A student is asked to make up approx. 40.0 of a 29% (w/w) sucrose solution. Use Equation 2 from the introduction to calculate the g sucrose and the g water needed to make this solution.

Answer 1

By definition, a 29%-(w/w) sucrose solution contains 29 g of sucrose dissolved in 100 g of solution.

How much sucrose will be present in 40 g of this 29%-(w/w) sucrose solution?

40 g solution x (29 g sucrose / 100 g solution) = 11.6 g of sucrose

A solution consists of a solute (sucrose) and a solvent (water).

In a w/w-solution, the mass of the solvent is:

g of solution = g of sucrose + g of water

40 g = 11.6 g + x g of water

x g of water = 40 - 11.6 = 28.4 g water

To summarize, take 11.6 g of sucrose and dissolve it in 28.4 g of water to give 40 g of the 29%-(w/w) sucrose solution.