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Seorang siswa melakukan percobaan dengan mencampurkan larutan NH4​OH dan HCl seperti pada tabel di bawah ini        Urutkan harga pH dari ketiga percobaan di atas, bila Kb​NH4​OH=10−5 dari yang terbesar hingga terkecil.

Pertanyaan

Seorang siswa melakukan percobaan dengan mencampurkan larutan begin mathsize 14px style N H subscript 4 O H end style dan begin mathsize 14px style H Cl end style seperti pada tabel di bawah ini
 

  
 

Urutkan harga pH dari ketiga percobaan di atas, bila begin mathsize 14px style K subscript italic b space N H subscript 4 O H equals 10 to the power of negative sign 5 end exponent end style dari yang terbesar hingga terkecil.

 

Pembahasan:

  1. pH percobaan 1. 

    begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell V subscript italic a cross times M subscript italic a cross times valensi end cell equals cell V subscript italic b cross times M subscript italic b cross times valensi end cell row cell 20 cross times 0 comma 1 cross times 1 end cell equals cell 20 cross times 0 comma 1 cross times 1 equals 2 space mmol end cell row blank blank blank row cell open square brackets N H subscript 4 Cl close square brackets end cell equals cell fraction numerator mol over denominator Volume space Campuran end fraction end cell row blank equals cell fraction numerator 2 space mmol over denominator 40 space mL end fraction end cell row blank equals cell 0 comma 05 space M end cell row blank blank blank row cell open square brackets H to the power of plus sign close square brackets end cell equals cell square root of K subscript italic w over K subscript italic b cross times open square brackets garam close square brackets 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 5 cross times 10 to the power of negative sign 2 end exponent 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 5 cross times 10 to the power of negative sign 2 end exponent end root end cell row blank equals cell square root of 50 cross times 10 to the power of negative sign 12 end exponent end root end cell row blank equals cell 7 comma 07 cross times 10 to the power of negative sign 6 end exponent end cell row blank blank blank 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 7 comma 07 cross times 10 to the power of negative sign 6 end exponent end cell row blank equals cell 6 minus sign log space 7 comma 07 end cell end table end style 
     
  2. pH pada percobaan 2

    begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell V subscript italic a cross times M subscript italic a cross times valensi end cell equals cell V subscript italic b cross times M subscript italic b cross times valensi end cell row cell 50 cross times 0 comma 2 cross times 1 end cell equals cell 50 cross times 0 comma 2 cross times 1 equals 10 space mmol end cell row blank blank blank row cell open square brackets N H subscript 4 Cl close square brackets end cell equals cell fraction numerator mol over denominator Volume space campuran end fraction end cell row blank equals cell fraction numerator 10 space mmol over denominator 100 space mL end fraction end cell row blank equals cell 10 to the power of negative sign 1 end exponent space M end cell row blank blank blank row cell open square brackets H to the power of plus sign close square brackets end cell equals cell square root of K subscript italic w over K subscript italic b cross times open square brackets garam close square brackets 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 10 to the power of negative sign 1 end exponent end root end cell row blank equals cell square root of 10 to the power of negative sign 10 end exponent end root end cell row blank equals cell 10 to the power of negative sign 5 end exponent end cell row blank blank blank 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 10 to the power of negative sign 5 end exponent end cell row blank equals 5 end table end style 
     
  3. pH pada percobaan 2

    begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell V subscript italic a cross times M subscript italic a cross times valensi end cell equals cell V subscript italic b cross times M subscript italic b cross times valensi end cell row cell 100 cross times 0 comma 05 cross times 1 end cell equals cell 100 cross times 0 comma 05 cross times 1 equals 5 space mmol end cell row blank blank blank row cell open square brackets N H subscript 4 Cl close square brackets end cell equals cell fraction numerator mol over denominator Volume space Campuran end fraction end cell row blank equals cell fraction numerator 5 space mmol over denominator 200 space mL end fraction end cell row blank equals cell 2 comma 5 cross times 10 to the power of negative sign 2 end exponent space M end cell row blank blank blank row cell open square brackets H to the power of plus sign close square brackets end cell equals cell square root of K subscript italic w over K subscript italic b cross times open square brackets garam close square brackets 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 2 comma 5 cross times 10 to the power of negative sign 2 end exponent end root end cell row blank equals cell square root of 25 cross times 10 to the power of negative sign 12 end exponent end root end cell row blank equals cell 5 cross times 10 to the power of negative sign 6 end exponent end cell row blank blank blank 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 5 cross times 10 to the power of negative sign 6 end exponent end cell row blank equals cell 6 minus sign log space 5 end cell end table end style 

Berdasarkan perhitungan di atas, semakin besar konsentrasi maka semakin kecil nilai pH nya.

Jadi, urutan harga pH dari ketiga percobaan di atas dari yang terbesar hingga terkecil adalah percobaan 3, 2, 1.

Jawaban terverifikasi

Dijawab oleh:

F. Krisna

Mahasiswa/Alumni Institut Pertanian Bogor

Terakhir diupdate 06 Oktober 2021

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