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LOGO

Reaksi Pengendapan

A.S.

MINGGU KE 2

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REAKSI PENGENDAPAN

two or more soluble species

combine to form

an insoluble product (precipi tate )

Pb2+ (aq ) + 2Cl –

(aq ) PbCl2(s )

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CONTOH

• pengendapan mineral akibatpembentukan garam kalsium di organginjal

• pembekuan darah

Reaksi dalam tubuh manusia:

Timbulnya kerak pada alat untukpemanasan air dengan kesadahan tinggi

Proses sehari-hari :

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PbCl

2

NaCl

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NaOH

HCl

Mg OH)

2

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  Cl  Ag  AgCl 

K

sp

= Solubility Product Constants

 tetapan kesetimbangan/hasil kali kelarutan)

  Cl  Ag  Ksp

Jumlah maksimum zat yang

dapat larut dalam sejumlah

pelarut

V 

n s  

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Q < Ksp Tak Jenuh (≠ endapan)

Q = Ksp Jenuh

Q > Ksp Lewat Jenuh (endapan)

 s s s

CrO Ag CrO Ag  

2

42

42   2

Q = hasil kali konsentrasi ion-ion

  242CrO Ag  Ksp

  32

42   s s s Ksp 

PREDIKSI TERBENTUK ENDAPAN

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Calculate [HCl] required to precipitate AgCl

from 100 mL 0.1 M AgNO3? (Ksp = 1.8 x 10-10)

Solution consist of 0.10 M Ag+ and 0.10 M Pb2+

Ksp AgBr = 3.3 x 10-13

Ksp PbBr 2 = 6.4 x 10-6

Plan: Add Br - until all AgBr is precipitate, but no

PbBr 2 is precipitate. Calculate [Br -] required to

precipitate!

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100 mL of 0.1 M potassium sulfate solution is added

to a 100 mL solution of 0.2 M barium nitrate.

Calculate the mass of the precipitate formed and

the concentration of remaining ions in the solution!

A solution contains 0.020 M Ag+ and Pb2+.Add CrO4

2- to precipitate red Ag2CrO4 and

yellow PbCrO4. Which precipitates first?Data: Ksp Ag2CrO4 = 9.0 x 10

-12

Ksp PbCrO4 = 1.8 x 10-14

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PROBLEM 6

a. Will a precipitate form when 150 mL of 0.1 M Pb(NO3)2 are

combined with 100 mL of 0.2 M NaCl?

Ksp = 1.2 x 10-5

b. What minimum concentration of Na2CO3(aq) is required to causeprecipitation of BaCO3(s) from a solution of 1.0 x 10

-5M BaCl2(aq)?

Ksp = 2.6 x 10-9

c. What compound, if any, will precipitate when 80.0 mL of 1.0 x 10-5

MBa(OH)2(aq) is dded to 20mL 1.0 x 10

-5M Fe2(SO4)3?

)()()(   22   aqCl aq Pb s PbCl  

)()()(  2

3

2

3   aqCOaq Ba s BaCO 

102

4

2

4   101.1)()()( 

  KspaqSOaq Ba s BaSO

  393

3   106.2)()()( 

  KspaqOH aq Fe sOH  Fe