There is 250g of 20% sodium nitrate solution. Determine the amount of salt substance in the solution.

In the problem we have: m (solution) = 250g; Sodium nitrite content in solution W (NaNO3) = 20%; it is necessary to find the amount of substance (NaNO3) in solution n (NaNO3) =?
In order to calculate the amount of a substance contained in a solution, we need to know its mass and molar mass n (NaNO3) = m (NaNO3) / M (NaNO3). We only know the molar mass (we find it according to the periodic table) M (NaNO3) = 85g / mol. Next, we are looking for the mass of the substance contained in the solution m (NaNO3) = 250 * 20/100 = 50g.
Now we have everything given and we find the amount of substance n (NaNO3) = 50/85 = 0.59 mol.