Solubility Lesson 6 Separating Ions

Positive ions react with negative ions to give a precipitate if they have low solubility . A precipitate can be separated from a solution by filtration . The precipitate will be on the filter paper while the soluble ions will go through. To separate ions one ion must be low solubility and all others high .

Separating Positive Ions

1.

Separate Ba 2+ &

Start at the top of page 4 and try Cl first

Pb 2+

Ba 2+ 1 st add Cl , it reacts with Pb 2+ ( low ) and not Ba 2+ ( high ) 2 nd add SO 4 2 , it reacts with Ba 2+ ( low )

Filter NaCl Na

+

Pb

2+

Ba

2+ PbCl 2

Cl

-

NO

3 -

Separating Positive Ions

1.

Separate Ba 2+ i.

Pb 2+

ii.

Ba 2+

Add

+

Add

+

& Pb 2+

NaCl 2Cl -

 Filter out

PbCl 2(s) PbCl 2(s) Na 2 SO 4

Filter out

BaSO 4(s) SO 4 2-



BaSO 4(s) Cl -

does not exist on its own Add

NaCl

because it is soluble- always use

Na +

for negative ions

Separating Positive Ions

2.

Separate Cu 2+ , Mg 2+ & Sr 2+

Cu 2+ Mg 2+ Sr 2+ Cu 2+ Mg 2+ Cu 2+ Mg 2+

Separating Positive Ions

2.

i.

ii.

iii.

Separate Cu 2+ , Mg 2+ & Sr 2+ Add

Sr 2+

Add

Cu 2+ Na 2 SO 4

Filter out

SrSO 4(s) + Na 2 S SO 4 2-



SrSO 4(s)

Filter out

CuS (s) + S 2-



CuS (s)

Add

Mg 2+ NaOH + 2OH -

Filter out

Mg(OH) 2(s)



Mg(OH) 2(s) SO 4 2-

does not exist on its own Add

Na 2 SO 4

because it is soluble- always use

Na +

for negative ions

Separating Negative Ions

Remove the

lowest negative ion

on the chart first by adding a

positive cation

.

3.

Separate Cl & OH Look for a

cation

that is low with

OH (lowest)

and

high

with

Cl .

Ba 2+ Ba 2+

Look for a

cation

that is low with with

Cl -

Look for a

cation

that is low with

OH (lowest)

and

high

with

Cl .

Remove the

lowest negative ion

first by adding a

positive cation

.

Separating Negative Ions

3.

i.

ii.

Separate Cl & OH -

Ba 2+

works so add

Ba(NO 3 ) 2

and filter out

Ba(OH) 2(s) Ba 2+ + 2OH -



Ba(OH) 2(s)

Add

Ag +

as

AgNO 3

and filter out

AgCl (s) Ba 2+

does not exist on its own Add

Ba(NO 3 ) 2

because it is soluble- always use

NO 3 -

to pair with positive ions

Ag + + Cl -



AgCl (s)

Separating Negative Ions

4.

Separate Cl S 2 CO 3 2-

Zn 2+ Ba 2+

Look for a

cation

that is low with with

Cl -

Look for a

cation

that is low with

S 2-

and high with

Cl -

Look for a

cation

that is

low

with

CO 2-

and

high

with

Cl and S 2-

Separating Negative Ions

4.

i.

ii.

Separate Cl S 2 CO 3 2-

Ba 2+

works so add

Ba(NO 3 ) 2

and filter out

BaCO 3(s) Ba 2+ + CO 3 2-



BaCO 3(s)

Add

Zn 2+ Zn 2+ +

as

Zn(NO 3 ) 2

and filter out

ZnS (s) S 2-



ZnS (s) Ba 2+

does not exist on its own Add

Ba(NO 3 ) 2

because it is soluble- always use

NO 3 -

to pair with positive ions

iii.

Add

Ag +

as

AgNO 3

and filter out

AgCl

(s )

Ag + + Cl -



AgCl (s)