Question

1) What is the percentage of alcohol in the following prescription? Rx Chloroform Spirit 110.0 mL (88% alcohol) Aromatic Elixir 85.0 mL (22% alcohol) Terpin Hydrate Elixir 255.0 mL (40% alcohol) Sig. 5 mL for cough

2) In what proportions should 10% and 4% zinc oxide ointments be mixed to prepare a 6% ointment? How much of the 6% can be made using 1 pound of the 10%?

3) If 200 ml of a 10% (w/v) solution are diluted to 2 liters, what will be the percentage strength?

4) How many milliliters of a syrup having a specific gravity of 1.50 should be mixed with 2000 mL of a syrup having a specific gravity of 1.25 to obtain a product having a specific gravity of 1.30?

5) A pharmacist mixes 100 ml of 35% (w/w) hydrochloric acid with enough purified water to make 400 ml. If the specific gravity of HCl is 1.2, calculate the percentage strength (%w/v) of the final solution.

Answer 1

1. Percentage of alcohol=> total alcohol in solution/total volume of solution=>( 0.88*110ml +0.22*85ml+0.4*255ml)/(110+85+255)ml

=> (96.8 + 18.7+ 102)/450=> 217.5/450=> 48.3%

2. Let proportion of mixing be x.

then, x*0.1+1*0.04= (x+1)*0.06

=> 0.1x+ 0.04= 0.06x+0.06

=> 0.04x = 0.02

=> x= 0.5

Hence, proportion of mixing has to be 1:2 for 10% and 4% ointments.

Using 1 pound of 10%, we can make 3 pound total of 6%.( using the calculated proportion)

3. 10% w/v solution. The weight of the solute will remain the same. Hence, percentage strength will become 10% w/v * 200ml/ 2000ml=> 1% w/v solution.

4. Let the number of milliliters be x ml.

Then, x *1.50+2000*1.25=(x+2000)*1.30

=> 1.50x + 2500= 1.30x + 2600

=> 0.20x = 100

=> x= 500 ml