Section 1: Calculating Percent Weight in Weight
If you know the amount of a component present and the mass of product involved, you can calculate the % w/w of the component.
Aqueous Calamine Cream BP 1988 contains 6 grams of Calamine in 150 grams of cream. What is the concentration % w/w of Calamine in the cream?
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Ratio Solution
You know that 150 g of cream contains 6 g of Calamine.
To find the % w/w you need to find what 100 g of creams contains.
By ratios:
150 g of cream contains 6 g of Calamine. Thus:
100 g of cream contains 100 x 6 g of Calamine
150
150 g of cream contains 6 g of Calamine. Thus:
100 g of cream contains 100 x 6 g of Calamine
150
100 g of creams contains 4 g of Calamine
The concentration of Calamine is 4 g/100 g ie 4 % w/w.
The concentration of Calamine is 4 g/100 g ie 4 % w/w.
Equation Solution
The equation you can use is:
% w/w = mass of solute x 100 (g/100 g)
mass of product
mass of product
% w/w Calamine = 6 x 100 (g/100 g)
150
150
% w/w Calamine = 4 (g/100 g)
The concentration of Calamine is 4 % w/w.
The concentration of Calamine is 4 % w/w.