Precipitation Reactions

Don’t write - Chemical Equations Chemical Reaction = new substance is produced. Reactants (R) – left of arrow Products (P) – right of arrow

Don’t Write - Indications of a Chemical Reaction Evolution of heat/light Exothermic (releases heat) Endothermic (absorbs heat) Production of a gas Formation of a precipitate (solid) Color change

Vocabulary to Know Soluble – will dissolve (aq) Insoluble – will not dissolve (s) Examples: Sand ??? Sugar ??? Salt ??? Dirt ???

Aqueous Solution – homogeneous mixture of a soluble compound dissolved in water Precipitate – a solid formed in solution Cation – positive ion (written first in a compound) Anion – negative ion (written last in a compound)

Precipitation Reaction (also called): *Double Replacement *Ion switch Ions of 2 aqueous reactants exchange places and form 2 new products (need volunteers)

Symbols used in Equations  - yields (=) The following are written to the right of the compound in a reaction: (g) – gas CO2 (g) (s) – solid (l) – liquid (aq) – aqueous (dissolved in water)

One product will be soluble (aq) (dissolved in water – liquid). One product will be insoluble (s) - exist as a solid (it will precipitate out of solution)

Soluble or Insoluble?? Check the solubility of common ionic compounds on reference materials sheet Indicate which product is soluble and which is insoluble!!!!!

Precipitation reactions - YouTube Double Replacement - Production of Precipitate Orange tornado – YouTube

Are these compounds soluble or insoluble? (soluble =aq, insoluble = s) K2SO4 2. AgCl CaI2 4. K3PO4

Always Soluble Usually Soluble Usually Insoluble

Precipitation examples 1. Zinc nitrate(aq) + ammonium sulfide(aq)→ ? 2. Calcium hydroxide(aq) + ammonium sulfate (aq)→

Acid-Base Reactions Neutralization

Acid – Begins with hydrogen (H). *HCl *HNO3 Base – Has a hydroxide (OH) *LiOH *Ca(OH)2 Salt – An ionic compound *NaCl *NH4PO4

Acid Base Reaction Acid and base reacts to form WATER and a SALT. - Balance the charges of the salt (+ comes from the base and neg comes from the acid)

Balance salts and then entire equation Example H3PO4 + LiOH →

Fe(OH)2 + HBr →

H2CO3 + Ca(OH)2 →

What reaction will produce the salt K2SO4

Reduction – Oxidation Reactions (Redox)

Involves a transfer of electrons (gaining and losing). Reaction will have a free element.

Example 2 Na + Cl2 → 2 NaCl (Na is not gaining → (Na loses 1 e-) or losing e-) This is a redox reaction because Sodium has to lose electrons to bond with chlorine. And… chlorine gains electrons to bond with sodium.

Assigning oxidation numbers: 1. THE SUM OF OXIDATION NUMBERS (states) IN A COMPOUND WILL EQUAL ZERO. 2. Uncombined elements are 0 (zero). example: Cu O2 S8 3. Hydrogen and group I = + 1 4. Group II = +2 5. Oxygen = -2 6. Fluorine = -1

Examples:

Compare oxidation states from reactant to product: **Increases (loses electrons) – Oxidized **Decreases (gains electrons) – Reduced _________|_________ Reduced -2 -1 0 1 2 Oxidized

Examples:

Non-Example HCl + NaOH → NaCl + H2O (Na loses 1 e-) (Na loses 1 e-) Acid-Base and Precipitation reactions are NOT redox because the charge (oxidation state), on the product side is the same as the reactant side.

1. Redox reactions (reduction-oxidation) 1. Redox reactions (reduction-oxidation) *Has a “free element” A + BC → B + AC AB → A + B A + B → AB

2. Neutralization Reactions (Acid-Base) *Reactants are an acid – (Starts with H), and a base (ends with OH - hydroxide) *Always produces water. H A + B OH → BA + H2O

3. Precipitation reactions (ion switch) *Has two compounds reacting (no free elements). *Forms a solid product (precipitate) AB + CD → AD + CB

Note to self – add reagents and assigning oxidation states and number line.