precipitation rxns solubility, stoichiometry, and net ionic equations

Precipitation Rxns

Solubility, Stoichiometry, and

Net Ionic Equations

Precipitation Rxns: One Kind of Double Replacement (Metathesis) Rxn

Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)yellow solid

What Happens on the ‘Nanoscale’?

Draw a picture of what is present in Pb(NO3)2(aq) and KI(aq) before mixing.

Draw a picture of what is present after mixing.

Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)yellow solid

What Cation-Anion Combinations Precipitate?

Identify the cation and anion present in each solution before mixing.

After mixing, look for evidence that certain cations/anions tend to ppt

(Investigate This #2.32)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Results of 2.32 Mixing Tests

Which combinations result in pptn?

Which do not?

Categorize tendency of each cation and each anion to ppt



KNO3 KBr K2SO4 K2CO3 K2C2O4 K3PO4

NaCl

CaCl2

LiCl

BaCl2

Solubility Rules

From Your Text (p.100-101)

Appendix G of the Lab Manual (more extensive list)

CoCl2.6H2O and Na3PO4 Solutions (Investigate This 2.38)

Na3PO4(aq) contains colorless Na+(aq) and colorless PO4

3-(aq)



CoCl2.6H2O(aq) contains pink Co2+

(aq) and colorless Cl-(aq)

If the Solutions in 2.38 Are Mixed …

mix

blue solid forms

centrifuge

What products form? Na3PO4(aq) + CoCl2(aq) ?


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When Rxn Is Complete

Supernatant contains only Na+(aq) and Cl-(aq)

Blue ppt of Co3(PO4)2 is present

2Na3PO4(aq) + 3CoCl2(aq) Co3(PO4)2 (s) + 6NaCl(aq)

Three Ways to Write Eqn for 2.38

Whole formula equation

Ionic equation

Net ionic equation (excludes spectator ions)3Co2+(aq) + 2PO4

3-(aq) Co3(PO4)2(s)

2Na3PO4(aq) + 3CoCl2(aq) Co3(PO4)2 (s) + 6NaCl(aq)

6Na+(aq) + 2PO43-(aq) + 3Co2+(aq) + 6Cl-(aq)

Co3(PO4)2 (s) + 6Na+(aq) + 6Cl-(aq)

The Experiment in 2.38

3Co2+(aq) + 2PO43-(aq) Co3(PO4)2(s)



add Na3PO4 (aq)

CoCl2.6H2O(aq)

mix

centrifuge

blue solid forms







The Experiment in 2.38

3Co2+(aq) + 2PO43-(aq) Co3(PO4)2(s)

Do This For ONE Assigned Tube:

See table on the worksheet for information about M and V for the reactant solutions

Determine the number of moles of each reactant moles = M*V

Stoichiometry Calculations (2.38)



0.00090 mole 0.00045 mole Co2+

0.00090mole

0.00045 mole

0.00045 mole PO4

3-

Do This For Assigned Tube:

Identify which reactant will be consumed entirely (limiting reactant) and which will be in excess

Calculate the amount of each reactant left after rxn

Calculate the yield in moles

of Co3(PO4)2



0.00090 mole

More Stoichiometry Calculations (2.38)

Reaction Stoichiometry Results

Tube Co2+ excess or completely consumed?

PO43- excess or

completely consumed?

Moles Co2+ left at end

Moles PO43-

left at endMoles of Co3(PO4)2

1 consumed excess 0 0.00030 0.00030

2 excess consumed 0.00022 0 0.00023



3Co2+(aq) + 2PO4

3-(aq) Co3(PO4)2(s)

Why is supernatant in tube #2 pink?

Why are supernatants in other tubes colorless?

Why is the amount of blue ppt not the same in all the tubes?



Final Questions About 2.38

precipitation rxns solubility, stoichiometry, and net ionic equations

Documents

aq cocl

aq cocl

mole po

colorless na aq

colorless po

aq yellow solid slide

aq blue ppt

end moles po