Precipitation Reactions - MTH · 2019-10-09 · Then determine if each new product is soluble (aq) or insoluble (s)! Don’t forget to balancethe chemical reaction! 1NiCl 2(aq) +

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

Precipitation ReactionsDR. MIOY T. HUYNHYALE UNIVERSITYCHEMISTRY 161

FALL 2019

www.mioy.org/chem161

http://www.mioy.org/chem161


What is a salt?A salt is an ionic compound: metal + nonmetal

Some salts are soluble in water (aqueous, aq = dissolves in water).Some salts are insoluble in water (precipitate, solid, s).

Q: What happens when we mix salt solutions?

A: Sometimes we can get a new, insoluble salt

(or a precipitate) to form.

Sometimes nothing happens though …

It really depends on the ions.

Exceptions

SOLU

BLE

Group 1 cations

NH4+

NO3–

CH3COO–

Cl–, Br–, I– Ag+, Hg22+, Pb2+, Cu+

SO42– Hg2

2+, Pb2+, Ba2+, Ca2+, Sr2+,

INSO

LUB

LE OH– Group 1 cations, Ba2+, Ca2+, Sr2+, NH4+

S2– Group 1 cations, Ba2+, Ca2+, Sr2+, NH4+

CO32–, PO4

3–, F– Group 1 cations, NH4+


Example

Say we mix an aqueous solution of nickel(II) chloride with an aqueous solution of sodium sulfide.


Example


We can write the reactants of this chemical reaction:NiCl2 (aq) + Na2S (aq) →


Example



We can predict the products by exchanging the ions (we call these double exchange reactions):NiCl2 (aq) + Na2S (aq) →


Example



We can predict the products by exchanging the ions (we call these double exchange reactions):NiCl2 (aq) + Na2S (aq) → NiS (s)


Example



We can predict the products by exchanging the ions (we call these double exchange reactions):NiCl2 (aq) + Na2S (aq) → NiS (s) + NaCl (aq)


Example




Determine the products first. Then determine if each new product is soluble (aq) or insoluble (s)!


Example




Determine the products first. Then determine if each new product is soluble (aq) or insoluble (s)!


Example




Determine the products first. Then determine if each new product is soluble (aq) or insoluble (s)!Don’t forget to balance the chemical reaction!

1NiCl2 (aq) + 1Na2S (aq) → 1NiS (s) + 2NaCl (aq)


Example






Always go back to the microscopic picture of what’s happening!

Ni2+

Na+

Cl–

Cl– Na+

S2–


Example






Always go back to the microscopic picture of what’s happening!→ NiS precipitate (solid) forms & other ions float in solution

Na+

Cl–

Cl–

Na+

NiS (s)

Ni2+

Na+

Cl–

Cl– Na+

S2–


Writing Chemical Equations

This is called a molecular equation because we keep the salt as neutral “molecules”:1NiCl2 (aq) + 1Na2S (aq) → 1NiS (s) + 2NaCl (aq)



But we know that soluble salts (aqueous solutions) exist as dissociated ions!It would be more accurate to dissociate the soluble salts.






We can transform the molecular equation into an complete ionic equation:1Ni+ (aq) + 2Cl– (aq) + 2Na+ (aq) + 1S2– (aq) → 1NiS (s) + 2Na+ (aq) + Cl– (aq)

Na+

Cl–

Cl–

Na+

NiS (s)

Ni2+

Na+

Cl–

Cl– Na+

S2–






Na+

Cl–

Cl–

Na+

NiS (s)

Ni2+

Na+

Cl–

Cl– Na+

S2–

SPECTACTOR IONSYou may notice that some ofthese ions (Na+ and Cl–) don’tactually chemically react.

We can ignore these!






We can write a net ionic equation by eliminating all the spectator ions:

Na+

Cl–

Cl–

Na+

NiS (s)

Ni2+

Na+

Cl–

Cl– Na+

S2–








We can write a net ionic equation by eliminating all the spectator ions: 1Ni+ (aq) + 1S2– (aq) → 1NiS (s)

Na+

Cl–

Cl–

Na+

NiS (s)

Ni2+

Na+

Cl–

Cl– Na+

S2–




Predicting Products of a Precipitation Reaction

When we mix to aqueous salt solutions together, we can sometimes get a new precipitate to form:1NiCl2 (aq) + 1Na2S (aq) → 1NiS (s) + 2NaCl (aq)

We call these double exchange reactions because we “swap” the two ions (red and blue).

We are able to predict the products because we know that the products are also salts, which are neutral.






It’s important that you practice assigning charges to the ions before you take the shortcut of swapping the ions. To help, I like to imagine a chart like this:







Ni2+ Na+

Cl– NiCl2 NaCl (aq)S2– NiS (s) Na2S







Ni2+ Na+


Using a chart like this helps you get comfortablepredicting the products because the charges arewritten out explicitly.







Ni2+ Na+


Using a chart like this helps you get comfortablepredicting the products because the charges arewritten out explicitly.Once you do enough of these problems, you cantake the shortcut of “swapping” the ions like above.


Write the molecular equation for each of the following reactions:

1. A nickel(II) chloride solution is mixed with an ammonium sulfate solution.

2. An aqueous solution of potassium carbonate is added to a barium nitrate solution.

3. FeSO4 (aq) + KOH (aq) →

4. CaBr2 (aq) + NaCl (aq) →



1. A nickel(II) chloride solution is mixed with an ammonium sulfate solution.




In a molecular equation: keep everything as a neutral “molecule”



1. A nickel(II) chloride solution is mixed with an ammonium sulfate solution. NiCl2 (aq) + (NH4)2SO4 (aq) →




Ni2+ NH4+

Cl–

SO42–




1. A nickel(II) chloride solution is mixed with an ammonium sulfate solution. NiCl2 (aq) + (NH4)2SO4 (aq) → NiSO4 (aq) + 2NH4Cl (aq)




Ni2+ NH4+

Cl– NH4Cl (aq)SO42– NiSO4 (aq)








Ni2+ NH4+


Remember to balance the equation!




2. An aqueous solution of potassium carbonate is added to a barium nitrate solution.K2CO3 (aq) + Ba(NO3)2 (aq) →



Ni2+ NH4+


K+ Ba2+

CO32–

NO3–




2. An aqueous solution of potassium carbonate is added to a barium nitrate solution.K2CO3 (aq) + Ba(NO3)2 (aq) → 2KNO3 (aq) + BaCO3 (s)



Ni2+ NH4+


K+ Ba2+

CO32– BaCO3 (s)NO3– KNO3 (aq)







Ni2+ NH4+


K+ Ba2+








Ni2+ NH4+


K+ Ba2+


Fe2+ K+

SO42–

OH–





3. FeSO4 (aq) + 2KOH (aq) → Fe(OH)2 (s) + K2SO4 (aq)


Ni2+ NH4+


K+ Ba2+


Fe2+ K+

SO42– K2SO4 (aq)OH– Fe(OH)2 (s)







Ni2+ NH4+


K+ Ba2+


Fe2+ K+








Ni2+ NH4+


K+ Ba2+


Fe2+ K+


Ca2+ Na+

Br–

Cl–







Ni2+ NH4+


K+ Ba2+


Fe2+ K+


Ca2+ Na+

Br– NaBr (aq)Cl– CaCl2 (aq)






4. CaBr2 (aq) + 2NaCl (aq) → CaCl2 (aq) + 2NaBr (aq)

Ni2+ NH4+


K+ Ba2+


Fe2+ K+


Ca2+ Na+








Ni2+ NH4+


K+ Ba2+


Fe2+ K+


Ca2+ Na+



Write the complete ionic equation for each of the following reactions:











In a complete ionic equation: write the soluble or aqueous (aq) “molecules” as dissociated ions



1. A nickel(II) chloride solution is mixed with an ammonium sulfate solution. NiCl2 (aq) + (NH4)2SO4 (aq) → NiSO4 (aq) + 2NH4Cl (aq)Ni2+ (aq) + 2Cl– (aq) + 2NH4+ (aq) + SO42– (aq) → Ni2+ (aq) + SO42– (aq) + 2NH4+ (aq)+ 2Cl– (aq)




In a complete ionic equation: write the soluble or aqueous (aq) “molecules” as dissociated ions







Remember to balance your equation!




2. An aqueous solution of potassium carbonate is added to a barium nitrate solution.K2CO3 (aq) + Ba(NO3)2 (aq) → 2KNO3 (aq) + BaCO3 (s)2K+ (aq) + CO32– (aq) + Ba2+ (aq) + 2NO3– (aq) → 2K+ (aq) + 2NO3– (aq) + BaCO3 (s)













3. FeSO4 (aq) + 2KOH (aq) → Fe(OH)2 (s) + K2SO4 (aq)Fe2+ (aq) + SO42– (aq) + 2K+ (aq) + 2OH– (aq) → Fe(OH)2 (s) + 2K+ (aq) + SO42– (aq)













4. CaBr2 (aq) + 2NaCl (aq) → CaCl2 (aq) + 2NaBr (aq)Ca2+ (aq) + 2Br– (aq) + 2Na+ (aq) + 2Cl– (aq) → Ca2+ (aq) + 2Cl– (aq) + 2Na+ (aq)+ 2Br– (aq)








Write the net ionic equation for each of the following reactions:











In a net ionic equation: get rid of the “spectator ions” and only keep what forms the precipitate or insoluble salt (s)










1. A nickel(II) chloride solution is mixed with an ammonium sulfate solution. NiCl2 (aq) + (NH4)2SO4 (aq) → NiSO4 (aq) + 2NH4Cl (aq)Ni2+ (aq) + 2Cl– (aq) + 2NH4+ (aq) + SO42– (aq) → Ni2+ (aq) + SO42– (aq) + 2NH4+ (aq)+ 2Cl– (aq) → This reaction doesn’t form any precipitate, so no net ionic equation!















2. An aqueous solution of potassium carbonate is added to a barium nitrate solution.K2CO3 (aq) + Ba(NO3)2 (aq) → 2KNO3 (aq) + BaCO3 (s)2K+ (aq) + CO32– (aq) + Ba2+ (aq) + 2NO3– (aq) → 2K+ (aq) + 2NO3– (aq) + BaCO3 (s) CO32– (aq) + Ba2+ (aq) + → BaCO3 (s)















3. FeSO4 (aq) + 2KOH (aq) → Fe(OH)2 (s) + K2SO4 (aq)Fe2+ (aq) + SO42– (aq) + 2K+ (aq) + 2OH– (aq) → Fe(OH)2 (s) + 2K+ (aq) + SO42– (aq)Fe2+ (aq) + 2OH– (aq) → Fe(OH)2 (s)









Remember to balance your equation!






4. CaBr2 (aq) + 2NaCl (aq) → CaCl2 (aq) + 2NaBr (aq)Ca2+ (aq) + 2Br– (aq) + 2Na+ (aq) + 2Cl– (aq) → Ca2+ (aq) + 2Cl– (aq) + 2Na+ (aq)+ 2Br– (aq)→ This reaction doesn’t form any precipitate, so no net ionic equation!

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Precipitation Reactions - MTH · 2019-10-09 · Then determine if each new product is soluble (aq) or insoluble (s)! Don’t forget to balancethe chemical reaction! 1NiCl 2(aq) +