Question

when 5 grams of salt dissolve in 30 grams of water what is the resulting mass of the mixture?

Answer 1

35 g

Answer 2

As Bhaskar said, it'll be 35g. Because even though salt is dissolving in water, its mass remains intact. Its mass is not lowered or, for that matter, destroyed. A simple analogy would be, take 5g of water. heat it and turn it into vapour state. How much water vapour do you have now? 5g, right? What we're doing here is just re-positioning of the water molecules (in simple language, at least). The 'number' of water molecules is still the same, and hence the mass is, too.
Similarly (or not!), when salt is dissolved in water, its molecules are re-positioned (and that's why we don't see its crystal structure anymore). But, as the 'number' of the molecules does not change, its mass remains the same. Since the mass of a substance is the summation of mass of all its molecules (or nuclei, to be exact).
Hope this helped!

Answer 3

35