TYPES OF CHEMICAL REACTIONS, CONTINUED

DOUBLE REPLACEMENT

• • •

Ions in two compounds “change partners” Cation of one compound combines with anion of the other General Equation:

AB + CD



AD + CB

DOUBLE REPLACEMENT PRODUCTS One of the compounds formed is usually either:

•

A precipitate

•

An insoluble gas that bubbles out of solution

•

Or, a molecular compound, usually water The other compound is often soluble and remains dissolved in solution.

DOUBLE REPLACEMENT EXAMPLE

Pb(NO 3 ) 2 (aq) + K 2 CrO 4 (aq)



PbCrO 4 (s) + 2KNO 3 (aq)

•Note how the ions combine to create neutral products

by crossing charges and simplifying.

•Then

…the equation is balanced.

ACID/BASE NEUTRALIZATION TYPE OF DOUBLE REPLACEMENT

•

When an acid reacts with a base, water a salt are produced. and

•

HCl + K(OH) → H(OH) + KCl

Switch Places

• •

H(OH) is water! (H 2 O) KCl is an ionic compound—a salt!

SOLID OR SOLUBLE?

When a double replacement reaction forms a SOLID solid , use the solubility rules on the back of your periodic table to tell which product is and which product is soluble . 3 AgNO 3 (aq) + K 3 PO 4 (aq)



3 KNO 3 + Ag 3 PO 4 (s) Rules 1 and 5 3 (NH 4 ) 2 S (aq) + 2 AlCl 3 (aq)



6 NH 4 Cl (aq) + Al 2 S 3 (s) Rules 1or 3 and 5