Roboguru

Tentukan pH berikut ini: 100 mL  0,1 M + 200 mL  0,1 M.

Pertanyaan

Tentukan pH berikut ini:

100 mL Ca open parentheses O H close parentheses subscript 2 0,1 M + 200 mL C H subscript 3 C O O H 0,1 M. K subscript italic a equals 10 to the power of negative sign 5 end exponent 

Pembahasan Soal:

Nilai pH campuran asam basa tersebut adalah sebagai berikut.

table attributes columnalign right center left columnspacing 0px end attributes row cell mol space Ca open parentheses O H close parentheses subscript 2 end cell equals cell V cross times M end cell row blank equals cell 100 space mL cross times 0 comma 1 space M end cell row blank equals cell 10 space mmol end cell row cell mol space C H subscript 3 C O O H end cell equals cell V cross times M end cell row blank equals cell 200 space mL cross times 0 comma 1 space M end cell row blank equals cell 20 space mmol end cell end table 

 

Reaksi tersebut membentuk garam bersifat basa, sehingga pH ditentukan dengan menggunakan rumus hidrolisis.

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 italic w over K subscript italic a cross times open square brackets garam close square brackets end root end cell row blank equals cell square root of K subscript italic w over K subscript italic a cross times fraction numerator mol space ion space terhidrolisis over denominator V space campuran end fraction end root end cell row blank equals cell square root of 10 to the power of negative sign 14 end exponent over 10 to the power of negative sign 5 end exponent cross times fraction numerator 10 space mmol cross times 2 over denominator 300 space mL end fraction end root end cell row blank equals cell square root of 66 cross times 10 to the power of negative sign 12 end exponent end root end cell row blank equals cell 8 comma 12 cross times 10 to the power of negative sign 6 end exponent end cell 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 blank equals cell negative sign log space 8 comma 12 cross times 10 to the power of negative sign 6 end exponent end cell row blank equals cell 6 minus sign log space 8 comma 12 end cell row blank blank blank row pH equals cell 14 minus sign pOH end cell row blank equals cell 14 minus sign left parenthesis 6 minus sign log space 8 comma 12 right parenthesis end cell row blank equals cell 8 plus log space 8 comma 12 end cell row blank blank blank end table 

Jadi, nilai pH campuran tersebut adalah 8+log 8,12. 

Pembahasan terverifikasi oleh Roboguru

Dijawab oleh:

F. Krisna

Mahasiswa/Alumni Institut Pertanian Bogor

Terakhir diupdate 07 Juni 2021

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Pertanyaan yang serupa

Hitunglah pH larutan :

Pembahasan Soal:

begin mathsize 14px style C H subscript 3 C O O Na end style merupakan senyawa garam yang terbentuk dari anion dari asam lemah dan kation dari basa kuat, sehingga dalam air mengalami hidrolisis parsial dan bersifat basa. Reaksi ionisasi garamnya adalah sebagai berikut.

C H subscript 3 C O O Na space rightwards arrow space C H subscript 3 C O O to the power of minus sign space plus space Na to the power of plus sign 


Untuk mengetahui pH larutan begin mathsize 14px style C H subscript 3 C O O Na end style 1 M begin mathsize 14px style left parenthesis K subscript a equals 1 cross times 10 to the power of negative sign 5 end exponent right parenthesis end style dapat ditentukan dengan cara :

  • Menghitung konsentrasi begin mathsize 14px style O H to the power of minus sign end style

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 M subscript anion end root end cell row blank equals cell square root of fraction numerator 1 cross times 10 to the power of negative sign 14 end exponent over denominator 1 cross times 10 to the power of negative sign 5 end exponent end fraction cross times 1 space M end root end cell row blank equals cell square root of 1 cross times 10 to the power of negative sign 9 end exponent space M end root end cell row blank equals cell 1 cross times 10 to the power of negative sign 4 comma 5 end exponent space M end cell end table 

  • Menghitung pOH

table attributes columnalign right center left columnspacing 0px end attributes row pOH equals cell negative sign log open square brackets O H to the power of minus sign close square brackets end cell row blank equals cell negative sign log left parenthesis 1 cross times 10 to the power of negative sign 4 comma 5 end exponent right parenthesis end cell row blank equals cell 4 comma 5 end cell end table

  • Menghitung pH

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 4 comma 5 end cell row blank equals cell 9 comma 5 end cell end table  


Jadi, pH larutan C H subscript bold 3 C O O Na adalah 9,5.undefined

0

Roboguru

Sebanyak 0,316 gram (CH3COO)2Ca (Mr = 158) dilarutkan dalam air hingga volumenya 1 liter. Jika Ka CH3COOH = 1 x  10-5, pH larutannya adalah ... .

Pembahasan Soal:

M r space equals space fraction numerator g r over denominator M r end fraction cross times fraction numerator 1000 over denominator V space left parenthesis m L right parenthesis end fraction space equals space fraction numerator 0 comma 316 space g r over denominator 158 space g r divided by m o l end fraction cross times 1000 over 1000 space equals space 2 cross times 10 to the power of negative 3 end exponent space M  left square bracket O H to the power of minus right square bracket equals square root of fraction numerator K w over denominator K a end fraction cross times left square bracket G right square bracket cross times v a l e n s i end root space equals space square root of 10 to the power of negative 14 end exponent over 10 to the power of negative 5 end exponent open square brackets 2 cross times 10 to the power of negative 3 end exponent close square brackets cross times 2 end root space equals space 2 cross times 10 to the power of negative 6 end exponent

pOH = - log[OH] = - log ( 2 x 10-6) = 6 – log 2

pH = 14 – pOH = 14 – (6 – log 2) = 8 + log 2

2

Roboguru

Manakah dari kedua larutan berikut yang memiliki pH lebih tinggi? (a) Larutan KF 0,1 M (b) Larutan 0,1 M

Pembahasan Soal:

begin mathsize 14px style open square brackets O H to the power of minus sign close square brackets equals square root of Kw over Ka x space M end root end style

(a) Larutan KF 0,1 M

Larutan ini adalah garam bersifat basa. begin mathsize 14px style Ka space H F equals 7 comma 2 space x space 10 to the power of negative sign 4 end exponent end style 

begin mathsize 14px style 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 fraction numerator 1 x 10 to the power of negative sign 14 end exponent over denominator 7 comma 2 space x 10 to the power of negative sign 4 end exponent end fraction end root x 10 to the power of negative sign 1 end exponent end cell row blank equals cell 1 comma 92 space x space 10 to the power of negative sign 6 end exponent end cell row pOH equals cell negative sign log left parenthesis 1 comma 92 space x space 10 to the power of negative sign 6 end exponent right parenthesis end cell row blank equals cell 6 minus sign log space 1 comma 92 end cell row blank equals cell 5 comma 71 end cell row pH equals cell 14 minus sign 5 comma 71 end cell row blank equals cell 8 comma 29 end cell end table end style    

pH dari larutan KF adalah 8,29.

 

(b) Larutan begin mathsize 14px style Ca F subscript 2 space end style0,1 M

Larutan ini adalah garam bersifat basa. begin mathsize 14px style Ka space H F equals 7 comma 2 space x space 10 to the power of negative sign 4 end exponent end style

begin mathsize 14px style Ca F subscript 2 yields Ca to the power of 2 plus sign and 2 F to the power of minus sign end style 

begin mathsize 14px style 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 fraction numerator 1 x 10 to the power of negative sign 14 end exponent over denominator 7 comma 2 x 10 to the power of negative sign 4 end exponent end fraction end root x space left parenthesis 2 x 10 to the power of negative sign 1 end exponent right parenthesis end cell row blank equals cell 1 comma 6 space x 10 to the power of negative sign 6 end exponent end cell row pOH equals cell negative sign log left parenthesis 1 comma 6 space x 10 to the power of negative sign 6 end exponent right parenthesis end cell row blank equals cell 5 comma 79 end cell row pH equals cell 14 minus sign 5 comma 79 end cell row blank equals cell 8 comma 21 end cell end table end style 

pH dari  larutan begin mathsize 14px style Ca F subscript 2 space end styleadalah 8,21.

Hasil menunjukkan bahwa  begin mathsize 14px style pH space K F greater than pH space Ca F subscript 2 end style.

Dengan demikian, nilai pH yang lebih tinggi adalah KF.

0

Roboguru

Di dalam 250 mL larutan terdapat 8,2 gram  yang terlarut. Jika nilai , maka pH larutan tersebut adalah ....

Pembahasan Soal:

begin mathsize 14px style C H subscript 3 C O O Na end style merupakan garam bersifat basa, perhitungan pH garamnya adalah:


begin mathsize 14px style Molaritas space C H subscript 3 C O O Na colon M equals massa over Mr cross times 1000 over pelarut M equals fraction numerator 8 comma 2 over denominator 82 end fraction cross times 1000 over 250 equals 0 comma 4 space M end style


begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell C H subscript 3 C O O Na end cell rightwards arrow cell C H subscript 3 C O O to the power of minus sign and Na to the power of plus sign end cell 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 middle dot M end root end cell row cell open square brackets O H to the power of minus sign close square brackets end cell equals cell square root of 10 to the power of negative sign 14 end exponent over 10 to the power of negative sign 5 end exponent middle dot 0 comma 4 end root 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 row pOH equals cell negative sign log left parenthesis 2 cross times 10 to the power of negative sign 5 end exponent right parenthesis equals 5 minus sign log 2 end cell row pH equals cell 14 minus sign left parenthesis 5 minus sign log 2 right parenthesis equals 9 plus log space 2 end cell end table end style  


Jadi, jawaban yang benar adalah E.space 

0

Roboguru

Nilai pH larutan  0,1 M jika diketahui  dan  adalah...

Pembahasan Soal:

Hidrolisis garam basa begin mathsize 14px style Na subscript 2 C O subscript 3 end style



Gunakan hanya begin mathsize 14px style Ka subscript 1 space H subscript 2 C O subscript 3 equals 4 comma 5 cross times 10 to the power of negative sign 7 end exponent space M end style karena nilai begin mathsize 14px style Ka subscript 2 end style terlalu kecil.


begin mathsize 14px style 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 begin inline style Kw over Ka end style cross times open square brackets G close square brackets end root end cell row blank equals cell square root of begin inline style fraction numerator 10 to the power of negative sign 14 end exponent over denominator 4 comma 5 cross times 10 to the power of negative sign 7 end exponent end fraction end style cross times 0 comma 1 space M end root end cell row blank equals cell square root of 0 comma 22 cross times 10 to the power of negative sign 8 end exponent end root space M end cell row blank equals cell 0 comma 48 cross times 10 to the power of negative sign 4 end exponent space M end cell end table end style


begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row pOH equals cell negative sign log space 0 comma 48 cross times 10 to the power of negative sign 4 end exponent end cell row blank equals cell 4 minus sign log space 0 comma 48 end cell row pH equals cell 14 minus sign left parenthesis 4 minus sign log space 0 comma 48 right parenthesis end cell row blank equals cell 10 plus log space 0 comma 48 end cell end table end style


Jadi, pH larutan adalah 10+log 0,48. Jawaban tidak tersedia di opsi jawaban.

0

Roboguru

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