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Dalam 100 mL larutan  0,1 M mempunyai pH sama deng...

Dalam 100 mL larutan begin mathsize 14px style N H subscript 4 O H end style 0,1 M mempunyai pH sama dengan 100 mL larutan begin mathsize 14px style Ca open parentheses O H close parentheses subscript 2 space 5 cross times 10 to the power of negative sign 4 end exponent end style M. Kb undefined adalah ....undefined 

  1. begin mathsize 14px style 1 comma 8 cross times 10 to the power of negative sign 5 end exponent end styleundefined 

  2. begin mathsize 14px style 1 cross times 10 to the power of negative sign 5 end exponent end styleundefined 

  3. begin mathsize 14px style 1 comma 8 cross times 10 to the power of negative sign 3 end exponent end styleundefined 

  4. begin mathsize 14px style 1 cross times 10 to the power of negative sign 3 end exponent end styleundefined 

  5. begin mathsize 14px style 1 comma 8 cross times 10 to the power of negative sign 2 end exponent end styleundefined 

Jawaban:

Diketahui:
Larutan begin mathsize 14px style N H subscript 4 O H end style 0,1 M 100 mL mempunyai pH sama dengan 100 mL larutan begin mathsize 14px style Ca open parentheses O H close parentheses subscript 2 space 5 cross times 10 to the power of negative sign 4 end exponent end style M.

Ditanya:
Kb undefined

Jawab:
Kita harus menghitung pH Ca(OH)2 untuk dapat menghitung Ka NH4OH
Langkah-langkah penyelesaian:

1. Menghitung konsentrasi OH- larutan Ca(OH)2

Ca open parentheses O H close parentheses subscript 2 yields Ca to the power of 2 plus sign and 2 O H to the power of minus sign valensi space basa equals 2 

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 M subscript basa cross times valensi space basa end cell row blank equals cell left parenthesis 5 cross times 10 to the power of negative sign 4 end exponent right parenthesis cross times 2 end cell row blank equals cell 1 cross times 10 to the power of negative sign 3 end exponent space M end cell end table   

2. Menghitung pH larutan Ca(OH)2
table attributes columnalign right center left columnspacing 0px end attributes row pOH equals cell negative sign log space open square brackets O H to the power of minus sign close square brackets end cell row blank equals cell negative sign log space left parenthesis 1 cross times 10 to the power of negative sign 3 end exponent right parenthesis end cell row blank equals 3 end table  

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row pH equals cell 14 minus sign pOH end cell row blank equals cell 14 minus sign 3 end cell row blank equals 11 end table end style 

Jadi, pH begin mathsize 14px style Ca open parentheses O H close parentheses subscript 2 double bond N H subscript 4 O H equals 11 end style 

3. Menghitung konsentrasi OH- dari larutan NH4OH
table attributes columnalign right center left columnspacing 0px end attributes row pH equals 11 row pOH equals cell 14 minus sign pH end cell row pOH equals cell 14 minus sign 11 end cell row pOH equals 3 row blank blank blank row pOH equals cell negative sign log space open square brackets O H to the power of minus sign close square brackets end cell row 3 equals cell negative sign log space open square brackets O H to the power of minus sign close square brackets end cell row cell open square brackets O H to the power of minus sign close square brackets end cell equals cell 1 cross times 10 to the power of negative sign 3 end exponent space M end cell end table  


4. Menghitung nilai Kb dari NH4OH
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 Kb cross times Mb end root end cell row cell 1 cross times 10 to the power of negative sign 3 end exponent end cell equals cell square root of Kb cross times 0 comma 1 end root end cell row cell left parenthesis 1 cross times 10 to the power of negative sign 3 end exponent right parenthesis squared end cell equals cell Kb cross times left parenthesis 1 cross times 10 to the power of negative sign 1 end exponent right parenthesis end cell row cell 1 cross times 10 to the power of negative sign 6 end exponent end cell equals cell Kb cross times left parenthesis 1 cross times 10 to the power of negative sign 1 end exponent right parenthesis end cell row Kb equals cell fraction numerator 1 cross times 10 to the power of negative sign 6 end exponent over denominator 1 cross times 10 to the power of negative sign 1 end exponent end fraction end cell row Kb equals cell 1 cross times 10 to the power of negative sign 5 end exponent end cell end table   

Berdasarkan penjelasan diatas, diperoleh begin mathsize 14px style Kb space N H subscript 4 O H equals 1 cross times 10 to the power of negative sign 5 end exponent end style.

Jadi, jawaban yang benar adalah B.space 

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