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Berapa gram amonia  0,25 M, pH-nya 11 + log 2 dire...

Berapa gram amonia begin mathsize 14px style open parentheses N H subscript 3 close parentheses end style 0,25 M, pH-nya 11 + log 2 direaksikan dengan larutan asam formiat begin mathsize 14px style open parentheses H C O O H close parentheses end style 0,09 M yang pH-nya 3 - log 6. Hitunglah harga pH larutan 0,15 M garam begin mathsize 14px style H C O O N H subscript 4 end style yang terbentuk!

Jawaban:

Garam tersebut merupakan garam yang dibentuk dari basa lemah dan asam lemah. Maka dalam air, garam ini akan terhidrolisis total. Komponen sisa basa lemah akan bereaksi dengan air melepaskan ion begin mathsize 14px style H to the power of plus sign end style. Begitu pula sisa asam lemah akan bereaksi dengan air melepaskan ion begin mathsize 14px style O H to the power of minus sign end style. Sifat garam ini tergantung dari nilai begin mathsize 14px style K subscript a end style dan begin mathsize 14px style K subscript b end style masing-masing. Pada soal, nilai tersebut belum ada, namun kita dapat cari dari pH yang diketahui melalui perhitungan pH basa lemah

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell pH space N H subscript 3 end cell equals cell 11 plus log space 2 end cell row pOH equals cell 14 minus sign left parenthesis 11 plus log space 2 right parenthesis end cell row pOH equals cell 3 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 3 end exponent 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 b cross times M subscript b 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 b cross times 0 comma 25 end root space left parenthesis kuadratkan space kedua space ruas right parenthesis end cell row cell 4 cross times 10 to the power of negative sign 6 end exponent end cell equals cell K subscript b cross times 0 comma 25 end cell row cell K subscript b end cell equals cell 16 cross times 10 to the power of negative sign 6 end exponent end cell row blank equals cell 1 comma 6 cross times 10 to the power of negative sign 5 end exponent end cell end table end style 

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell pH space H C O O H end cell equals cell 3 minus sign log space 6 end cell row cell open square brackets H to the power of plus sign close square brackets end cell equals cell 6 cross times 10 to the power of negative sign 3 end exponent end cell 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 subscript a end root end cell row cell 6 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 09 end root space left parenthesis kuadratkan space kedua space ruas right parenthesis end cell row cell 36 cross times 10 to the power of negative sign 6 end exponent end cell equals cell K subscript a cross times 0 comma 09 end cell row cell K subscript a end cell equals cell 4 cross times 10 to the power of negative sign 4 end exponent end cell end table end style 

Perhatikan bahwa nilai begin mathsize 14px style K subscript a end style > begin mathsize 14px style K subscript b end style, maka sifat garam ini adalah asam, untuk menentukan pH:

begin mathsize 14px style 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 w over K subscript b cross times K subscript a end root end cell row blank equals cell square root of fraction numerator 10 to the power of negative sign 14 end exponent over denominator 1 comma 6 cross times 10 to the power of negative sign 5 end exponent end fraction cross times 4 cross times 10 to the power of negative sign 4 end exponent end root end cell row blank equals cell square root of 2 comma 5 cross times 10 to the power of negative sign 13 end exponent end root end cell row blank equals cell square root of 25 cross times 10 to the power of negative sign 14 end exponent end root end cell row blank equals cell 5 cross times 10 to the power of negative sign 7 end exponent end cell row pH equals cell negative sign log space 5 cross times 10 to the power of negative sign 7 end exponent end cell row pH equals cell 7 minus sign log space 5 end cell end table end style 

Jadi, pH campuran tersebut adalah 7 - log 5 atau sekitar 6,301.

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