Ch4
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Ch4 Presentation Transcript

  • 1. AQUEOUS REACTIONS & SOLUTION STOICHIOMETRY CHAPTER 4
  • 2. Ionic Compounds in Water
    • Electrolyte – they conduct electricity
    • They SEPARATE when they dissolve
      • NaCl  Na + + Cl -
    Water is POLAR, it has a charge difference from one side to another
  • 3.
    • They mostly don’t break apart, they disperse
    • No ions, no conductivity
    • Only polar compounds (have charge difference from one side to another) dissolve
    • SOME FEW molecules will break apart to form ions namely acids (HBr)
    Molecular Compounds in Water
  • 4.
    • Strong electrolytes are boring, they split apart (disassociate) and stay disassociated NaCl  Na + + Cl -
    • For Weak electrolytes, only some of the molecules will disassociate, the rest stay together
    • The strength of the electrolyte depends on the amount of molecules that break disassociate
    Strong & Weak Electrolytes
  • 5. Strong & Weak Electrolytes
    • Since weak electrolytes have both the capacity to disassociate AND reassociate after separating
    • Since there are 2 reactions (whole molecules to ions and ions to whole molecules) we write the equation to show that there are 2 reactions
    CH 3 COOH (aq) CH 3 OO - (aq) + H + (aq)
  • 6.
    • These reactions that occur both forwards and backwards are considered to be in CHEMICAL EQUILIBRIUM
    Strong & Weak Electrolytes
  • 7.
    • These are (surprise) reactions that form a precipitate
    • If a precipitate forms, there can be no equilibrium since the precipitate does not form ions and drops out of solution. The reaction can go forward, but can’t go backwards since some of the reactants have been inerted.
    Precipitation Reactions
  • 8.
    • Pb (NO 3 ) 2 (aq) + Na 2 (CrO 4 ) (aq) 
    • Pb (CrO 4 ) (s) + 2 NA(NO 3 )
    • Pb (CrO 4 ) is a solid and does not form ions, so there can be no reverse reaction.
    • See page 125 for a solubility guide
    Precipitation Reactions
  • 9.
    • NO 3 - All nitrates are soluble.
    • Cl- All chlorides are soluble except AgCl, HgCl 2 , and PbCl 2 .
    • (SO 4 )- Most sulfates are soluble. Exceptions include BaSO 4 , PbSO 4 , and SrSO 4 .
    • CO 3 - All carbonates are insoluble except NH 4 + and those of the Group 1 elements .
    • OH- All hydroxides are insoluble except those of the Group 1 elements, Ba(OH) 2 , and Sr(OH) 2 . Ca(OH) 2 is slightly soluble.
    • S 2 - All sulfides are insoluble except those of the Group 1 and Group 2 elements and NH 4 +.
    Solubility Rules
  • 10.
    • Predicting if strong electrolytes will form a precipitate
    • Ag(NO 3 ) (aq) + NaCl (aq)  ?
    Solubility Rules
  • 11.
    • Chlorides are soluble EXCEPT Ag, Hg, and Pb… so
    • Ag(NO 3 ) (aq) + NaCl (aq)  AgCl (s) + Na(NO 3 ) (aq)
    Solubility Rules
  • 12.
    • Acids are compounds that form positive Hydrogen ions H + when dissolved
    • Bases are compounds that form negative hydroxide ions OH - when dissolved
    • As you can easily guess one H + and one OH - combine to form H 2 O
    Acid - Base Reactions
  • 13.
    • Strength of acids and bases depend on the amount of material that disassociates
    • Much disassociation makes strong acids and bases
    • Little disassociation, weak acids and bases
    Acid - Base Reactions
  • 14.
    • NEUTRALIZATION
    • When acids and bases react with each other the H + and OH - ions combine
    • A solution that is not acidic or basic is said to be neutral. Why? Wait a few slides
    • Acids and bases react with each other to form water and a salt
    Acid - Base Reactions
  • 15. Acid - Base Reactions H + and OH - always react to form HOH or H 2 O The cation (metal from the base) reacts with the anion from the acid (everything after the H) to form the salt.
  • 16.
    • Watch the subscripts on the acids and bases
    • Acids have 1,2, or even 3 H + : bases 1 to many OH -
    • When balancing the equations, you must add enough acid or base to compensate and get an electrically neutral product
    • And you thought the term neutralize referred to canceling out the acid and base!
    Acid - Base Reactions
  • 17.
    • GAS FORMATION
    • Just like some reactions form solids, some form gases
    • If you have ever taken an antacid, or made the infamous “erupting volcano” science project in grade school, you have done a acid – base neutralization reaction with gas formation (so you can cross that off your bucket list)
    Acid - Base Reactions
  • 18. Acid - Base Reactions
    • The Volcano
  • 19.
    • Called redox reactions
    • Something is oxidized and something is reduced
    • The element or compound whose charge goes DOWN is REDUCED
    • The one whose charge goes up is oxidized
    Oxidation - Reduction Reactions
  • 20.
    • Atoms in elemental form 
      • oxidation number =0
    • For ions  oxidation number = charge
    • Metals have positive oxidation numbers, nonmetals have negative numbers
    • Hydrogen can act like a metal (HCL) or a nonmetal (NaH). It’s oxidation number is +1 if a metal, -1 if a nonmetal
    Oxidation - Reduction Reactions
  • 21. Oxidation - Reduction Reactions
    • Rust
    • Remember that reactions occur when elements transfer electrons to fill or deplete their outer electron shell
    O went from 0 to -2 so it was reduced Fe went from 0 to +3 so it was oxidized
  • 22. Oxidation - Reduction Reactions
    • Oxidation of metals by acid or salt – replacement (displacement) reactions
    • An ion in solution is replaced by the metal
    Hydrogen is reduced (+1 to 0) Sn is oxidized (0 to +2) The charges balance
  • 23. Oxidation - Reduction Reactions
    • Replacement of a metal by a salt
    • Cu went from a 0 to a +2, so it was oxidized
    • Ag went from +1 to 0, so it was reduced
    • (NO) 3 just sat back and watched (a spectator ion)
    • The charges ballance
  • 24. Oxidation - Reduction Reactions
    • Activity series of metals (p141)
    • A metal can only displace a metal that is LOWER on the chart
    • If the metal is higher on the chart, there is NO reaction
    Don’t memorize the series, if you need one for a test or quiz, I’ll provide one
  • 25.
    • Molarity (M) the ratio of moles of solute (the stuff that gets dissolved) and the volume of the solution in liters
    • 1 mole of HCl in 1 liter of water gives a 1M solution of HCl
    Concentration of Solutions
  • 26. Concentration of Solutions
  • 27. Concentration of Solutions
  • 28. Concentration of Solutions
  • 29.
    • I have two bottles of NaCl one is 233ml of 0.567M salt, the other 0.547ml of 4.23M salt. I mix them together. What is the Molarity of the final solution?
    • Sol 1: 233ml*0.567 mols/L*1L/1000ml = 0.132mol
    • Sol 2: 547ml*4.23mols/L*1L/1000ml = 2.38 mol
  • 30.
    • Sol 1 0.132mol 0.233L
    • Sol 2 2.38 mol 0.547 L
    • Total 2.45 mol 0.780 L
    • Molarity= 2.45 mol/0.780L=3.14M
  • 31.
    • Coefficients in chemical equations are ratios of moles (pieces) of reactants and products
    • Molarity is the amount of material (in moles) in a given amount of liquid
    • We can use concentration and volume to determine the number of moles of reactants either present (in the beaker) or that are needed (what we need to add to the beaker) for a reaction.
    Solution Stoichiometry
  • 32. Solution Stoichiometry Mass A Moles B Moles A Mass B Volume / Molarity A Volume / Molarity B Formula Weight Stoichiometry M=mol/L
  • 33. Solution Stoichiometry
    • How many grams of NaOH is needed to neutralize 75ml of 2 Molar H 2 SO 4 ?