Calculations that You Should Be Able to Do


The definition of percent weight in weight:

"The % w/w of any component is the number of grams of that component contained in 100 grams of the total product."

leads to the following equation:

% w/w = mass of solute x              100               (g/100 g)
mass of product

You need to be able to calculate all three parts of this equation
given two of the others ie you need to be able to calculate:

  1. percent weight in weight
  2. the mass of solute
  3. the total mass of a product
This part of the equation shows what proportion 100 grams of product is of the total mass of product present.

Once you know this proportion, you know that the same proportion of the total mass of component can be found in 100 grams of product.
% w/w = mass of solute x              100                       (g/100 g)
mass of product
For example.
Suppose 400 grams of a product contains 8 grams of a component.
100 grams is one quarter of the total mass of product present.
Thus 100 grams of product must contain one quarter of the total mass of component present ie 2 grams.
Thus the concentration of the component is 2 g/100 g ie 2 % w/w.
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