Precipitation Reactions Dont write Chemical Equations Chemical Reaction

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 CO 2 (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 - You. Tube • Double Replacement - Production of Precipitate • Orange tornado – You. Tube

• Are these compounds soluble or insoluble? (soluble =aq, insoluble = s) 1. K 2 SO 4 2. Ag. Cl 3. Ca. I 2 4. K 3 PO 4

Always 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 *HNO 3 • Base – Has a hydroxide (OH) *Li. OH *Ca(OH)2 • Salt – An ionic compound *Na. Cl *NH 4 PO 4

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 H 3 PO 4 + Li. OH →

• Fe(OH)2 + HBr →

H 2 CO 3 + Ca(OH)2 →

What reaction will produce the salt K 2 SO 4

Reduction – Oxidation Reactions (Redox)

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

Example 2 Na + Cl 2 (Na is not gaining or losing e-) → 2 Na. Cl → (Na loses 1 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 O 2 S 8 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 _____|_____ -2 -1 0 1 2 Oxidized

Examples:

Non-Example HCl + Na. OH → (Na loses 1 e-) Na. Cl + H 2 O (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) *Has a “free element” A + BC → B + AC AB → 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 + H 2 O

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.