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Pelajaran : Kimia
Kategori : Sifat Koligatif
Kata Kunci : larutan, fraksi mol zat terlarut, urea
Diketahui
Larutan urea 30%
Ditanya
Fraksi mol zat terlarut
Penyelesaian
Mr zat terlarut urea = 60
Mr pelarut air H₂O = 18
Larutan terdiri atas komponen zat terlarut dan pelarut
Anggap massa larutan = 100 gram
Massa zat terlarut urea = 30% x 100 gram ⇒ 30 gram
Massa zat pelarut air = 100 gram - 30 gram ⇒ 70 gram
Fraksi mol zat terlarut urea (Xt)
Xt = [mol urea] / [mol urea + mol air]
Xt = [³⁰/₆₀] / [³⁰/₆₀ + ⁷⁰/₁₈]
Xt = [³/₆] / [³/₆ + ⁷⁰/₁₈]
Xt = 9 / [9 + 70]
∴ Xt = ⁹/₇₉ atau 0,11
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Bila ditanyakan fraksi mol pelarut air (Xp):
Xp + Xt = 1
Xp = 1 - Xt
Xp = 1 - ⁹/₇₉
Xp = ⁷⁰/₇₉ atau 0,89