Reactions in Aqueous Solutions Chapter 7 Basic Types

Reactions in Aqueous Solutions Chapter 7

Basic Types of Equations (Review of yesterday’s notes)

Synthesis element + element compound A+X AX aluminum + oxygen ? analogy=?

Decomposition compound element + element AX A+X water ? analogy=?

Single Replacement compound and element and compound AX+B A+BX chromium nitrate + copper ? analogy=?

Double Replacement compound and compound AX+BY AY+BX Silver carbonate + magnesium phosphate ? analogy=?

What type of reaction begins with one compound?

Decomposition

What type of reaction begins with one compound and one element?

Single Replacement

What type of reaction begins with two elements?

Composition or Synthesis

What type of reaction begins with two compounds?

Double Displacement

Advanced Types

Types of Reactions I. Precipitation reactions When aqueous solutions of ionic compounds are poured together a solid forms. A solid that forms from mixed solutions is a precipitate. If you’re not a part of the solution, your part of the precipitate.

Precipitation reactions 3 Na. OH(aq) + Fe. Cl 3(aq) 3 Na. Cl(aq) + Fe(OH)3(s) is really 3 Na+(aq)+3 OH-(aq) + Fe+3(aq) + 3 Cl-(aq) 3 Na+ (aq) + 3 Cl- (aq) + Fe(OH)3(s) So all that really happens is 3 OH-(aq) + Fe+3(aq) Fe(OH)3(s) Double replacement reaction

Precipitation reaction We can predict the products Can only be certain by experimenting The anion and cation switch partners Ag. NO 3(aq) + KCl(aq) ?

Precipitations Reactions Only happen if one of the products is insoluble Otherwise all the ions stay in solution- nothing has happened.

Solubility Rules (p 170) 1 All nitrates are soluble 2 Alkali metals ions and NH 4+ ions are soluble 3 Halides are soluble except Ag+, Pb+2, and Hg 2+2 4 Most sulfates are soluble, except Pb+2, Ba+2, Hg+2, and Ca+2

Solubility Rules 5 Most hydroxides are slightly soluble (insoluble) except Na. OH and KOH 6 Sulfides, carbonates, chromates, and phosphates are insoluble

Three Types of Equations 1) Molecular Equation- written as whole formulas, not the ions. K 2 Cr. O 4(aq) + Ba(NO 3)2(aq) 2 KNO 3(aq)+Ba. Cr. O 4(s) 2) Complete Ionic equation show dissolved electrolytes as the ions. 2 K+(aq) + Cr. O 4 -2(aq) + Ba+2(aq) + 2 NO 3 -(aq) Ba. Cr. O 4(s) + 2 K+ (aq) + 2 NO 3 - (aq) Spectator ions are those that don’t react.

Three Type of Equations 3) Net Ionic equations show only those ions that react, not the spectator ions Ba+2 (aq) + Cr. O 4 -2 (aq) Ba. Cr. O 4(s) Write three types of equations for the reactions when these solutions are mixed. iron (III) sulfate and potassium sulfide

Answer iron (III) sulfate and potassium sulfide Molecular Fe 2(SO 4)3 (aq) + 3 K 2 S (aq) Fe 2 S 3 (s) + 3 K 2 SO 4 (aq) In your book, rule 2 trumps rule 6. Ionic 2 Fe+3 (aq) + 3 SO 4 -2 (aq) + 6 K+1 (aq) + 3 S-2 (aq) Fe 2 S 3 (s) + 6 K+1 (aq) + 3 SO 4 -2 (aq) Net Ionic 2 Fe+3 (aq) + 3 S-2 (aq) Fe 2 S 3 (s)

Types of Reactions II. Acid-Base Acid + Base salt + water H+ + OH- H 2 O (often called a neutralization reaction). For our purposes an acid is a proton donor. A base is a proton acceptor usually OH What is the net ionic equation for the reaction of HCl(aq) and KOH(aq)?

Types of Reaction III. Oxidation-Reduction called Redox Ionic compounds are formed through the transfer of electrons. An Oxidation-reduction reaction involves the transfer of electrons. We need a way of keeping track.

Oxidation States A way of keeping track of the electrons. Not necessarily true of what is in nature, but it works. Need the rules for assigning (memorize). 1 The oxidation state of elements in their standard states is zero. 2 Oxidation state for monoatomic ions are the same as their charge.

Oxidation states 3 Oxide is assigned an oxidation state of -2 in its covalent compounds except as a peroxide. 4 In compounds with nonmetals hydrogen is assigned the oxidation state +1. 5 In its compounds fluoride is always – 1. 6 The sum of the oxidation states must be zero in compounds or equal the charge of the ion.

Oxidation States Assign the oxidation states to each element in the following. CO 2 NO 3 H 2 SO 4 Fe 2 O 3 Fe 3 O 4

Oxidation States Assign the oxidation states to each element in the following. +4 -2 CO 2 +5 -2 NO 3 +1 +6 -2 H 2 SO 4 +3 -2 Fe 2 O 3 +2. 66 -2 Fe 3 O 4 is actually Fe+3 Fe+2

Transfer of electrons Oxidation-loss of electrons Reduction-gain of electrons Oxidation/reduction reaction-metal/nonmetal reaction (sometimes nonmetals undergo ox/red if oxygen is a reactant) 2 Na(s)+Cl 2(g) 2 Na. Cl(s) Na + Cl Na++ Cloxidation reduction

Oxidation-Reduction Transfer electrons, so the oxidation states change. 0 0 +1 -1 Na + 2 Cl 2 2 Na. Cl +4 -1 0 +4 -2 +1 -2 CH 4 + 2 O 2 CO 2+ 2 H 2 O Oxidation is the loss of electrons. Reduction is the gain of electrons. OIL RIG LEO GER

Oxidation-Reduction Oxidation means an increase in oxidation state - lose electrons. Reduction means a decrease in oxidation state - gain electrons. The substance that is oxidized is called the reducing agent. The substance that is reduced is called the oxidizing agent.

Identify the Oxidizing agent Reducing agent Substance oxidized Substance reduced Fe (s) + O 2(g) Fe 2 O 3(s)+ 3 CO(g) 2 Fe(l) + 3 CO 2(g)

Combustion Reaction of a hydrocarbon/alcohol or other organic molecule with oxygen gas to produce carbon dioxide and water C 3 H 8 + 5 O 2 → 3 CO 2 + 4 HOH CH 3 CH 2 OH + 3 O 2 → 2 CO 2 + 3 HOH