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Seorang siswa mencampurkan asam lemah CH 3 ​ COOH 0,1 M ( K a ​ = 1 0 − 5 ) sebanyak 50 mL dengan basa kuat NaOH 0,1 M. Hitung pH larutan pada saat : Setelah ditambah 50 mLNaOH 0,1 M Setelah ditambah 60mLNaOH 0,1 M Setelah ditambah 75mLNaOH 0,1 M

Seorang siswa mencampurkan asam lemah  0,1 M () sebanyak 50 mL dengan basa kuat NaOH 0,1 M. Hitung pH larutan pada saat :

  • Setelah ditambah 50 mL NaOH 0,1 M
  • Setelah ditambah 60 mL NaOH 0,1 M
  • Setelah ditambah 75 mL NaOH 0,1 M

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J. Siregar

Master Teacher

Mahasiswa/Alumni Universitas Negeri Medan

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Jawaban

pH campuran setelah penambahan NaOH 0,1 M secara berturut-turut adalah 8 + log 7, 11 + log 9, dan 12 + log 1,6.

pH campuran setelah penambahan NaOH 0,1 M secara berturut-turut adalah 8 + log 7, 11 + log 9, dan 12 + log 1,6.

Pembahasan

Penentuan pH campuran sebagai berikut. Penambahan 50 mL NaOH 0,1 M berarti jumlah mol asam lemah dan basa kuat tepat habis bereaksi sehingga terbentuk garam. Setelah ditambah 60 mLNaOH 0,1 M Bersisa basa kuat NaOH sebanyak 1 mmol sehingga perhitungan pH campuran berasal dari pH basa NaOH. Penambahan 75 mLNaOH 0,1 M Bersisa basa kuat NaOH sebanyak 2,5mmol sehingga perhitungan pH campuran berasal dari pH basa NaOH. Jadi, pH campuran setelah penambahan NaOH 0,1 M secara berturut-turut adalah 8 + log 7, 11 + log 9, dan 12 + log 1,6.

Penentuan pH campuran sebagai berikut.

  • Penambahan 50 mL NaOH 0,1 M berarti jumlah mol asam lemah dan basa kuat tepat habis bereaksi sehingga terbentuk garam.

table attributes columnalign right center left columnspacing 0px end attributes row cell n space C H subscript 3 C O O Na end cell equals cell n space C H subscript 3 C O O H end cell row blank equals cell 5 space mmol end cell row cell open square brackets C H subscript 3 C O O Na close square brackets end cell equals cell fraction numerator n over denominator V space total end fraction end cell row blank equals cell fraction numerator 5 space mmol over denominator left parenthesis 50 plus 50 right parenthesis mL end fraction end cell row blank equals cell 5 cross times 10 to the power of negative sign 2 end exponent space M end cell row blank blank blank 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 C H subscript 3 C O O to the power of minus sign and H subscript 2 O end cell rightwards harpoon over leftwards harpoon cell C H subscript 3 C O O H and O H to the power of minus 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 open square brackets C H subscript 3 C O O Na close square brackets end root end cell row blank equals cell square root of fraction numerator 10 to the power of negative sign 14 end exponent space over denominator 10 to the power of negative sign 5 end exponent end fraction 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 space end root end cell row blank equals cell 7 cross times 10 to the power of negative sign 6 end exponent end cell 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 7 cross times 10 to the power of negative sign 6 end exponent end cell row blank equals cell 6 minus sign log space 7 end cell row pH equals cell 14 minus sign pOH end cell row blank equals cell 14 minus sign left parenthesis 6 minus sign log space 7 right parenthesis end cell row blank equals cell 8 plus log space 7 end cell end table  

  • Setelah ditambah 60 mL NaOH 0,1 M

table attributes columnalign right center left columnspacing 0px end attributes row cell n space C H subscript 3 C O O H end cell equals cell M cross times V end cell row blank equals cell 0 comma 1 cross times 50 end cell row blank equals cell 5 space mmol end cell row cell n space Na O H end cell equals cell M cross times V end cell row blank equals cell 0 comma 1 cross times 60 end cell row blank equals cell 6 space mmol end cell end table

  

Bersisa basa kuat NaOH sebanyak 1 mmol sehingga perhitungan pH campuran berasal dari pH basa NaOH.

table attributes columnalign right center left columnspacing 0px end attributes row cell open square brackets Na O H close square brackets end cell equals cell fraction numerator n over denominator V space total end fraction end cell row blank equals cell fraction numerator 1 space mmol over denominator 110 space mL end fraction end cell row blank equals cell 9 cross times 10 to the power of negative sign 3 end exponent end cell row cell Na O H end cell rightwards arrow cell Na to the power of plus sign and O H to the power of minus sign end cell row cell open square brackets O H to the power of minus sign close square brackets end cell equals cell b cross times M end cell row blank equals cell 1 cross times 9 cross times 10 to the power of negative sign 3 end exponent end cell row blank equals cell 9 cross times 10 to the power of negative sign 3 end exponent end cell 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 9 cross times 10 to the power of negative sign 3 end exponent end cell row blank equals cell 3 minus sign log space 9 end cell row pH equals cell 14 minus sign pOH end cell row blank equals cell 14 minus sign left parenthesis 3 minus sign log space 9 right parenthesis end cell row blank equals cell 11 plus log space 9 end cell end table 

  • Penambahan 75 mL NaOH 0,1 M

table attributes columnalign right center left columnspacing 0px end attributes row cell n space C H subscript 3 C O O H end cell equals cell M cross times V end cell row blank equals cell 0 comma 1 cross times 50 end cell row blank equals cell 5 space mmol end cell row cell n space Na O H end cell equals cell M cross times V end cell row blank equals cell 0 comma 1 cross times 75 end cell row blank equals cell 7 comma 5 space mmol end cell end table 

Bersisa basa kuat NaOH sebanyak 2,5 mmol sehingga perhitungan pH campuran berasal dari pH basa NaOH.

table attributes columnalign right center left columnspacing 0px end attributes row cell open square brackets Na O H close square brackets end cell equals cell fraction numerator n over denominator V space total end fraction end cell row blank equals cell fraction numerator 2 space mmol over denominator 125 space mL end fraction end cell row blank equals cell 1 comma 6 cross times 10 to the power of negative sign 2 end exponent end cell row cell Na O H end cell rightwards arrow cell Na to the power of plus sign and O H to the power of minus sign end cell row cell open square brackets O H to the power of minus sign close square brackets end cell equals cell b cross times M end cell row blank equals cell 1 cross times 1 comma 6 cross times 10 to the power of negative sign 2 end exponent end cell row blank equals cell 1 comma 6 cross times 10 to the power of negative sign 2 end exponent end cell 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 1 comma 6 cross times 10 to the power of negative sign 2 end exponent end cell row blank equals cell 2 minus sign log space 1 comma 6 end cell row pH equals cell 14 minus sign pOH end cell row blank equals cell 14 minus sign left parenthesis 2 minus sign log space 1 comma 6 right parenthesis end cell row blank equals cell 12 plus log space 1 comma 6 end cell end table 

Jadi, pH campuran setelah penambahan NaOH 0,1 M secara berturut-turut adalah 8 + log 7, 11 + log 9, dan 12 + log 1,6.

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