CHEM 200/202 Professor Jing Gu Office: EIS-210 All emails are to be sent to: chem200@mail.sdsu.edu My office hours will be held in GMCS-212 on Monday from 9 am to 11 am or by appointment.
ANNOUNCEMENTS Chapter 2 homework due 9/14/18 Lab report Volumetric Equipment and Pre-Lab assignment and report: Qualitative Analysis is due on 9/17/18 Quiz 1 due 9/20/18. Homework Chapter 3 and 4 due 9/21/18. Exam 1 is on 9/22/18 at 2-4 pm.
LECTURE OBJECTIVES Chapter 4.1-4.2 Balance chemical reactions. Express aqueous ionic reactions in various manners. Identify spectator ions in aqueous ionic reactions. Identify precipitates in aqueous ionic reactions.
BALANCING CHEMICAL EQUATIONS It is crucial to have properly balanced reactions when trying to interpret chemical reactions. The balanced reaction shows us how much of each reagent is required and how much of each product is formed. Methane (CH4) undergoes a combustion reaction with oxygen (O2), producing carbon dioxide (CO2) and water (H2O).
BALANCE THE REACTIONS BELOW _N2(g) + _H2(g) _NH3(g) _Pb(s) + _H2O(l) +_O2(g) _Pb(OH)2(s)
IONIC REACTIONS Many chemical reactions which take place in aqueous solutions involve ionic compounds. These ionic reactions can be depicted in various forms depending on how we wish to focus our attention. The various forms include: The molecular equation The complete ionic equation The net ionic equation
IONIC EQUATIONS Sample reaction: lead nitrate reacting with potassium iodide. The molecular equation Pb(NO 3 ) 2(aq) + 2KI (aq) PbI 2(s) + 2KNO 3(aq) The reaction depicts the molecular reactants and products, but does not show the ions present in solution.
IONIC EQUATIONS Pb(NO 3 ) 2(aq) + 2KI (aq) PbI 2(s) + 2KNO 3(aq) Dissociation of ionic compounds: Pb(NO 3 ) 2(aq) Pb 2+ (aq) + 2NO 3 (aq) KI (aq) K + (aq) + I (aq) KNO 3(aq) K + (aq) + NO 3 (aq) PbI 2(s) PbI 2(s) (There are no ions, lead iodide is insoluble in water.) Complete ionic equation: Pb 2+ (aq) + 2NO 3 (aq) + 2K + (aq) + 2I (aq) PbI 2(s) + 2K + (aq) + 2NO 3 (aq)
IONIC EQUATIONS The net ionic equation is a simplification of the complete ionic equation. The net ionic equation removes all the spectator ions. Pb 2+ (aq) + 2NO3 (aq) + 2K + (aq) + 2I (aq) PbI2(s) + 2K + (aq) + 2NO3 (aq) Net ionic equation: Pb 2+ (aq) + 2I (aq) PbI2(s)
REACTION CLASSIFICATIONS There are three principle aqueous chemical reactions that we will focus on in this course: Precipitations reactions Acid-base reactions Redox reactions (oxidation-reductions)
PRECIPITATION REACTIONS https://www.youtube.com/watch?v=2eqzngpzy5a Precipitation reactions occur when pairs of insoluble ions (e.g. Ag + and Cl ) are both present in solution at the same time. A mixture of aqueous solutions may result in more than one precipitate being formed, if more than one insoluble pair is present. Knowledge of the common soluble and insoluble ions is required to predict precipitations (solubility rules).
Soluble SOLUBILITY RULES 1. All common compounds of Group 1A(1) ions (Li +, Na +, K +...) and ammonium ions (NH4 + ) 2. All common nitrates (NO3 - ), acetates (CH3CO2 - ) and most perchlorates (ClO4 - ) 3. All common chlorides (Cl - ), bromides (Br - ) and iodides (I - ); except those of Ag +, Pb 2+, Cu + and Hg2 2+. All common fluorides (F - ) are soluble; except for Pb 2+ & Group2A(2) 4. All common sulfates (SO4 2- ); except Ca 2+, Sr 2+, Ba 2+, Ag + & Pb 2+
SOLUBILITY RULES Insoluble 1) All common metal hydroxides are insoluble; except those of Group 1A(1) and the larger members of Group 2A(2) - beginning with Ca 2+. 2) All common carbonates (CO3 2- ) and phosphates (PO4 3- ) are insoluble; except those from Group 1A(1) and ammonium (NH4 + ). 3) All common sulfides (S 2- ) are insoluble; except those of Groups 1A(1), 2(A)2 and NH4 +.
PREDICTING PRECIPITATION 1. Note the ions present in the reactants. 2. Consider the possible cation-anion combinations. 3. Decide wether any of the ion combinations is insoluble.
QUESTION Predict the identity of the precipitate formed when solutions of Na2CO3 and CaCl2 are mixed. Answers A B C D E Na2CO3 CaCl2 CaCO3 NaCl No ppt forms
PREDICTING PRECIPITATION For the following aqueous reactions, does a precipitate form? Write the net ionic equation for the reaction, if applicable. Potassium nitrate + Silver(I) acetate Sodium iodide + Copper(I) nitrate
PROBLEM Balance the reaction below, and provide the net ionic equation for the reaction. _Fe(NO3)3(aq) + _Na2CO3(aq) _Fe2(CO3)3(s) + _NaNO3(aq)
LECTURE OBJECTIVES Chapter 4.2-4.3 Identify acid-base reactions and their respective products. Calculate acid-base neutralization endpoints.
ACIDS AND BASES Acids - produce H3O + (aq) when dissolved in water (often expressed as H + (aq)) Bases - produce OH (aq) when dissolved in water Strong acid/base - completely dissociates in water Weak acid/base - incompletely dissociates in water
ACID BASE THEORY H + (proton) forms H 3 O + in water (hydrogen bonding) H + is electron deficient, wants electrons, electron pair acceptor OH is electron rich, can donate a pair of electrons Water self-ionizes: 2H2O(l) H3O + (aq) + OH (aq) Acid-Base definitions: Arrhenius: Acid increases conc. of H3O + when added to water Base increases conc. of OH - when added to water Brønsted-Lowry: Acid = proton donor Base = proton acceptor Lewis: Acid: electron pair acceptor Base: electron pair donor
ACID-BASE THEORY Arrhenius example: NaOH (aq) + HCl (aq) H2O(l) + NaCl(aq) Net ionic equation for all Arrhenius acid-base reactions: H + (aq) + OH (aq) H2O(l) Brønstead example: HCl(benzene) + NH3(benzene) NH4Cl(s) HCl donates a proton to NH3 Lewis example: NH3(g) + BH3(g) NH3BH3
SELECTED ACIDS & BASES Strong Acids Hydrochloric acid, HCl Hydrobromic acid, HBr Hydroiodic acid, HI Nitric acid, HNO3 Sulfuric acid, H2SO4 Perchloric acid, HClO4 Weak Acids Hydrofluoric acid, HF Phosphoric acid, H3PO4 Acetic acid, CH3COOH (or HC2H3O2) Strong Bases Sodium hydroxide, NaOH Potassium hydroxide, KOH Calcium hydroxide, Ca(OH)2 Strontium hydroxide, Sr(OH)2 Barium hydroxide, Ba(OH)2 Weak Bases Ammonia, NH3
ACIDS Monoprotic: one ionizable hydrogen HCl + H 2 O H 3 O + + Cl Diprotic: two ionizable hydrogens H 2 SO 4 + H 2 O H 3 O + + HSO 4 HSO 4 + H 2 O H 3 O + + SO 4 2 Triprotic: three ionizable hydrogens Polyprotic, generic term meaning that there is more than one ionizable hydrogen on the molecule. H 3 PO 4 + H 2 O H 3 O + + H 2 PO 4 H 2 PO 4 + H 2 O H 3 O + + HPO 4 2 HPO 4 2 + H 2 O H 3 O + + PO 4 3
BASES Monobasic: yields one OH - ion KOH K + + OH NH3 +H2O NH4 + + OH Dibasic: yields two OH ions Ba(OH)2 Ba 2+ + 2OH Ca(OH)2 Ca 2+ + 2OH
ACID-BASE NEUTRALIZATION Molecular equation Acid + Base Water + Salt Total ionic equation HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) H + (aq) + Cl (aq) + Na + (aq) + OH (aq) H2O(l) + Na + (aq) + Cl (aq) Net ionic equation H + (aq) + OH (aq) H2O(l) Hint: Balance the H + with OH - the rest will work itself out.
AN AQUEOUS STRONG ACID-BASE REACTION ON THE ATOMIC SCALE
ACID-BASE TITRATION
QUESTION What is the concentration of a sulfuric acid solution if it requires 26.05 ml of a 2.045 M sodium hydroxide solution to titrate 12.05 ml of the sulfuric acid solution?
GAS FORMATION WITH AN ACID-BASE Molecular equation REACTION NaHCO3(aq) + CH3CO2H(aq) H2O(l) + CH3CO2Na(aq) + CO2(g) Total ionic equation Na + (aq) + HCO3 - (aq) + H + (aq) + CH3CO2 - (aq) H2O(l) + Na + (aq) + CH3CO2 - (aq) + CO2(g) Net ionic equation HCO3 - (aq) + CH3CO2H(aq) CH3CO2 - + H2O(l) + CO2(g)
An aqueous solution of H 2 SO 4 is added to an aqueous solution of Ba(OH) 2. The reaction is monitored using a conductivity meter. Predict the correct statement(s): 1. Both H 2 SO 4 & Ba(OH) 2 are strong electrolytes 2. This is a neutralization reaction 3. This is a precipitation reaction 4. The light bulb will glow at the neutralization point Answers A B C D E Statement 2 Statements 1 & 2 Statements 1, 2 & 3 All of the statements are true All of the statements are lies