =
𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 (%) 𝑋 𝑚𝑙 𝑜𝑓 𝑠𝑡𝑜𝑐𝑘 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
Examples:
1. If 200 mL of a 10% v/v solution are diluted to 1200 mL, what will be the percentage
strength (v/v)?
200×10=1200×C2
=1.67%
2. How many milliliters of a 1:500 w/v stock solution should be used to make 2.5 liters of a
1:3000 w/v solution? 1:500 = 0.20%
1:2000 = 0.033%
2.5 L = 2500ml
0.20 (%) 2500
= 𝑋 𝑚𝑙 = 412.5ml
0.033 (%)
3. How many grams of a 1:10 trituration are required to obtain 20 mg of the drug?
10 g of trituration contain 1 g of drug
20 mg = 0.02 g
1 g ------------------------ 10g
0.02g ---------------------- xg
X = 0.2 g
4. What is the percentage of Betamethasone in an ointment prepared by mixing 5 g of 0.5%
ointment, 15 g of 1% ointment, and 30 g of 2% ointment?
0.005 × 5 g = 0.025 g
0.01 × 15 g = 0.15g
0.02 × 30 g = 0.6 g
Total 50 0.775
0.775 ÷ 50 = 0.0155
0.0155 × 100 = 1.55%
5. In what proportion should 2% Betamethasone ointment be mixed with an ointment base
to produce a 0.5% Betamethasone ointment?
Exercises:
1. How many grams of 10% w/w iodine solution can be made from 1500 g of 25% w/w
strong iodine solution?
Q1 × C1 = Q2 × C2. Q1×10=1500×25=
Q1=3.750g
2. If 400 mL of a 20% w/v solution were diluted to 2 liters, what would be the percentage
strength (w/v)?
Q1 × C1 = Q2 × C2
20×400=C2×2000=
C2=4%
3. If a pharmacist added 12 g of azelaic acid to 50 g of an ointment containing 15% azelaic
acid, what would be the final concentration of azelaic acid in the ointment?
Q1 × C1 = Q2 × C2
12×C2=50×15=
C2=62.5g. 12÷62.5×100=19.2%
4. How many milliliters of a 1:50 w/v boric acid solution can be prepared from 500 mL of a
5% w/v boric acid solution?
c1×v1=c2×v2
2×v1=500×5
v1=1250ml
5. How many milliliters of 5% w/v of aluminum acetate should be used in preparing 2 liters
of a 1:800 (w/v) solution?
1÷1800×100=0.125%
0.125__________200
5_______________x
X =80.000ml
6. How many milliliters of a 10% stock solution of a chemical is needed to prepare 120 mL
of a solution containing 10 mg of the chemical per milliliter?
c1×v1=c2×v2
10×v1=10×120. =120ml
7. How many milliliters of a 0.2% solution of a skin-test antigen must be used to prepare 4
mL of a solution containing 0.04 mg/mL of the antigen?
0.2÷100×1000=2mg/ml
c1×v1=c2×v2. 2×v1=0.04×4
=0.08mg/ml
8. How many grams of a 1:10 trituration is required to obtain 50 mg of the drug?
1g ___________10g
50g___________x. X=500g
9. A prescription calls for 0.005 g of morphine sulfate. How many milligrams of a 1:10
trituration may be used to obtain the morphine sulfate?
0.005×1000=5mg
1mg____________10
5mg____________X. X=50mg
10. Calculate the percentage of alcohol in a lotion containing 2 liters of alcohol 14%, 1 liter
of alcohol (95%), and enough boric acid solution to make 5 liters.
0.14×2=0.28. 0.95×1=0.95
total=1.23
calculate the % of alcohol in5liter=1.23÷5×100=24.6%
11. In what proportion should 5% and 1% hydrocortisone ointments be mixed to prepare a
2.5% ointment?
5% 1.5%part of 5% ointment
2.5%
1% 2.5%part of 1% ointment
12. If a pharmacist mixed 500ml of propylene glycol having a specific gravity of 1.20 with
500 mL of water, how many milliliters of additional propylene glycol should be added to
change the specific gravity to 1.15?
500×1.20=600ml. 500×1=500ml
1.15×X
total=600+500+(1.15×X)
student name:Hamida Fisal hassan
