Does solute add to volume of solution?
Solute almost always changes the volume of final solution. The change (volume decrease or volume increase of final solution) of volume depends of solvent and solute chemicophysical properties, e.g. the full charge of each or the polar properties of each, or their molecular orbital structure and electron bond donors or acceptors. Two very non-interactive materials would not even mix, e.g. oil and water (H2O), though tiny tiny amounts of oil will &quot;dissolve&quot; in water as micelles, and tiny tiny amount of water will infiltrate oil, humidity of oil, just like humidity of breathable air.
If solute is not charged and does not have hydrogen-bonding-ready open orbitals or lone pairs of electrons, then the volume increases, both solute and solvent usually do not mix well.
If the solute is a ionic compound (e.g. salt, NaCl), then up to a certain amount of table salt the volume will decrease, the density will increase and reach the maximal amount of salt to reach the minimum amount of solvent, H2O, at a specific temperature and pressure.
If you mix a polar compound ready to accept or donate hydrogen bonds to H2O, then you get a similar picture as for NaCl in H2O, but not so drastic http://butane.chem.uiuc.edu/pshapley/genchem1/l21/vol.png , http://butane.chem.uiuc.edu/pshapley/genchem1/l21/1.html.