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Question 1 of 9

Aqueous Calamine Cream contains 0.5 % w/w Phenoxyethanol. What is the amount of cream that contains 600 mg of Phenoxyethanol?

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grams
120 grams of cream contain 600 mg of Phenoxyethanol.
EITHER
Convert milligrams to grams: 600 mg = 0.6 g
mass of product = mass of component x     100     g
% w/w
mass of cream = 0.6 x 100 g
0.5
mass of cream = 120 g
OR
 0.5 % w/w Phenoxyethanol means that there are
0.5 g of Phenoxyethanol in 100 g of cream
Thus: 0.6 g of Phenoxyethanol are in 0.6 x 100 g of cream
0.5
0.6 g of Phenoxyethanol are in 120 g of cream

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Question 2 of 9

You need to prepare 650 g of Calamine and Coal Tar Ointment BP 1988 containing 2.5 % w/w Strong Coal Tar Solution. How much Strong Coal Tar Solution do you need to weigh out?

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grams
You need to weigh out 16.25 grams of Strong Coal Tar Solution.

EITHER
 mass of component = % w/w x mass of product   g
100
mass of Strong Coal Tar Solution = 2.5 x 650   g
100
mass of Strong Coal Tar Solution = 16.25 g
OR
 2.5 % w/w Strong Coal Tar Solution means that:
100 g of ointment contains 2.5 g of Strong Coal Tar Solution
Thus: 650 g of ointment contains 650 x 2.5 g of Strong Coal Tar Solution
100
650 g of ointment contains 16.25 of Strong Coal Tar Solution

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Question 3 of 9

Salicylic Acid Ointment BP 1988 contains 2.0 % w/w Salicylic Acid, and a water emulsifying basis only. What mass of the basis is needed to prepare 65 grams of the Ointment?

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grams
63.7 grams of the basis are needed.
You can approach this problem in 2 ways:
1 Work out the mass of Salicylic Acid needed. The amount of water emulsifying basis needed is then 65 g less the mass of Salicylic Acid. Mass of Salicylic Acid needed:
2.0 % w/w Salicylic Acid means that:
100 g of ointment contains 2 g of Salicylic Acid
65 g of ointment contains  65   x 2 = 1.3 g of Salicylic Acid
100
Therefore mass of water emulsifying basis = 65 - 1.3 = 63.7 grams
2 Because you know that the ONLY other component is the water emulsifying basis, you can calculate its % w/w and calculate the mass from this. % w/w = 100 - 2.0 = 98
98 % w/w water emulsifying basis means that:
100 g of ointment contains 98 g of basis
65 g of ointment contains  65   x 98 = 63.7 grams of basis
100

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Question 4 of 9

Compound Aluminium Powder BP 1988 contains 20 % w/w Aluminium Powder and 40 % w/w Zinc Oxide. A pharmacist makes up 900 g of the Powder. What is the combined mass of Aluminium Powder and Zinc Oxide contained in the Powder?

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grams
The combined mass of Aluminium Powder and Zinc Oxide is 540 grams.
Combined mass
= 180 + 360 g
= 540 g
EITHER
 mass of component = % w/w x mass of product    g
100
mass of Aluminium Powder = 900 x    20       g = 180 g
100
mass of Zinc Oxide             = 900 x    40       g = 360 g
100
Combined mass
= 180 + 360 g
= 540 g
OR
 20 % w/w Aluminium Powder means that:
100 g of Powder contains 20 g of Aluminium Powder
900 g of Powder contains 900  x 20 g = 180 g of Aluminium Powder
100
40 % w/w Zinc Oxide means that:
100 g of Powder contains 40 g of Zinc Oxide
900 g of Powder contains 900 x 40 g = 360 g of Zinc Oxide
100

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Question 5 of 9

A spray which kills flying insects contains 0.7 % w/w Tetramethrin. If it takes 1.4 mg of Tetramethrin to kill a fly, how many grams of spray are needed to kill 10 flies - assuming that 100 % of the spray goes on the flies?

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grams
2 grams of spray are needed.
EITHER
Convert milligrams to grams: 1.4 mg = 0.0014 g
To kill one fly:
mass of product = mass of component x   100   g
% w/w
mass of spray = 0.0014 x 100 g
0.7
mass of spray = 0.2 g
Therefore spray needed to kill 10 flies is 10 x 0.2 g = 2 grams
OR
 To kill 1 fly:
0.7 % w/w Tetramethrin means that there are
0.7 g of Tetramethrin in 100 g of spray
Thus: 0.0014 g of Tetramethrin are in 0.0014 x 100 g = 0.2 g of spray
0.7
Therefore spray needed to kill 10 flies is 10 x 0.2 g = 2 grams

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Question 6 of 9

200 ml of Sodium Acid Phosphate BP Solution contains 6.45 g of Sodium Acid Phosphate BP. If the density of the solution is 1.008 g/ml, what is the concentration % w/w of the Solution - to one decimal place?

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% w/w
The concentration of the Sodium Acid Phosphate BP Solution is 3.2 % w/w.
To find the concentration you need to find the number of grams in 100 g of Solution. You are told that there are 6.45 g in 200 ml of Solution. You must therefore find out how much 200 ml of Solution weighs. You can do this by using the density, 1.008 g/ml.
EITHER
1 ml of Solution has a mass of 1.008 grams. Thus:
200 ml of Solution has a mass of 200/1 x 1.008 g = 201.6 g
% w/w = mass of component x          100                (g/100 g)
mass of product
% w/w of Solution = 6.45 x    100   = 3.19 = 3.2 g/100 g = 3.2 % w/w
201.6
OR
 201.6 g of Solution contains 6.45 g of Sodium Acid Phosphate BP
100 g of Solution contains    100    x 6.45 g = 3.19 g = 3.2 g (one decimal place)
201.6
Concentration is 3.2 g/100 g = 3.2 % w/w
To find the concentration you need to find the number of grams in 100 g of Solution. You are told that there are 6.45 g in 200 ml of Solution. You must therefore find out how much 200 ml of Solution weighs. You can do this by using the density, 1.008 g/ml, which means that:
1 ml of Solution weighs 1.008 g

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Question 7 of 9

How many kilograms (to 2 decimal places) of sucrose are there in 1.5 litres of Syrup BP if the concentration of sucrose in the Syrup is 66.7 % w/w and the density of the Syrup is 1.332 g/ml?

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kg
There are 1.33 kg of sucrose in 1.5 litres of Syrup.
You are given the concentration of the Syrup as 66.7 % w/w ie as a weight in weight. Therefore you know that 100 g of Syrup contains 66.7 g of sucrose. You need to find the mass of sucrose in 1.5 litres of Syrup: you must therefore convert this volume to a mass. You can do this by using the density.
Convert litres to millilitres: 1.8 l = 1800 ml and then look at the density.
1 ml of Syrup has a mass of 1.332 g. Thus:
1500 ml of Syrup has a mass of 1500/1 x 1.332 g = 1998 g
66.7 % w/w sucrose means that
100 g of Syrup contains 66.7 g of sucrose
1998 g of Syrup contains 1998 x 66.7 g of sucrose
100
1998 g of Syrup contains 1332 g of sucrose
1998 g of Syrup contains 1.33 kg of sucrose to 2 decimal places.
You are given the concentration of the Syrup as 66.7 % w/w ie as a weight in weight. Therefore you know that 100 g of Syrup contains 66.7 g of sucrose. You need to find the mass of sucrose in 1.5 litres of Syrup: you must therefore convert this volume to a mass. You can do this by using the density, 1.332 g/ml which tells you that:
1 ml of Syrup has a mass of 1.332 g.

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answer or click on the Answer button to have a look at the answer.

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Question 8 of 9

75 g of Compound Benzoic Acid Ointment BP 1988 contains 4.5 g of Benzoic Acid and 3 % Salicylic Acid. The only other component is Emulsifying Ointment. What is the % w/w of the Emulsifying Ointment?

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% w/w
The concentration of the Emulsifying Ointment is 91 % w/w.
     There are 2 approaches:
  1. Find out the % w/w of Benzoic Acid. The % w/w of Emulsifying Ointment is then 100
    less the % w/w of Benzoic Acid and of Salicylic Acid.
    % w/w Benzoic Acid = mass of component x            100            g / 100 g
    mass of product
    % w/w Benzoic Acid = 4.5 x 100/75 g = 6 %
    Therefore the % w/w of Emulsifying Ointment is 100 - (6 + 3) = 91 % w/w
  2. Find how much Salicylic Acid is present. Then find out how much Emulsifying Ointment is present: this is the total mass less the mass of Benzoic Acid and Salicylic Acid. Then calculate the % w/w:
    mass of Salicylic Acid = mass of product x % w/w = 75 x    3    = 2.25 g
    100100
    Therefore mass of Emulsifying Ointment = 75 - (4.5 +2.25) g = 68.25 g in 75 g of ointment
    Concentration of Emulsifying Ointment = 68.25 g/75 g = 91 g/100 g = 91 % w/w

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Question 9 of 9

How many grams (to one decimal place) of Sodium Acid Phosphate BP are there in 500 ml of Sodium Acid Phosphate BP Solution if the concentration of the Sodium Acid Phosphate BP in the Solution is 3.2 % w/w and the density of the solution is 1.008 g/ml?

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grams
There are 16.1 grams of Sodium Acid Phosphate BP in the Solution.
You are given the concentration in terms of percentage weight in WEIGHT but the amount of solution involved is given in millilitres ie as a volume. You need to convert the volume into a mass in grams - you can use the density to do this.
Considering the density of 1.008 g/ml:
1 ml of Solution has a mass of 1.008 grams. Thus:
500 ml of Solution has a mass of 500/1 x 1.008 g = 504 grams
3.2 % w/w Sodium Acid Phosphate BP means that:
100 g of Solution contains 3.2 g of Sodium Acid Phosphate BP
504 g of Solution contains 504 x 3.2 = 16.12 g
100
504 g of Solution contains 16.1 g (to one decimal place)
You are given the concentration in terms of percentage weight in WEIGHT but the amount of solution involved is given in millilitres ie as a volume. You need to convert the volume into a mass in grams - you can use the density to do this. A density of 1.008 g/ml means that:
1 ml of Solution has a mass of 1.008 grams.

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an answer or you can click on the Answer button to see the answer.

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