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Direaksikan 250 mL larutan  0,2 M dengan 250 mL la...

Direaksikan 250 mL larutan begin mathsize 14px style N H subscript 3 end style 0,2 M dengan 250 mL larutan HCI 0,2 M. (Kb begin mathsize 14px style N H subscript 3 end style(aq) = 1,8 x 10-5)

a. Tentukan pH larutan sebelum bereaksi!
b. Tentukan pH larutan setelah bereaksi!

 

Jawaban:

a. pH sebelum reaksi
begin mathsize 14px style N H subscript 3 space merupakan space basa space lemah V space equals space 250 space mL space equals space 0 comma 25 space L M space equals space 0 comma 2 space M open square brackets O H to the power of minus sign close square brackets space equals space square root of K subscript b space x space M subscript b end root open square brackets O H to the power of minus sign close square brackets space equals space square root of 1 comma 8 space x space 10 to the power of negative sign 5 end exponent space x space 0 comma 2 end root open square brackets O H to the power of minus sign close square brackets space equals space square root of 3 comma 6 space x space 10 to the power of negative sign 6 end exponent end root open square brackets O H to the power of minus sign close square brackets space equals space 1 comma 897 space x space 10 to the power of negative sign 3 end exponent pOH space equals space minus sign space log space open square brackets O H to the power of minus sign close square brackets pOH space equals space minus sign space log space 1 comma 897 space x space 10 to the power of negative sign 3 end exponent pOH space equals space 3 space minus sign space log space 1 comma 897  pH space equals space 14 space minus sign space pOH pH space equals space 14 space minus sign space left parenthesis 3 minus sign log space 1 comma 897 right parenthesis pH space equals space 11 plus log space 1 comma 897 pH space equals space 11 comma 278 end style  

begin mathsize 14px style H Cl space merupakan space asam space kuat V space H Cl space equals space 250 space mL space equals space 0 comma 25 space L M space H Cl space equals space 0 comma 2 space M open square brackets H to the power of plus sign close square brackets space equals space Ma space x space a open square brackets H to the power of plus sign close square brackets space equals 0 comma 2 space M space x space 1 open square brackets H to the power of plus sign close square brackets space equals space 0 comma 2 space M pH space equals space minus sign space log space open square brackets H to the power of plus sign close square brackets pH space equals space minus sign space log space 2 space x space 10 to the power of negative sign 1 end exponent pH space equals space 1 space minus sign space log space 2 pH space equals space 0 comma 699 end style   
 

b. pH larutan setelah bereaksi

begin mathsize 14px style mol space Basa space equals space M space x space V mol space Basa space equals space 0 comma 2 space M space x space 0 comma 25 space L mol space Basa space equals space 0 comma 05 space mol  mol space Asam space equals space M space x space V mol space Asam space equals space 0 comma 2 space space 0 comma 25 mol space Asam space equals space 0 comma 05 space mol end style 

Persamaan reaksinya adalah:

 

Pereaksi habis tak bersisa, maka termasuk hidrolisis, garam yang terbentuk adalah garam asam karena berasal dari asam kuat dan basa lemah

Mencari pH garam asam:

begin mathsize 14px style open square brackets H to the power of plus sign close square brackets space equals space space square root of K subscript w over K subscript b x space M end root open square brackets H to the power of plus sign close square brackets space equals space space square root of K subscript w over K subscript b x space n over V end root open square brackets H to the power of plus sign close square brackets space equals space space square root of fraction numerator 10 to the power of 14 over denominator 1 comma 8 space x space 10 to the power of negative sign 5 end exponent end fraction x space fraction numerator 0 comma 05 space mol over denominator 0 comma 5 space L end fraction end root open square brackets H to the power of plus sign close square brackets space equals space space square root of fraction numerator 10 to the power of negative sign 14 end exponent over denominator 1 comma 8 space x space 10 to the power of negative sign 5 end exponent end fraction x space fraction numerator 0 comma 05 space mol over denominator 0 comma 5 space L end fraction end root open square brackets H to the power of plus sign close square brackets space equals space space square root of 5 comma 556 space x space 10 to the power of negative sign 11 end exponent end root open square brackets H to the power of plus sign close square brackets space equals space 7 comma 45 space x space 10 to the power of negative sign 6 end exponent pH space equals space minus sign space log space open square brackets H to the power of plus sign close square brackets pH space equals space minus sign space log space 7 comma 45 space x space 10 to the power of negative sign 6 end exponent pH space equals space 6 space minus sign space log space 7 comma 45 pH space equals space 6 space minus sign 0 comma 872 pH space equals space 5 comma 128 end style 

Jadi, pH basa lemah sebelum bereaksi adalah 11,278, pH asam kuat sebelum bereaksi adalah 0,699 dan pH setelah reaksi adalah 5,128.

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