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Pertanyaan

Suatu larutan HCN 0,1 M mempunyai pH sebesar 3 – log 2, berapa gram kalium sianida yang terlarut dalam 500 space cm cubed larutan agar diperoleh pH sebesar 9 + log 2? (Ar K = 39; C = 12; dan N = 14).

D. Santika

Master Teacher

Mahasiswa/Alumni Universitas Pendidikan Indonesia

Jawaban terverifikasi

Jawaban

 gram kalium sianida yang terlarut dalam 500 space cm cubed larutan adalah 52 gram.

Pembahasan

Menghitung nilai Ka HCN 0,1 M berdasarkan nilai pH:

table attributes columnalign right center left columnspacing 0px end attributes row pH equals cell 3 minus sign log space 2 end cell row cell open square brackets H to the power of plus sign close square brackets end cell equals cell 2 cross times 10 to the power of negative sign 3 end exponent end cell end table 

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 K subscript a cross times M end root end cell row cell 2 cross times 10 to the power of negative sign 3 end exponent end cell equals cell square root of K subscript a cross times 0 comma 1 end root space space space left parenthesis italic k italic u italic a italic d italic r italic a italic t italic k italic a italic n space italic k italic e italic d italic u italic a space italic r italic u italic a italic s right parenthesis end cell row cell open parentheses 2 cross times 10 to the power of negative sign 3 end exponent close parentheses squared end cell equals cell open parentheses square root of K subscript a cross times 0 comma 1 end root close parentheses squared end cell row cell 4 cross times 10 to the power of negative sign 6 end exponent end cell equals cell K subscript a cross times 0 comma 1 end cell row cell K subscript a end cell equals cell fraction numerator 4 cross times 10 to the power of negative sign 6 end exponent over denominator 0 comma 1 end fraction equals 4 cross times 10 to the power of negative sign 5 end exponent end cell end table 

Hidrolisis garam adalah reaksi antara air dan ion-ion yang berasal dari asam lemah atau basa lemah suatu garam.

Kalium sianida (KCN) merupakan garam yang terdiri dari basa kuat (kation) dan asam lemah (anion), reaksi ionisasi garam sebagai berikut:

K C N yields K to the power of plus sign and C N to the power of minus sign     

Sehingga reaksi hidrolisis yang terjadi adalah:

 K to the power of plus sign and H subscript 2 O equilibrium left parenthesis tidak space terjadi space reaksi right parenthesis C N to the power of minus sign and H subscript 2 O equilibrium H C N and O H to the power of minus sign     

Dengan demikian, garam tersebut bersifat basa. Ubah nilai pH ke dalam bentuk O H to the power of minus sign:

table attributes columnalign right center left columnspacing 0px end attributes row pH equals cell 9 plus log space 2 end cell row pOH equals cell 14 minus sign pH end cell row blank equals cell 14 minus sign left parenthesis 9 plus log space 2 right parenthesis end cell row blank equals cell 5 minus sign log space 2 end cell row cell open square brackets O H to the power of minus sign close square brackets end cell equals cell 2 cross times 10 to the power of negative sign 5 end exponent end cell end table 

Nilai M garam KCN dapat dihitung melalui:

table attributes columnalign right center left columnspacing 0px end attributes row cell open square brackets O H to the power of minus sign close square brackets end cell equals cell square root of K subscript w over K subscript a cross times open square brackets C N to the power of minus sign close square brackets end root end cell row cell open square brackets 2 cross times 10 to the power of negative sign 5 end exponent close square brackets end cell equals cell square root of fraction numerator 10 to the power of negative sign 14 end exponent over denominator 4 cross times 10 to the power of negative sign 5 end exponent end fraction cross times open square brackets C N to the power of minus sign close square brackets end root space space space left parenthesis kuadratkan space kedua space ruas right parenthesis end cell row cell open square brackets 2 cross times 10 to the power of negative sign 5 end exponent close square brackets squared end cell equals cell open parentheses square root of fraction numerator 10 to the power of negative sign 14 end exponent over denominator 4 cross times 10 to the power of negative sign 5 end exponent end fraction cross times open square brackets C N to the power of minus sign close square brackets end root close parentheses squared end cell row cell 4 cross times 10 to the power of negative sign 10 end exponent end cell equals cell fraction numerator 10 to the power of negative sign 14 end exponent over denominator 4 cross times 10 to the power of negative sign 5 end exponent end fraction cross times open square brackets C N to the power of minus sign close square brackets end cell row cell open square brackets C N to the power of minus sign close square brackets end cell equals cell fraction numerator 4 cross times 10 to the power of negative sign 10 end exponent space. space 4 cross times 10 to the power of negative sign 5 end exponent over denominator 10 to the power of negative sign 14 end exponent end fraction end cell row blank equals cell 16 cross times 10 to the power of negative sign 1 end exponent end cell row blank equals cell 1 comma 6 space M end cell row cell open square brackets C N to the power of minus sign close square brackets end cell equals cell open square brackets K C N close square brackets end cell end table 

menghitung gram garam KCN:

table attributes columnalign right center left columnspacing 0px end attributes row M equals cell gram over Mr cross times 1000 over mL end cell row cell 1 comma 6 end cell equals cell fraction numerator gram over denominator left parenthesis 39 plus 12 plus 14 right parenthesis end fraction cross times 1000 over 500 end cell row cell 1 comma 6 end cell equals cell gram over 65 cross times 2 end cell row gram equals cell fraction numerator 1 comma 6 cross times 65 over denominator 2 end fraction end cell row blank equals cell 52 space gram end cell end table 

Jadi gram kalium sianida yang terlarut dalam 500 space cm cubed larutan adalah 52 gram.

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