Pick up a Packet and write down the following Essential Question: How are precipitation reactions written and how is a compound determined to be soluble or insoluble?

Precipitation Reactions (Reactions that form a precipitate)

Definition: Precipitate: A solid that forms as the result of a chemical reaction in aqueous solution.

Let’s see what this looks like: Click here for a video of a precipitation reactions in sodium carbonate. Click here for a video of a precipitation reactions in sodium carbonate. Click here for a video of a precipitation reaction. Click here for a video of a precipitation reaction

Precipitation Reaction: A reaction in which a solid is formed from a solution is called a precipitation reaction Solution = (aq) = soluble Soluble: it DOES dissolve Precipitate = (s) = insoluble Insoluble: it DOES NOT dissolve Reactants = 2 solutions (aq)  Products = 1 solution (aq) and 1 solid (s) If the products aren’t (aq) and (s) then no rxn occured What is the precipitate in the reaction below? Pb(NO 3 ) 2 (aq) + 2NaI (aq) PbI 2 (s) + 2NaNO 3 (aq)

First Step: Practice Using Solubility Rules – Are These Compounds Soluble or Insoluble in Water? 1. Barium Nitrate 2. Potassium Carbonate 3. Sodium Sulfate 4. Copper (II) Hydroxide 5. Mercury (I) Chloride 6. Ammonium Phosphate 7. Chromium (III) Sulfide 8. Lead (II) Sulfate

Solubility – Why does it matter? A precipitation reaction only occurs if one of the products is insoluble.

What Happens When an Ionic Compound Dissolves in Water? NaCl (s) NaCl (aq) But what does NaCl (aq) mean? NaCl particles in water ? dissolve Na and Cl atoms in water? separate Na + and Cl - ions in water ? Formed after they dissolve

When an ionic compound dissolves in water, it breaks apart into ions: NaCl (aq)  Na+ + Cl-

What would happen if solutions of NaCl and KBr were mixed? Now lets discuss how to predict the products of mixed solutions

Predicting whether a reaction happens What happens when solutions of BaCl 2 and Na 2 SO 4 are made? The ionic compounds break up into their cations and anions: BaCl 2 becomes Ba 2+ and Cl - Na 2 SO 4 becomes Na + and SO 4 2-

When the two solutions are mixed together, there will be 4 ions floating around: Ba 2+ Cl - Na + SO 4 2- A reaction will occur in this case because when the ions switch partners, there is the formation of a precipitate: BaCl 2 (aq) + Na 2 SO 4 (aq) BaSO 4 (s) + NaCl(aq) This is known as a double replacement rxn. How do we know the it was the barium sulfate that was the precipitate?? From the solubility rules!

Another example: Will a reaction occur between solutions of NaCl and AgNO 3 ? NaCl (aq) + AgNO 3 (aq)  ? The reactants separate into ions, so the ions could switch partners.

Using the solubility rules, we see that NaNO 3 is soluble, so those ions will continue to float around in the water. However, AgCl is insoluble:

Because we got a new substance (AgCl), a chemical reaction took place: NaCl (aq) + AgNO 3 (aq)  NaNO 3 (aq) + AgCl (s)

Steps for writing a precipitation reaction Step 1: Identify the reactants Step 2: Split each reactant into its positive and negative ions. Step 3: Identify the possible products of the reactants by swapping the positive and negative ions of the reactants. Step 4: Write the equation and balance it so that equal numbers of all atoms occur on both sides. Step 5: Use the Solubility Rules to find if one product is insoluble. If one product is insoluble, the reaction occurs. If both products are soluble, no reaction occurs.

Practice: Switch the partner ions and write balanced equations for each possible reaction. Use your Solubility Rules to see whether a precipitate forms. NaOH + CaCl 2 CuBr 2 + (NH 4 ) 2 CO 3 K 2 SO 4 + Fe(NO 3 ) 3

Net Ionic Equations Remove any spectator ions Ions present on both the reactant and product side of the equation. Solids and pure liquids must remain in the net ionic equations. Lets practice with the previous rxns: NaOH + CaCl 2 CuBr 2 + (NH 4 ) 2 CO 3 K 2 SO 4 + Fe(NO 3 ) 3

Recap….. Single Replacement Reactions Using the Activity series

Activity Series A chart of metals listed in order of declining relative reactivity. The top metals are more reactive than the metals on the bottom. The Halogens decrease in reactivity down the column.

Single replacement One element replaces a second element in a compound. the more reactive metal will replace the least reactive metal. the more reactive nonmetal will replace the least reactive nonmetal. General equation: A + BX → AX + B EX. 2AgNO 3 (aq) + Cu(s) → 2Ag(s) + Cu(NO3) 2 (aq) Silver nitrate reacts with copper to produce silver and copper

Let’s Practice… 1. Au + AgNO 3 → 2. Fe + Cu(NO 3 ) 2 → 3. Ca + H 2 O →

More Practice… 1. Zn + HCl → 2. K + NaCl → 3. Al + KI →