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Ch.4 Chemical Rxns and Solution Stoichiometry 4.1 Water.

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Presentation on theme: "Ch.4 Chemical Rxns and Solution Stoichiometry 4.1 Water."— Presentation transcript:

1 Ch.4 Chemical Rxns and Solution Stoichiometry 4.1 Water

2 I. H 2 O Structure A. Polar Covalent bonds between O and H B. Unequally shared e - s, more by O C. Oxygen gets slightly negative charge, Hydrogen slightly positive D. “Polar” molecule: negative end and positive end

3 II. Hydration A. Process of water separating ions NaCl (s)  Na + (aq) + Cl - (aq) B. Aqueous (aq): means dissolved in water C. Cations attracted to Oxygen in water D. Anions attracted to Hydrogen in water E. Dissolving: ions surrounded by water molecules or uncharged atoms surrounded by water

4 F. Like dissolves like: polar molecules, ions, dissolved by water G. Non-polar (ex. Oil) dissolved by other non-polar molecules

5 4.2: I. Strong/ Weak Electrolytes A. Solute: particles that are dissolved B. Solvent: dissolving agent C. Electrolytes: ionic compounds that break into ions allowing passage of electrons (electricity) E. Strong: conduct lots of electricity, fully break into ions F. Weak: not good conductors, don’t break apart easily

6 II. Arrhenius C. Strong bases (contain OH - ), completely break into ions in solution HCl (aq) + NaOH (aq)  NaCl (s)+ H 2 O (l) 100% A. Defined “Acid”: produces protons (H + ) when dissolved in water B. HCl, HNO 3, H 2 SO 4, HBr, HI, HClO 4 : strong acids, completely break into ions (MEMORIZE THESE!)

7 III. Weak Electrolytes HC 2 H 3 O 2 (aq)  H + (aq) + C 2 H 3 O 2 - (aq) 99% 1% 1% Weak Acid NH 3 (aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq) 99% 99% 1% 1% Weak Base A. Non-electrolytes: do not become ions at all, ex. Ethanol, sucrose; but can still be dissolved

8 4.3: I. Composition of Solutions A. Use molarity to measure solution concentration Molarity (M) = moles of solute/L of solution B. Units are written as M or as moles/L C. Dilution: reducing concentration by adding water (or more solvent) to a solution **Moles of solute does not change with dilution**

9 II. Dilution Calculation B. Molarity = moles/volume C. M 1 x Volume 1 = Moles = M 2 x Volume 2 D. M 1 V 1 = M 2 V 2 1. Use MV=MV calculation to determine how many liters of a stock solution will give us the moles we need to make desired Molarity 2. Make up the remainder of the missing volume with distilled water A. To dilute a certain concentration solution to a lesser concentration

10 4.5: I. Precipitation Rxns A. When two solutions are mixed, sometimes insoluble products are made (“Precipitates”) Ex. KI (aq) + Pb(NO 3 ) 2 (aq)  PbI 2 (s) + KNO 3 (aq) B. Also called “double replacement” rxns because two ions are switching places C. Need to be able to predict the products and their likely states

11 II. Determining Precipitates A. If we mix KOH and Fe(NO 3 ) 3 what do we form? Ex. KOH (aq) + Fe(NO 3 ) 3 (aq)  _____ + _____ B. A reddish precipitate is formed, how do we know which product it is? C. There are general solubility trends that we can use to reasonably predict

12 III. Solubility Rules A. Always Soluble: Alkali metals (1 st column), NH 4 +, NO 3 -, ClO 3 -, ClO 4 -, C 2 H 3 O 2 - B. Mostly Soluble:Cl -, Br -, I - (except Ag +, Pb 2+, Hg 2 2+ ) C. F - (except Ca 2+, Ba 2+, Sr 2+, Pb 2+, Mg 2+ ) D. SO 4 2- (except Ca 2+, Ba 2+, Sr 2+, Pb 2+ ) E. Mostly Insoluble: O 2-, OH -,CO 3 2-, PO 4 3-, S 2-, SO 3 2-, C 2 O 4 2-, CrO 4 2- (except w/ soluble cation)

13 4.6: I. Reactions in Solutions A. Balanced Molecular equation K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq)  BaCrO 4 (s) + 2 KNO 3 (aq) B. Complete Ionic equation: separate aqueous into ions 2K + + CrO 4 2- + Ba 2+ + 2NO 3 -  BaCrO 4 (s) + 2K + + 2NO 3 - C. Net Ionic equation: get rid of “Spectator Ions”, not participating in reaction CrO 4 2- (aq) + Ba 2+ (aq)  BaCrO 4 (s)

14 4.7: I. Precipitation Rxn Stoichiometry 1. Start with net ionic equation 2. Since we’re dealing with solutions we are given Molarity of reactants instead of grams 3. Use Molarity to convert to moles 4. Other steps are the same

15 4.8: I. Acid – Base Rxns A. Bronsted- Lowry defined acid as a proton donor B. Base: proton acceptor HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) C. Net ionic: H + (aq) + OH - (aq)  H 2 O (l) D. A strong acid and a strong base neutralize each other to a salt and water KOH (aq) + HC 2 H 3 O 2 (aq)  KC 2 H 3 O 2 (aq) + H 2 O (l)

16 F. Net Ionic: OH - (aq) + HC 2 H 3 O 2 (aq)  C 2 H 3 O 2 - (aq) + H 2 O (l) Since weak acid, doesn’t dissociate well in water (“aqueous”) G. Acid Base rxns often called “Neutralization Rxns” because of formation of water E. Strong Base + Weak Acid: Weak acid can’t lose all H +, but base is strong enough to rip off Proton from Acetic Acid

17 II. Titrations A. Measured volume of known concentration (“Titrant”) into unknown substance (“Analyte”) to react equally B. Acid base titration: exact amount of acid and base neutralize each other (“equivalence point”) C. Indicator changes color to signal end of reaction (“End point”) D. Oxidation/Reduction titration: use oxidizing agent (takes electrons) and reducing agent (loses electrons) in equal quantities to reach “End point”

18 4.9: I. Oxidation-Reduction Rxns A. Also called REDOX B. Involve electrons being transferred C. To determine if electrons are being transferred in a reaction, need to look at charges and see if and how they change D. For covalent (non-charged) compounds, we assign artificial charges called “Oxidation #’s”

19 II. Oxidation # Rules 1. Atoms by themselves or attached to identical atoms always 0 2. An ion charge = its oxidation # 3. Oxygen is -2 except in peroxides (-1) 4. Hydrogen is +1, except in metal hydrides (-1) 5. Sum of the ox. #’s of a neutral compound must equal zero

20 III. REDOX Rxn Information A. Always have one element that is oxidized and one element that is reduced B. Oxidation: Losing electrons C. Reduction: Gaining electrons D. Oxidized molecule (“reducing agent”), reduced molecule (“oxidizing agent”) LEO

21 4.10: I. Balancing REDOX Rxns: Half-Rxn Method for Acidic Solutions A. For hard to balance Acid-Base Rxns 1. Assign oxidation #’s to complete ionic eqn. 2. Make half-rxns of just the molecules before and after that are being oxidized or reduced 3. Balance all elements in half rxns except H, O 4. Balance O using H 2 O 5. Balance H using H + 6. Balance charges using electrons 7. Combine half-rxns and cancel out repeats

22 1. Balance like an acidic solution 2. To both sides of rxn, add OH - equal to number of H + 3. Make equal H + and OH - into water and cancel other waters out Half-Rxn Method for Basic Solutions II. Balancing:

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