Dalam 500 mL larutan jenis kalsium Fluorida (CaF2) terdapat 8,2 mg CaF2. Tentukan kelarutan CaF2 dalam mol/L (Mr CaF2=78)

Dalam 500 mL larutan jenis kalsium Fluorida (CaF2) terdapat 8,2 mg CaF2. Tentukan kelarutan CaF2 dalam mol/L (Mr CaF2=78)

Jawaban : 2,1 x 10^-4 mol/liter

Mr CaF2 = 78 g/mol
V = 500 ml
m = 8,2 mg = 8,2 x 10^-3 g

Ditanya: s = … ?

Pembahasan:

Kelarutan (s) menyatakan jumlah maksimum zat terlarut yang dapat larut dalam suatu larutan. Kelarutan dapat dinyatakan dalam molaritas sebagai berikut:

s = (m / Mr) x (1000 / V)

Keterangan:
s : kelarutan (mol/liter)
m : massa zat terlarut (g)
Mr : massa molekul relatif zat terlarut (g/mol)
V : volume larutan (ml)

Maka diperoleh:

s = (m / Mr) x (1000 / V)
s = (8,2 x 10^-3 g / 78 g/mol) x (1000 / 500 ml)
s = (1,05 x 10^-4) x (2) mol/liter
s = 2,1 x 10^-4 mol/liter

Jadi, kelarutan CaF2 adalah 2,1 x 10^-4 mol/liter.

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