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Sebanyak 3,12 gram basa lemah  dilarutkan ke dalam...

Sebanyak 3,12 gram basa lemah begin mathsize 14px style italic L open parentheses O H close parentheses subscript 3 end style dilarutkan ke dalam 200 mL larutan begin mathsize 14px style italic L Cl subscript 3 end style 0,2 M menghasilkan larutan penyangga dengan pH = 9. Jika begin mathsize 14px style K subscript b space italic L open parentheses O H close parentheses subscript 3 equals 10 to the power of negative sign 5 end exponent end style, massa atom relatif unsur L adalah .... (begin mathsize 14px style A subscript r colon space H equals 1 space g space mol to the power of negative sign 1 end exponent space dan space O equals 16 space g space mol to the power of negative sign 1 end exponent end style)space 

Jawaban:

Massa atom relatif L dapat dicari dengan mencari mol basa lemah dengan larutan penyangga basa dengan pH=9.


begin mathsize 14px style pH equals 9 pOH equals 14 minus sign 9 equals 5 open square brackets O H to the power of minus sign close square brackets equals 10 to the power of negative sign 5 end exponent  open square brackets O H to the power of minus sign close square brackets double bond K subscript b cross times fraction numerator mol space basa over denominator mol space garam end fraction 10 to the power of negative sign 5 end exponent equals 10 to the power of negative sign 5 end exponent cross times fraction numerator mol space basa over denominator 0 comma 2 space M space. space 200 cross times 10 to the power of negative sign 3 end exponent space L space end fraction mol space basa equals 0 comma 2 space M point 200 cross times 10 to the power of negative sign 3 end exponent L mol space basa equals 0 comma 04 space mol end style 
 

Setelah mol basa diketahui, massa atom relatif L dapat diketahui melalui cara berikut ini;
 

begin mathsize 14px style Mol space italic L open parentheses O H close parentheses subscript 3 equals fraction numerator massa over denominator Mr end fraction Mr space italic L open parentheses O H close parentheses subscript 3 equals fraction numerator massa over denominator mol end fraction Ar space L plus left parenthesis 3 cross times left parenthesis Ar space O plus space Ar space H right parenthesis right parenthesis equals massa over mol Ar space L plus left parenthesis 3 cross times left parenthesis 16 plus 1 right parenthesis right parenthesis equals fraction numerator 3 comma 12 space gram over denominator 0 comma 04 space mol end fraction Ar space L plus 51 equals 78 space begin inline style bevelled g over mol end style Ar space L equals 78 minus sign 51 space begin inline style bevelled g over mol end style Ar space L equals 27 space begin inline style bevelled g over mol end style end style 
 

Jadi, massa atom relatif (Ar) L adalah 27 g/mol.space 

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