Cov khoom xyaw uas, raws li ionization, tawm los cations uas muaj tag nrho cov hydrogen ions (H⁺) yog hu ua acids; Tsis tas li ntawd, cov khoom uas yaj hauv dej thiab muaj peev xwm tso tawm cov protons los ua H₃O⁺ (hydronium ions) kuj tau muab cais ua cov kua qaub. Qhov siab dua qhov concentration ntawm H₃O⁺, qhov muaj zog acidity ntawm cov kua. H₃O⁺ ions muaj nyob hauv cov dej ntshiab, qhov twg lawv cov concentration sawv ntawm 10⁻⁷ mol / L. Qhov tshwm sim no tshwm sim los ntawm kev hloov ntawm protons los ntawm ib qho dej molecule mus rau lwm qhov. Hauv kev txiav txim siab ib txwm muaj, qhov concentration ntawm H₃O⁺ kuj tseem suav tias yog nyob ntawm qhov concentration ntawm hydrogen ions, txawm hais tias feem ntau ntawm hydrogen ions hauv cov tshuaj aqueous muaj nyob rau hauv daim ntawv ntawm H₃O⁺.
Hauv chemistry, lub ntsiab lus nqaim ntawm cov kua qaub yog: ib qho sib xyaw uas, thaum yaj hauv cov kua dej aqueous, nkag mus rau ionization kom yield cations uas muaj tsuas yog hydrogen ions. Tawm tswv yim los ntawm Arrhenius, lub theoretical moj khaum no hu ua Arrhenius acid-base theory.
