15 g of starch with heating was dissolved in 285 g of water. Mass fraction of starch in the resulting solution will be (%) …

The mass fraction of a component in a solution is calculated as the ratio of the mass of this component to the mass of the entire solution and is expressed as a percentage or fractions:

Let us designate the mass fraction – w, the mass of starch – m (k), the mass of water – m (in), the mass of the solution – m (solution).

w = (m (k) / m (solution)) * 100% (1)

The mass of the solution m (solution) is the mass of all its components, that is, in our case, this is the mass of starch and water:

m (p-pa) = m (k) + m (in) (2)

Substitute the expression for the mass of the solution from formula (2) into formula (1), and we get:

w = (m (k) / (m (k) + m (w)) * 100% = (15 / (15 + 285)) * 100% = 5%

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