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Question 1 of 3

A moist crude drug contains 8.9% w/w of the active ingredient and 27.3% w/w of water. What will be the concentration % w/w of the active ingredient after the drug is dried? Answer to 1 decimal place.
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% w/w
The concentration of the active drug will be 12.2% w/w.
  1. The given concentrations for the moist drug mean that:
    100 g of moist drug contains 8.9 g of the active ingredient and 27.3 g of water.
  2. Considering 100 g of the moist drug.
    Drying removes 27.3 g of water which means that after drying there are:
    100 - 27.3 g = 72.7 g of dried crude drug left.
    The amount of active ingredient present is unchanged ie still 8.9 g.
  3. The 72.7 g of dried crude drug contains 8.9 g of the active ingredient. Thus:
    100 g of dried crude drug contains 100/72.7 x 8.9 g of the active ingredient.
    100 g of dried crude drug contains 12.24 g of the active ingredient.
    The concentration of the active ingredient is 12.24 g/100g = 12.2 % w/w to 1 dec pl

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Question 2 of 3

How many grams of Benzoic Acid should be added to 250g of an ointment containing 0.3% w/w Benzoic Acid to prepare an ointment containing 0.6% w/w Benzoic Acid? Answer to 2 decimal places.
Type in your answer and PRESS ENTER.
grams
0.75 grams of Benzoic Acid would need to be added.
  1. Find the mass of base in the ointment. A concentration of 0.3 % w/w means that:
    100 g of ointment contains 0.3 g of Benzoic Acid. Thus:
    250 g of ointment contains 250/100 x 0.3 g = 0.75 g of Benzoic Acid.
    Mass of Base = Total Mass - mass of Benzoic Acid = 250 - 0.75 g = 249.25 g
  2. Find the total mass of ointment required.
    The required concentration of Benzoic Acid is 0.6 % w/w which means that the concentration of the base is 100 - 0.06 % w/w = 99.4 % w/w. You know that:
    99.4 % of the ointment has a mass of 249.25 g. Thus:
    100 % of the ointment has a mass of 100/99.4 x 249.25 g = 250.754 g
  3. Find the mass of Benzoic Acid in the 250.75 g of ointment.
    Mass of Benzoic Acid = Total Mass - Mass of Base = 250.754 - 249.25 g = 1.504 g
  4. Find the mass of Benzoic Acid that should be added, to 2 decimal places.
    Mass of Benzoic Acid = Total Mass - Mass Already Present = 1.504 - 0.75 g = 0.75 g

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Question 3 of 3

A sample of opium contains 36% w/w water and 14% w/w Morphine. How many grams of Morphine could be obtained from 120grams of the dry opium? Answer to 2 decimal places.

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grams
26.25g of Morphine could be obtained.

The given concentrations tell you that:
100 g of wet opium contains 36 g of water and 14 g of Morphine.

Considering 100 g of wet opium.
Drying removes 36 g of water but the amount of Morphine
present stays the same ie 14 g. Thus:
100 - 36 g = 64 g of dried opium contains 14 g of Morphine.
So:
64 g of dry opium contains 14 g of Morphine. Thus:
120g of dry opium contains 120 / 64 x 14 g = 26.250 g of Morphine.
26.25 g (to 2 dec pl) of Morphine could be obtained from 120 g.

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