AP CHEMISTRY UNIT 8 TYPES OF REACTIONS

General Guidelines Equations are usually found in the free-response section of the AP test. You are expected to: write balanced net ionic equations for reactions when given the reactants The first thing to note is that all AP equations "work". In each case, a reaction will occur. answer a question or use the equation to solve for needed values

General point guidelines : Each reaction earn points, generally for the correct reactants and products, as well as balancing. Leaving in the spectator ions will result point deductions. If you are uncertain of how to write a reaction, at least write something that is balanced! You can still use the equation to solve the problem, you just won’t get the equation points.

Types of Chemical Reactions (this isn’t all - more coming later!) Precipitation Reactions Acid/Base Neutralization Redox Reactions: Decomposition Synthesis/Addition Combustion

Precipitation Reactions A precipitate is an insoluble substance formed by the reaction of two aqueous substances. Two ions bond together so strongly that water can not pull them apart.

Predicting the Precipitate: Simple Rules for Solubility 1. Nitrate (NO3) compounds are soluble. 2. Alkali metal compounds and NH4+ are soluble. 3. Most Cl, Br, and I salts are soluble (NOT Ag+, Pb2+, Hg22+) 4. Most sulfate salts are soluble (NOT BaSO4, PbSO4, HgSO4, CaSO4) 5. Most OH salts are only slightly soluble (NaOH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble) 6. Most S2, CO32, CrO42, PO43 salts are only slightly soluble.

Extra Solubility Information Ca(OH)2 and Sr(OH)2 are moderately soluble and can be written together or as ions. Ba(OH)2 is typically soluble and Mg(OH)2 is insoluble. CaSO4 and SrSO4 are moderately soluble and can be written together or as ions. Weak electrolytes, such as acetic acid, are not ionized. Solids and pure liquids are written together, also. A saturated solution is written in ionic form while a suspension is not ionized.

AgNO3(aq) + LiBr(aq)  AgBr(s) + LiNO3(aq) Example: Write the equation for the precipitation reaction that occurs when solutions of silver nitrate and lithium bromide are mixed. AgNO3(aq) + LiBr(aq)  AgBr(s) + LiNO3(aq)

Practice: Write the balanced equation for the reaction shown below:

Three types of chemical equations for Precipitation Reactions: 1. molecular equation -overall reaction stoichiometry 2. complete ionic equation -all compounds that form ions in water are represented as ions 3. net ionic equation -spectator ions are not included

Molecular equation: 1. NaCl(aq) + AgNO3(aq)  NaNO3(aq) + AgCl(s) Complete ionic equation: 2. Na+ (aq) + Cl(aq) + Ag+(aq) + NO3(aq)  Na+(aq) + NO3(aq) + AgCl(s) Net ionic equation: 3. Cl(aq) + Ag+(aq)  AgCl(s)

Time-out for LAB Mystery of the 7 Solution - Complete Lab WS - Separate sheet of Paper: Equation & Net Ionic

Gravimetric analysis- quantitative lab procedure where a precipitate containing the substance is formed, filtered, dried & weighed. Calculations with Precipitation Reactions:

The zinc in a 1.2000g sample of foot powder was precipitated as ZnNH4PO4. Strong heating of the precipitate yielded 0.4089 g of Zn2P2O7. Calculate the mass percent of zinc in the sample of the foot powder. 0.4089gZn2P2O7 1 mol Zn2P2O7 2 mol Zn 65.37g = 304.7 g 1 mol Zn2P2O7 1 mol Zn 0.1754g Zn × 100 = 14.62% Zn 1.200g sample

A mixture contains only NaCl and Fe(NO3)3. A 0 A mixture contains only NaCl and Fe(NO3)3. A 0.456g sample of the mixture is dissolved in water, and an excess of NaOH is added, producing a precipitate of Fe(OH)3. The ppt is filtered, dried, & weighed. Its mass is 0.128g. Calculate: a. the mass of the iron b. the mass of Fe(NO3)3 c. the mass percent of Fe(NO3)3 in the sample 0.128g Fe(OH)3 1 mol Fe(OH)3 1 mol Fe 55.85g Fe= 0.0669g Fe 106.9g Fe(OH)3 1 mol Fe(OH)3 1 mol Fe 0.0669g Fe 1 mol Fe 1 mol Fe(NO3)3 241.9g Fe(NO3)3= 0.290g Fe(NO3)3 55.85g Fe 1 mol Fe 1 mol Fe(NO3)3 0.290g × 100 = 63.6% Fe(NO3)3 0.456g

Acid-Base Reactions Brønsted-Lowry acid-base definitions: acid- proton donor base- proton acceptor

Neutralization When a strong acid reacts with a strong base the net ionic reaction is: H+(aq) + OH-(aq) H2O(l) Watch out for information about quantities of each reactant!

Strong and Weak Acids and Bases Remember which acids are strong (ionize completely) and which are weak (write as molecule). Only one H+ ionizing at a time. Sulfuric acid solution (strong acid) should be written as H+ and HSO4-. Concentrated strong acids must be left together as they do not have enough water to ionize.