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Tentukan H+, OH−, pH dan pOH dari 6,1 gram HCO3​ (diket Ar H= 1, Ar = 12, Ar O = 16 ) dilarutkan sampai volum 500 mL.

Pertanyaan

Tentukan H to the power of plus sign, O H to the power of minus sign, pH dan pOH dari 6,1 gram H C O subscript 3 (diket Ar H= 1, Ar = 12, Ar O = 16 ) dilarutkan sampai volum 500 mL.

S. Lubis

Master Teacher

Jawaban terverifikasi

Jawaban

pada senyawa H subscript 2 C O subscript 3 tersebut, nilai konsentrasi ion H to the power of plus sign nya adalah 2 comma 9 cross times 10 to the power of negative sign 4 end exponent sedangkan konsentrasi ion O H to the power of minus sign nya 3 comma 45 cross times 10 to the power of negative sign 10 end exponent , sehingga nilai pH nya yaitu 4negative signlog2,9 dan pOH nya 10+log2,9 .

Pembahasan

Senyawa pada soal kurang tepat, kemungkinan yang dimaksud adalah H subscript 2 C O subscript 3 bukan H C O subscript 3.
H subscript 2 C O subscript 3 merupakan asam lemah dengan nilai Ka nya 4 comma 3 cross times 10 to the power of negative sign 7 end exponent. Dari data Ar yang diketahui maka Mr H subscript 2 C O subscript 3 = 62 .
Konsentrasi nya dapat ditentukan dengan cara:

  • cari mol terlebih dahulu
    table attributes columnalign right center left columnspacing 0px end attributes row cell italic n subscript H subscript 2 C O subscript 3 end subscript end cell equals cell fraction numerator italic m italic a italic s italic s italic a over denominator Mr end fraction end cell row blank equals cell fraction numerator 6 comma 1 over denominator 62 end fraction end cell row blank equals cell 0 comma 098 space almost equal to space 0 comma 1 space mol end cell end table
  • hitung konsentrasinya
    M subscript H subscript 2 C O subscript 3 space equals space n over V end subscript equals space fraction numerator 0 comma 1 over denominator 0 comma 5 space L end fraction equals space 0 comma 2 space Molar

Selanjutnya menentukan konsentrasi H to the power of plus sign dalam larutan tersebut yaitu:
table attributes columnalign right center left columnspacing 0px end attributes row cell open square brackets H to the power of plus sign close square brackets end cell equals cell square root of Ka cross times M end root end cell row blank equals cell square root of 4 comma 3 cross times 10 to the power of negative sign 7 end exponent cross times 0 comma 2 end root end cell row blank equals cell space square root of 4 comma 3 cross times 10 to the power of negative sign 7 end exponent cross times 2 cross times 10 to the power of negative sign 1 end exponent end root end cell row blank equals cell square root of 8 comma 6 cross times 10 to the power of negative sign 8 end exponent end root end cell row blank equals cell 2 comma 9 cross times 10 to the power of negative sign 4 end exponent space end cell end table

Selanjutnya menentukan pH dalam larutan yaitu:
table attributes columnalign right center left columnspacing 0px end attributes row pH equals cell negative sign log space open square brackets H to the power of plus sign close square brackets end cell row blank equals cell negative sign log space 2 comma 9 cross times 10 to the power of negative sign 4 end exponent end cell row blank equals cell 4 minus sign log space 2 comma 9 end cell end table

sehingga nilai pOH nya:space
table attributes columnalign right center left columnspacing 0px end attributes row pOH equals cell 14 minus sign pH end cell row blank equals cell 14 minus sign left parenthesis 4 minus sign log space 2 comma 9 right parenthesis end cell row blank equals cell 10 plus log space 2 comma 9 end cell end table

Kemudian menentukan konsentrasi O H to the power of minus sign dalam larutan tersebut gunakan persamaan tetapan kesetimbangan air (Kw) :
table attributes columnalign right center left columnspacing 0px end attributes row cell open square brackets H to the power of plus sign close square brackets middle dot open square brackets O H to the power of minus sign close square brackets end cell equals cell K subscript w end cell row cell open square brackets H to the power of plus sign close square brackets middle dot open square brackets O H to the power of minus sign close square brackets end cell equals cell 10 to the power of negative sign 14 end exponent end cell row cell open square brackets 2 comma 9 cross times 10 to the power of negative sign 4 end exponent close square brackets middle dot open square brackets O H to the power of minus sign close square brackets end cell equals cell 10 to the power of negative sign 14 end exponent end cell row cell open square brackets O H to the power of minus sign close square brackets end cell equals cell fraction numerator 10 to the power of negative sign 14 end exponent over denominator 2 comma 9 cross times 10 to the power of negative sign 4 end exponent end fraction end cell row cell open square brackets O H to the power of minus sign close square brackets end cell equals cell 3 comma 45 cross times 10 to the power of negative sign 10 end exponent end cell end table


Jadi, pada senyawa H subscript 2 C O subscript 3 tersebut, nilai konsentrasi ion H to the power of plus sign nya adalah 2 comma 9 cross times 10 to the power of negative sign 4 end exponent sedangkan konsentrasi ion O H to the power of minus sign nya 3 comma 45 cross times 10 to the power of negative sign 10 end exponent , sehingga nilai pH nya yaitu 4negative signlog2,9 dan pOH nya 10+log2,9 .

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