A diprotic acid (here symbolized by H2A) can undergo one or two dissociations depending on the pH. Each dissociation has its own dissociation constant, Ka1 and Ka2.
ɐ dɪpɹˈɑːɾɪk ˈæsɪd hˈɪɹ sˈɪmbəlˌaɪzd baɪ ˈeɪtʃ tˈuː ˈeɪ kæn ˌʌndɚɡˈoʊ wˈʌn ɔːɹ tˈuː dɪsˌoʊsɪˈeɪʃənz dᵻpˈɛndɪŋ ɔnðə pˈiː ˈeɪtʃ. ˈiːtʃ dɪsˌoʊsɪˈeɪʃən hɐz ɪts ˈoʊn dɪsˌoʊsɪˈeɪʃən kˈɑːnstənt, kˈɑː wˈʌn ænd kˈɑː tˈuː.