Because alkali metal sulfides are essentially salts of a weak acid and a strong base, they form basic solutions.
bɪkˈʌz ˈælkəlˌaɪ mˈɛɾəl sˈʌlfaɪdz ɑːɹ ᵻsˈɛnʃəli sˈɔlts əvə wˈiːk ˈæsɪd ænd ɐ stɹˈɔŋ bˈeɪs, ðeɪ fˈɔːɹm bˈeɪsɪk səlˈuːʃənz.