Exp 16 video time 1 hr and 23

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Exp. 16 – video (time: 1 hr and 23: 08 minutes) Exp. 16: Volumetric

Exp. 16 – video (time: 1 hr and 23: 08 minutes) Exp. 16: Volumetric Analysis: Redox Titration Normality = eq wt of solute L solution Acid/bases: #eq = # H+ or OH- ionized Redox reactions – transfer of ereduction – oxidation reactions

Redox reaction Equivalent wt - one equivalent of any oxidizing agent reacts with one

Redox reaction Equivalent wt - one equivalent of any oxidizing agent reacts with one equivalent of any reducing agent. This means #eq/mol is equal to the number of e- transferred. Mn. O 4 -(aq) + 8 H+(aq) + 5 e- Mn 2+(aq) + 4 H 2 O(l) Mn. O 4 - : 5 eq mol Mn. O 4 Fe 2+(aq) Fe 3+(aq) + 1 e- same for KMn. O 4 1 eq mol Fe 2+ (net)

N M or M N N (eq) = M (mol) x #eq L L

N M or M N N (eq) = M (mol) x #eq L L mol Note: N equal to or greater than M 0. 1 M KMn. O 4 N? Goal: eq KMn. O 4 L soln Mn. O 4 -(aq) + 8 H+(aq) + 5 e- Mn 2+(aq) + 4 H 2 O(l) Calc:

Solubility Rules for Ionic Compounds (Dissociates 100%) 1. ) All compounds containing alkali metal

Solubility Rules for Ionic Compounds (Dissociates 100%) 1. ) All compounds containing alkali metal cations and the ammonium ion are soluble. 2. ) All compounds containing NO 3 -, Cl. O 4 -, Cl. O 3 -, and C 2 H 3 O 2 - anions are soluble. 3. ) All chlorides, bromides, and iodides are soluble except those containing Ag+, Pb 2+, or Hg 22+. 4. ) All sulfates are soluble except those containing Hg 22+, Pb 2+, Ba 2+, Sr 2+, or Ca 2+. Ag 2 SO 4 is slightly soluble. 5. ) All hydroxides are insoluble except compounds of the alkali metals and Ca 2+, Sr 2+, and Ba 2+ are slightly soluble. 6. ) All other compounds containing PO 43 -, S 2 -, CO 32 -, Cr. O 42 -, SO 32 - and most other anions are insoluble except those that also contain alkali metals or NH 4+. Generally, compound dissolves Hg 2 Cl 2 (s) KI (aq) Pb(NO 3)2 (aq) insoluble > 0. 10 M - soluble (aq) < 0. 01 M - insoluble (s) in between - slightly soluble (this class we will assume slightly soluble as soluble) 4

Strong Acids (Ionizes 100%) HCl, HBr, HI, HCl. O 4, HNO 3, H 2

Strong Acids (Ionizes 100%) HCl, HBr, HI, HCl. O 4, HNO 3, H 2 SO 4 Strong Bases (Dissociates 100%) Na. OH, KOH, Li. OH, Ba(OH)2, Ca(OH)2, Sr(OH)2 5

Ions in Aqueous Solution Molecular and Ionic Equations • A molecular/formula unit equation is

Ions in Aqueous Solution Molecular and Ionic Equations • A molecular/formula unit equation is one in which the reactants and products are written as if they were molecules/formula units, even though they may actually exist in solution as ions. Calcium hydroxide + sodium carbonate M. E. Ca(OH)2 (aq) + strong base Na 2 CO 3 (aq) Ca. CO 3 (s) + 2 Na. OH (aq) soluble salt insoluble salt strong base s solid l liquid aq aqueous (acid/bases and soluble salts dissolve in water) g gases 6

Ions in Aqueous Solution Molecular and Ionic Equations • An total ionic equation, however,

Ions in Aqueous Solution Molecular and Ionic Equations • An total ionic equation, however, represents strong electrolytes as separate independent ions. This is a more accurate representation of the way electrolytes behave in solution. – A complete ionic equation is a chemical equation in which strong electrolytes (such as soluble ionic compounds, strong acids/bases) are written as separate ions in solution. (note: g, l, insoluble salts (s), weak acid/bases do not break up into ions) M. E. Ca(OH)2 (aq) + strong base Na 2 CO 3 (aq) Ca. CO 3 (s) + 2 Na. OH (aq) soluble salt insoluble salt strong base Total ionic Ca 2+ (aq) + 2 OH- (aq) + 2 Na+ (aq) + CO 32 - (aq) Ca. CO 3 (s) + 2 Na+ (aq) + 2 OH- (aq) 7

Net ionic equations. – A net ionic equation is a chemical equation from which

Net ionic equations. – A net ionic equation is a chemical equation from which the spectator ions have been removed. – A spectator ion is an ion in an ionic equation that M. E. does not take part in the reaction. Ca(OH)2 (aq) + Na 2 CO 3 (aq) Ca. CO 3 (s) + 2 Na. OH (aq) Total Ionic Ca 2+ (aq) + 2 OH- (aq) + 2 Na+ (aq) + CO 32 - (aq) Ca. CO 3 (s) + 2 Na+ (aq) + 2 OH- (aq) Net Ca 2+ (aq) + CO 32 - (aq) Ca. CO 3 (s) 8

Types of Chemical Reactions • Oxidation-Reduction Reactions (Redox rxn) – Oxidation-reduction reactions involve the

Types of Chemical Reactions • Oxidation-Reduction Reactions (Redox rxn) – Oxidation-reduction reactions involve the transfer of electrons from one species to another. – Oxidation is defined as the loss of electrons. – Reduction is defined as the gain of electrons. – Oxidation and reduction always occur simultaneously. 9

27. 1 Reduction and Oxidation Redox reactions – transfer of ereduction – oxidation reactions

27. 1 Reduction and Oxidation Redox reactions – transfer of ereduction – oxidation reactions Reduction – gain of e- / gain of H / lost of O Fe 3+ + 1 e- Fe 2+ (lower ox state) note: must balance atoms and charges 10

Oxidation - loss of e- / loss of H / gain of O Fe

Oxidation - loss of e- / loss of H / gain of O Fe 2+ Fe 3+ + 1 e- (higher ox state) Br + 4(-2) = -1 Br = -1 +8 = +7 H 2 O + Br. O 3 - Br. O 4 - + 2 H+ + 2 e. Br + 3(-2) = -1 (Br oxidized: charge 5+ 7+) Br = -1 +6 = +5 2 H+ + 2 e- H 2 (H reduced: charge 1+ 0) Oxidizing agent is species that undergoes reduction. Reducing agent is species that undergoes oxidation. Note: need both for reaction to happen; can’t have something being reduced unless something else is being oxidized. 11

27. 3 Balancing Redox Reactions - Must know charges (oxidation numbers) of species including

27. 3 Balancing Redox Reactions - Must know charges (oxidation numbers) of species including polyatomic ions - Must know strong/weak acids and bases - Must know the solubility rules Oxidation Numbers – hypothetical charge assigned to the atom in order to track electrons; determined by rules. 12

Rules to balance redox 1. ) Convert to net ionic form if equation is

Rules to balance redox 1. ) Convert to net ionic form if equation is originally in molecular form (eliminate spectator ions). 2. ) Write half reactions. 3. ) Balance atoms using H+ / OH- / H 2 O as needed: – acidic: H+ / H 2 O put water on side that needs O or H (comes from solvent) – basic: OH- / H 2 O put water on side that needs H but if there is no H involved then put OH- on the side that needs the O in a 2: 1 ratio 2 OH- / H 2 O balance O with OH, double OH, add 1/2 water to other side. 4. ) Balance charges for half rxn using e-. 5. ) Balance transfer/accept number of electron in whole reaction. 6. ) Convert equation back to molecular form if necessary (re-apply spectator ions). 13

Zn(s) + Ag. NO 3(aq) Zn(NO 3)2(aq) + Ag(s) Total ionic: Zn(s) + Ag+(aq)

Zn(s) + Ag. NO 3(aq) Zn(NO 3)2(aq) + Ag(s) Total ionic: Zn(s) + Ag+(aq) + NO 3 -(aq) Zn 2+(aq) + 2 NO 3 -(aq) + Ag(s) Net ionic: Zn(s) + Ag+(aq) Zn 2+(aq) + Ag(s) 14

Net: Zn(s) + Ag+(aq) Zn 2+(aq) + Ag(s) Oxidation: Zn(s) Zn 2+(aq) + 2

Net: Zn(s) + Ag+(aq) Zn 2+(aq) + Ag(s) Oxidation: Zn(s) Zn 2+(aq) + 2 e- Reduction: [ 1 e- + Ag+(aq) Ag(s)] 2 Balanced net: Zn(s) + 2 Ag+(aq) Zn 2+(aq) + 2 Ag(s) Balanced eq: Zn(s) + 2 Ag. NO 3(aq) Zn(NO 3)2(aq) + 2 Ag(s) 15

Net: Mn. O 4 -(aq) + Fe 2+(aq) [ Fe 2+(aq) Fe 3+(aq) +

Net: Mn. O 4 -(aq) + Fe 2+(aq) [ Fe 2+(aq) Fe 3+(aq) + 1 e- ] 5 Ox: Red: H+ Mn 2+(aq) + Fe 3+(aq) 5 e- + 8 H+(aq) + Mn. O 4 -(aq) Mn 2+(aq) + 4 H 2 O(l) Balanced net: 8 H+(aq) + Mn. O 4 -(aq) + 5 Fe 2+(aq) Mn 2+(aq) + 5 Fe 3+(aq) + 4 H 2 O(l) 16

KMn. O 4(aq) + Na. NO 2(aq) + HCl(aq) Na. NO 3(aq) + Mn.

KMn. O 4(aq) + Na. NO 2(aq) + HCl(aq) Na. NO 3(aq) + Mn. Cl 2(aq) + KCl(aq) + H 2 O(l) Net: Mn. O 4 -(aq) + NO 2 -(aq) + H+(aq) NO 3 -(aq) + Mn 2+(aq) + H 2 O(l) + NO 2 -(aq) NO 3 -(aq) + 2 H+(aq) + 2 e- ] 5 Ox: [ Red: [ 5 e- + 8 H+(aq) + Mn. O 4 -(aq) Mn 2+(aq) + 4 H 2 O(l) ] 2 Balanced net: 2 Mn. O 4 -(aq) + 5 NO 2 -(aq) + 16 H+(aq) + 5 H 2 O(l) 2 Mn 2+(aq) + 8 H 2 O(l) + 5 NO 3 -(aq) +10 H+(aq) 2 Mn. O 4 -(aq) + 5 NO 2 -(aq) + 6 H+(aq) 2 Mn 2+(aq) + 3 H 2 O(l) + 5 NO 3 -(aq) Balanced eq: 2 KMn. O 4(aq) + 5 Na. NO 2(aq) + 6 HCl(aq) 2 Mn. Cl 2(aq)+ 3 H 2 O(l)+ 5 Na. NO 3(aq) + 2 KCl 17

OH- Net: Cr. I 3 (s) + Cl 2 (g) Cr. O 42 -(aq)

OH- Net: Cr. I 3 (s) + Cl 2 (g) Cr. O 42 -(aq) + IO 4 -(aq) + Cl-(aq) Ox: [ 32 OH-(aq) + Cr. I 3(s) Cr. O 42 -(aq) + 3 IO 4 -(aq) + 16 H 2 O(l) + 27 e- ] 2 Red: [ 2 e- + Cl 2(g) 2 Cl-(aq) ] 27 Balanced net: 64 OH-(aq) + 2 Cr. I 3(s) + 27 Cl 2(g) 2 Cr. O 42 -(aq) + 6 IO 4 -(aq) + 54 Cl-(aq) + 32 H 2 O(l) 18

Exp 16: S 2 O 32 - (aq) thiosulfate ion Ox: Red: Balanced net:

Exp 16: S 2 O 32 - (aq) thiosulfate ion Ox: Red: Balanced net: + I 2 iodine S 4 O 62 -(aq) + I-(aq) 2 S 2 O 32 -(aq) S 4 O 62 -(aq) + 2 e- + I 2(aq) 2 I-(aq) 2 S 2 O 32 -(aq) + I 2(aq) S 4 O 62 -(aq) + 2 I-(aq) Outside exercise II page 199 – posted on my website

S 2 O 32 I 2 2 eq = 2 mol S 2 O

S 2 O 32 I 2 2 eq = 2 mol S 2 O 32 - 1 eq mol S 2 O 32 - 2 eq mol I 2 Exp today First: Standardize thiosulfate against 0. 100 N I 2 standard solution. Changes in sample preparation: 10 m. L I 2, 30 m. L deionized H 2 O, 1 m. L starch (20 drops) Starch – indicator (add from beginning) Starch + I 2 gives blue color At end pt (all I 2 consumed), solution will be colorless

Since using normality can use Niodine. Viodine = Nthiosulfate. V thiosulfate minimum 3 runs

Since using normality can use Niodine. Viodine = Nthiosulfate. V thiosulfate minimum 3 runs ± 0. 005 N (around ± 0. 5 m. L) report Avg N ± s N thiosulfate ion (S 2 O 32 -) Convert average N to M

Second: Same exact procedure as standardization except using unknown conc. of I 2. minimum

Second: Same exact procedure as standardization except using unknown conc. of I 2. minimum 3 runs ± 0. 005 N (around ± 0. 5 m. L) report Avg N ± s N iodine (I 2) unknown Convert average N to M

Amount of chemicals to obtain in small beaker per group: Na 2 S 2

Amount of chemicals to obtain in small beaker per group: Na 2 S 2 O 3. 5 H 2 O – 150 m. L (source of thiosulfate ions) 0. 100 N I 2 standard solution – 50 m. L Unknown I 2 solution – 45 m. L