Unit 4 (Chapter 4): Aqueous Reactions & Solution Stoichiometry John D. Bookstaver St. Charles Community College St. Peters, MO  2006, Prentice Hall, Inc. Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten

Solutions: homogeneous mixtures: evenly mixed (same) solvent is present in greatest abundance. solute dissolved in/by solvent +

0.250 L Molarity Molarity (M) is a measure of the concentration of a solution. moles of solute (mol) liters of solution (L) Molarity (M) = units:mol/L or mol ∙ L –1 What’s the concentration of a solution with 29.2 g of sodium chloride in 250. mL of water? 29.2 g NaCl x 1 mol NaCl g NaCl = mol NaCl = 2.00 M NaCl

Solution Prep from Solid 1-Calc & Mass solute 2-Add solvent, swirl to dissolve 3-Fill with DI water to mark 4-Mix (Cap & Invert to mix evenly) WS #1-2 Conc. Calc’s

WS Concentration & Dilutions mol NaHCO g NaHCO 3 x 1 mol NaHCO g NaHCO 3 x 1 L NaHCO 3 = L NaHCO 3 #1 1 mol CuSO L CuSO 4 x 1.20 mol CuSO 4 1 L CuSO 4 x g CuSO 4 = 52.7 g CuSO 4 #2

1-Calc M 1 V 1 =M 2 V 2 2-Pipet V 1 from concentrated 3-Fill to mark with DI water 4-Mix (Cap & Invert to mix evenly) M 1 V 1 = M 2 V 2 Solution Prep by Dilution WS #3-4 Dilutions

WS Concentration & Dilutions #3 #4 M 1 V 1 = M 2 V 2 (12.0 M)V 1 = (1.25 M)(500. mL) V 1 = 52.1 mL (or L) M 1 V 1 = M 2 V 2 (2.50 M)V 1 = (0.200 M)(250. mL) V 1 = 20.0 mL (or L) HW p.160 #60, 67

HCl + H 2 O  H 3 O + + Cl – H H H H H H O O Cl + – NH 3 + H 2 O  NH OH – H H H H H H H H H H N O O N + –  Acid: proton (H + ) donor  Base: proton (H + ) acceptor

Strength of Acids and Bases (complete ionization) (completely as ions) HA (aq) H + (aq) + A – (aq) MOH (aq) M + (aq) + OH – (aq) (partial ionization) (mostly as molecules) HA (aq) + H 2 O (l) H 3 O + (aq) + A – (aq) B (aq) + H 2 O (l) BH + (aq) + OH – (aq) STRONG: WEAK:

Strong Acids: Only 6 strong acids: Nitric (HNO 3 ) Sulfuric (H 2 SO 4 ) Hydrochloric (HCl) Hydrobromic (HBr) Hydroiodic (HI) Perchloric (HClO 4 ) proton (H + ) donors HI + H 2 O  H 3 O + + I –

Strong Bases: The strong bases are soluble hydroxides (OH – ) of… Group 1 (Li,Na,K) CBS (Ca, Ba, Sr) Mg(OH) 2 & Be(OH) 2 are not soluble proton (H + ) acceptors OH – + H 3 O +  H 2 O + H 2 O ase Hydroxides of Group I and CBS

Salts: Ionic Solids: (metal-nonmetal) dissociate (dissolve) by separation into ions Electrolytes: ions in solution that conduct electricity

StrongWeak C 11 H 22 O 11 CH 3 OH H 2 O Non CH 3 COOH HNO 2 NH 3 NaOH HNO 3 KCl completely dissociate partially ionize only molecules NO ions ALL ions SOME ions HW p.159 #33

Electrolytes: Strong, Weak, or Non? Compound Ionic STRONG Molecular Acid (H____) STRONG (6) WEAK Not Acid NON HW p.157 #1,2,4,5,38 nonmetals (Covalent)metal-nonmetal C 11 H 22 O 11 C 2 H 5 OH H 2 O CH 3 COOH HNO 2 HF KBr CaI 2 FeCl 3 NaOH Ca(OH) 2 (strong bases) HCl, HBr, HI HNO 3 H 2 SO 4 HClO 4 (ions conduct electricity) Weak Base (& NH 3 )

Electrolytes: Strong, Weak, or Non? Compound Ionic STRONG Molecular Acid (H____) WEAK Not Acid NON nonmetals (Covalent)metal-nonmetal STRONG (6) QUIZ!!! (at the bell) Weak Base (& NH 3 )

Cl Na H O strong acid (H + A – ) strong base (M + OH – ) HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) ACID + BASE SALT + WATER HH H O Cl +– ionic compound (M + A – ) water H 2 O (HOH) Acid-Base Neutralization Reactions HW p.158 #40a

Double Replacement:(precipitate) precipitate: insoluble product (as predicted by solubility rules) Precipitation Reactions Pb 2+ I–I–

ALWAYS Soluble ions: Li +, Na +, K +,... Group I (alkali metals) NH 4 + ammonium NO 3 – nitrate Solubility Rules Common Precipitates form with:examples Ag +, Pb 2+, Hg 2+ (AP/H)AgCl, PbI 2 OH – (hydroxide)Cu(OH) 2 CO 3 2 – (carbonate)CaCO 3 ****** WS Solubility & NIE’s #1

Molecular Equation reactants and products in molecular form AgNO 3 (aq) + KCl (aq)  AgCl (s) + KNO 3 (aq) Ionic Equation Strong Electrolytes are Dissociated as ions (strong acids, strong bases, soluble salts) Ag + (aq) + NO 3 – (aq) + K + (aq) + Cl – (aq)  AgCl (s) + K + (aq) + NO 3 – (aq)

Net Ionic Equation (NIE) Ag + (aq) + NO 3 – (aq) + K + (aq) + Cl – (aq)  AgCl (s) + K + (aq) + NO 3 – (aq) NIE:Ag + (aq) + Cl – (aq)  AgCl (s) Cross out Spectator Ions (no change) only species left are those that react (change) during the course of the reaction. Net (same state) (same charge)

Balanced Net Ionic Equations 1. Write a Complete molecular equation. 2. Dissociate all strong electrolytes (aq). 3. Cross out spectators (same charge & state) 4. Write the Net ionic equation with the species that remain. 5. Balance the NIE. comp – diss – cross – net – bal (solubility rules)

BaSO 4 + NH 4 NO 3 Balanced Net Ionic Equations 1)(NH 4 ) 2 SO 4 + Ba(NO 3 ) 2 → 2)NaOH + MgBr 2 → comp – diss – cross – net – bal +2–2+––+ Ba 2+ + SO 4 2– → BaSO 4 NaBr + Mg(OH) 2 +–2+––+ Mg OH – → Mg(OH) 2 (s) HW p.158 #21

HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) H + + Cl – + Na + + OH –  Na + + Cl – + H 2 O Neutralization Reactions H + + OH –  H 2 O When a Strong Acid reacts with a Strong Base, the net ionic equation is…

HF (aq) + KOH (aq)  KF (aq) + H 2 O (l) HF + Na + + OH –  Na + + F – + H 2 O Neutralization Reactions HX + OH –  X – + H 2 O HW p.159 #40 (finish) When a Weak acid reacts with a Strong base, the net ionic equation is… (dissociate ONLY STRONG electrolytes)

BaSO 4 + NH 4 NO 3 Balanced Net Ionic Equations (NH 4 ) 2 SO 4 + Ba(NO 3 ) 2 → comp – diss – cross – net – bal +2–2+––+ Ba 2+ + SO 4 2– → BaSO 4 (s) HF (aq) + KOH (aq)  KF (aq) + H 2 O (l) WS Solubility & NIE’s #2 HF + OH –  F – + H 2 O –+–+

Gas-Forming Reactions Single Rep: Metal + Acid Metal Ion + H 2 Ex: Zn (s) + H 2 SO 4 (aq) ZnSO 4 (aq) + H 2 (g) NIE: Zn (s) + 2 H + (aq) Zn 2+ (aq) + H 2 (g) H 2 Demo (M 0 )(H + )(M + )(gas) +2– 2+2– Double Rep: Acid + Carbonate Salt + Ex: HCl (aq) + CaCO 3 (s) CaCl 2 (aq) + H 2 O (l) + CO 2 (g) NIE: 2 H + (aq) + CaCO 3 (s) Ca 2+ (aq) + H 2 O (l) + CO 2 (g) (or Bicarbonate) (HCO 3 – ) (CO 3 2– ) (H + ) CH 3 COOH + NaHCO 3  CH 3 COONa +H 2 O + CO 2 HW p. 159 #43 H 2 CO 3 (aq) H 2 O (l) + CO 2 (g) (decomposes immediately) (gas) CO 2 Demo

g A L of A g B mol BL of B g A 1 mol A mol A 1 L g B 1 mol B mol B 1 L molar mass A molar mass B molarity A (M) molarity B (M) mol-to-mol ratio mol A Rxn: A (aq) + 2 B (aq)  C + 2 D Solution Stoichiometry HW p. 161 #81

Oxidation-Reduction Reactions (REDOX) video clip (One cannot occur without the other) LEO says GER

Oxidation Numbers Is it a redox reaction? To find out… 1)assign oxidation numbers* (or oxidation states) to each element in a reaction. 2)check if any oxidation states changed ( ↓ reduced, ↑ oxidized) of elements describe electrons that would be lost or gained IF the compound was 100% ionic. *oxidation numbers *charges in H 2 O, O –2 of ions show electrons transferred IN an ionic compound in Na 2 O, O 2–

 F is always −1.  other halogens are −1, BUT can be positive, like in oxyanions. Ex. ClO 3 – or NO 3 – or SO 4 2– Assigning Oxidation Numbers 1.All pure elements are 0 2.Monatomic ion is its charge (Mg 2 + has +2) 3.Most nonmetals tend to be negative, but some are positive in certain compounds or ions.  O is −2 always  H is +1 with nonmetals, −1 with metals O is –2 but S is +6)(in SO 3, but in peroxide ion is −1 (O 2 2– )

Oxidation Numbers The sum of the ox. #’s in a neutral compound is 0. The sum of the ox. #’s in a polyatomic ion is the charge on the ion. Determine the oxidation number of: Sulfur in… SO 2 Chromium in… K 2 Cr 2 O 7 Nitrogen in… NH 4 + Cobalt in… [CoCl 6 ] 3–

Classifying REDOX Reactions All rxns (but…NOT double replacement) Decomposition AB → A + B1 → 2 (+/– → 0 0) Combustion C x H y + O 2 → CO 2 + H 2 O (–/+ 0 → +/– +/–) Single Replacement AB + C → A + CB (+/– 0 → 0 +/–) Synthesis A + B → AB2 → 1 (0 0 → +/–)

Single Replacement (REDOX) Cu 2+ (aq) + 2 Ag (s)  Cu (s) + 2 Ag + (aq) X Cu (s) + 2 Ag + (aq)  Cu 2+ (aq) + 2 Ag (s) silver ions oxidize copper metal

Activity Series of Metals increasing ease of oxidation Cannot displace H + from acid to make H 2 (g)

Write the net ionic equation for the reaction of solid zinc in a solution of hydrochloric acid. Writing REDOX Reactions Mg (s) + HCl (aq)  MgCl 2 (aq) + H 2 (g) comp – diss – cross – net – bal 0+1–1+2–10 Mg + H +  Mg +2 + H 2 2 Classify the reaction in two ways. Single-Replacement and Redox

Mg + 2 H +  Mg 2+ + H 2 (g) WS Aq Soln’s & Chem Rxns What is red & what is ox? red ox