Transcript Precipitation PowerPoint

Chapter 6: Chemical Reactions
 Predict and write equations for
precipitation reactions.
 Write molecular, complete ionic, and
net ionic equations.
 Double displacement reactions occur
when ions exchange between two
compounds.
 A double-displacement reaction follows
the general form
 AB + CD  AD + BC
 Reactions that form a solid, called a
precipitate, upon mixing two aqueous
solutions are known as precipitation
reactions.
 Precipitation reactions do not always
occur when mixing two aqueous
solutions.
 The key to predicting precipitation
reactions is understanding that only
insoluble compounds form
precipitates.

Before mixing, KI(aq) and Pb(NO3)2(aq) are both
dissociated in their respective solutions.

The instant that
the solutions are
mixed, all four
ions are present.

In this case, KNO3
is soluble, but
PbI2 is insoluble.
Consequently,
PbI2 precipitates.

2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq)
1.
Write an equation for the precipitation reaction
that occurs (if any) when solutions of sodium
carbonate and copper(II) chloride are mixed.
2.
Combine the cation from one reactant with the
anion from the other. Make sure to write correct
(charge-neutral) formulas for the new ionic
compounds.
Na2CO3(aq) + CuCl2(aq) 
3.
Use the solubility rules to determine whether any
of the potential new products are indeed
insoluble.
Na2CO3(aq) + CuCl2(aq)  NaCl
+ CuCO3
4.
If all of the potentially insoluble products are
soluble, there will be no precipitate. Write NO
REACTION next to the arrow.
5.
One of the potentially insoluble products is
insoluble, so write its formula as the product of
the reaction, using (s) to indicate solid. Write the
soluble product with (aq) to indicate aqueous.
Na2CO3(aq) + CuCl2(aq)  NaCl(aq) + CuCO3(s)
6.
Balance the equation.
Na2CO3(aq) + CuCl2(aq)  NaCl(aq) + CuCO3(s)
Na2CO3(aq) + CuCl2(aq)  2NaCl(aq) + CuCO3(s)

Use the solubility rules to predict what will happen
when the following solutions are mixed. Write the
balanced equation for any reaction that occurs.
 Na2SO4(aq) and Pb(NO3)2(aq)
 KNO3 (aq) and BaCl2(aq)
 Potassium hydroxide(aq) and Iron (III) nitrate(aq)
 Ionic equations that show all of the
particles in a solution as they actually
exist are called complete ionic
equations.
 2NaOH(aq) + CuCl2(aq) → 2NaCl(aq) + Cu(OH)2(s)
 2Na+(aq) + 2OH–(aq) + Cu2+(aq) + 2Cl–(aq)
→ 2Na+(aq) + 2Cl–(aq) + Cu(OH)2(s)

Ions that do not participate in a reaction are
called spectator ions and are not usually
written in ionic equations.
 A reaction is only taking place if a solid, water, or
a gas is formed!
 Formulas that include only the particles
that participate in reactions are called
net ionic equations.
 2NaOH(aq) + CuCl2(aq) → 2NaCl(aq) + Cu(OH)2(s)

2Na+(aq) + 2OH–(aq) + Cu2+(aq) + 2Cl–(aq) →
2Na+(aq) + 2Cl–(aq) + Cu(OH)2(s)
 2OH–(aq) + Cu2+(aq) → Cu(OH)2(s)

Write chemical, complete ionic, and net
ionic equations for each of the following
reactions that produce a precipitate.
 Aqueous solutions of potassium iodide and
silver nitrate are mixed, forming the precipitate
silver iodide.
 Aqueous solutions of aluminum chloride and
sodium hydroxide are mixed, forming the
precipitate aluminum hydroxide.
 Aqueous solutions of sodium carbonate and
manganese (V) chloride are mixed.