Double-Replacement Reactions

Metals donate or lose electrons when they become ions. + 2 Metals donate or lose electrons when they become ions. Beryllium This gives metals a positive charge. Positively charged ions are called cations. + 1 When elements lose electrons and increase their charge, we say that they have been oxidized. Sodium

Nonmetals gain or accept electrons when they become ions. - 2 Nonmetals gain or accept electrons when they become ions. This gives nonmetals a negative charge. Negatively charged ions are called anions. Oxygen - 1 When elements gain electrons and lower their charge, we say that they have been reduced. Chlorine

Oxidation and reduction never happen alone Oxidation and reduction never happen alone. In order for an element to donate electrons, there must be an element to accept those electrons. +1 -1 sodium sodium chloride chlorine

There are some reactions that occur that are NOT oxidation-reduction (redox) reactions. These reactions occur when ions rearrange themselves to form a solid or liquid product. Pb(NO3)2 (aq) + 2KI (aq) 2KNO3 (aq) + PbI2 (s)

Electrons are not being gained or lost, ions are just rearranging themselves. Ag NO3 Na Cl Because these reactions are basically just two ions changing places, these reactions are generally known as Double Displacement Reactions There are 2 specific types of double displacement reactions you will be asked to identify. The good news is that you have already learned them both!

Double Displacement Reaction: Precipitation Reaction A precipitation reaction occurs when aqueous solutions are mixed, and a reaction occurs which forms a solid product. (This solid product is known as the precipitate.) Pb(NO3)2 (aq) + 2KI (aq) 2KNO3 (aq) + PbI2 (s)

Double Displacement Reaction: Precipitation Reaction Notice the reactants [Pb(NO3)2 and KI] are both soluble. Inside each bottle of reactant, there are ions floating around in the solution. This is because ionic compounds break apart into ions when they are dissolved.

Double Displacement Reaction: Precipitation Reaction When the solutions are mixed, the ions from each solution are free to meet. Some ions come together that form an insoluble, solid compound. This is known as a precipitate and it falls to the bottom of the test tube. PbI2 is an insoluble solid.

Double Displacement Reaction: Precipitation Reaction There will also be a product that is soluble and still dissolved in the solution. These ions will remain dissolved in the water, and they are called spectator ions. KNO3 is soluble and still dissolved in the water.

7 H+ + OH-  H2O Double Displacement Reaction: Acid-Base Neutralization Reaction When an acid reacts with a base, the hydrogen ion (H+) is neutralized by a hydroxide ion (OH-) H+ + OH-  H2O This produces WATER! Remember, water has a neutral pH. What pH is this? 7

Double Displacement Reaction: Acid-Base Neutralization Reaction When an acid neutralizes a base, the metal from the base and the nonmetal from the acid also form a salt. HCl + NaOH  H2O + NaCl This salt is the created when the metal found in the base combines with the nonmetal or polyatomic ion found in the original acid.

Pb (NO3)2 Ca Cl2 H Br Li OH = H2O Notice that during a precipitation reaction, two aqueous reactants produce a solid product which is known as the precipitate. Pb (NO3)2 Ca Cl2 aqueous solid aqueous During an acid-base neutralization reaction, two aqueous reactants (an acid and a base) produce a liquid product which is simply known as the water! H Br Li OH = H2O aqueous aqueous liquid

For each of the reactions on your notes, determine if the reaction is a precipitation reaction or a neutralization reaction. Neutralization Reaction Precipitation Reaction Precipitation Reaction Neutralization Reaction Precipitation Reaction Neutralization Reaction Neutralization Reaction Precipitation Reaction Precipitation Reaction Neutralization Reaction Precipitation Reaction Neutralization Reaction Neutralization Reaction