Calculate the mass fraction of the solute if 12 g of salt was added to 68 g of water.

Given:
m (H2O) = 68g
m (salt) = 12g
Find: mass fraction of dissolved salt
Decision :
First of all, we can find the mass of the solution, meaning the formula
m (solution) = m (H2O) + m (salt)
m (solution) = 68 + 12 = 80 g
Now we can find the mass fraction of a dissolved substance, which we need to know using the formula
w (solution) = m (salt) * 100% / m (solution)
w (solution) = 12 * 100/80 = 15%
answer: w = 15%