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Untuk membuat 500 mL larutan dengan pH=12, berapa gram yang diperlukan?

Untuk membuat 500 mL larutan begin mathsize 14px style Ca open parentheses O H close parentheses subscript 2 end style dengan pH=12, berapa gram begin mathsize 14px style Ca open parentheses O H close parentheses subscript 2 end style yang diperlukan? begin mathsize 14px style left parenthesis Ar space Ca equals 40 comma space O equals 16 comma space H equals 1 right parenthesis end stylespace

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Jawaban:

Larutan begin mathsize 14px style Ca open parentheses O H close parentheses subscript 2 end style merupakan basa, sehingga untuk perhitungan untuk mencari massa zat terlarut, pH diubah dahulu menjadi pOH.

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell pH and pOH end cell equals 14 row pOH equals cell 14 minus sign 12 end cell row pOH equals 2 end table end style 

Kemudian dicari konsentrasi undefined.

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes 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 2 equals cell negative sign log space open square brackets O H to the power of minus sign close square brackets end cell row cell open square brackets O H to the power of minus sign close square brackets end cell equals cell 10 to the power of negative sign 2 end exponent end cell end table end style 

begin mathsize 14px style Ca open parentheses O H close parentheses subscript 2 end style merupakan basa kuat, maka:

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 b cross times M subscript b end cell row cell 10 to the power of negative sign 2 end exponent end cell equals cell 2 cross times M subscript b end cell row cell M subscript b end cell equals cell 5 cross times 10 to the power of negative sign 3 end exponent end cell end table end style 

Setelah diperoleh konsentasi basa, maka dapat diperoleh massa zat terlarut. 

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell M subscript r space Ca open parentheses O H close parentheses subscript 2 end cell equals cell A subscript r space Ca plus 2 left parenthesis A subscript r space O and A subscript r space H right parenthesis end cell row blank equals cell 40 plus 2 left parenthesis 16 plus 1 right parenthesis end cell row blank equals cell 40 plus 34 end cell row blank equals 74 end table end style 

begin mathsize 14px style table attributes columnalign right center left columnspacing 0px end attributes row cell M subscript b end cell equals cell massa over M subscript r cross times 1000 over V end cell row cell 5 cross times 10 to the power of negative sign 3 end exponent end cell equals cell massa over 74 cross times 1000 over 500 end cell row massa equals cell 185 cross times 10 to the power of negative sign 3 end exponent space gram end cell end table end style 

Jadi, massa zat terlarutnya adalah 0,185 gram.

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