In an experiment, 1 mol kcl is dissolved in a 1.4-kg sample of water, then 1 mol glucose is dissolved in another 1.4-kg sample of water. why does the kcl solution have the higher boiling point?

Because presence of non-volatile substances (salt-KCl) decreases its mole fraction and the solution's volatility (tendency of a substance to vaporize) and in that way raises the normal boiling point in proportion to the concentration of the solutes (KCl). This is called boiling point elevation (solution has a higher boiling point than a pure solvent). Example is salt water (boils at a higher temperature than pure water).

The mass has escaped into a gas which you can not see so the law stays true.