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Hitunglah pH larutan garam jika 4,1 gram garam CH3COONa dilarutkan dalam air sampai volume 250ml (Ar C=12,H=1,O=16,Na=23). (Kh=2x10^-9)

1 Jawaban

  • Mr CH3COONa = 4 Ar C + 3 Ar H + 2 Ar O + Ar Na
    Mr CH3COONa = 2(12) + 3(1) + 2(16) + 23
    Mr CH3COONa = 82

    n CH3COONa = massa / Mr
    n CH3COONa = 4,1 gram / 82
    n CH3COONa = 0,05 mol

    V = 250 mL = 0,25 L

    M = n / V
    M = 0,05 mol / 0,25 L
    M = 0,2 M

    CH3COONa => CH3COO^{-} + Na^{+}
    ........0,2 M.................0,2 M............ 0,2 M

    Garam ini merupakan Garam Basa karena terbuat dari asam lemah CH3COOH dan basa kuat NaOH
    Maka cari [OH-]

    [OH-] = √Kh × [CH3COO^{-}]
    [OH-] = √ 2 × 10^-9 × 0,2 M
    [OH-] = 2 × 10^-5

    pOH = - log [OH-]
    pOH = - log (2 × 10^-5)
    pOH = 5 - log 2

    pH = pKw - pOH
    pH = 14 - (5 - log 2)
    pH = 9 + log 2

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