Presentation on theme: "Aqueous solutions Types of reactions"— Presentation transcript:
1 Aqueous solutions Types of reactions Chapter 4Aqueous solutionsTypes of reactions
2 Parts of Solutions Solution- homogeneous mixture. Solute- what gets dissolved.Solvent- what does the dissolving.Soluble- can be dissolved.Miscible- liquids dissolve in each other.
3 Aqueous solutions Dissolved in water. Water is a good solvent because the molecules are polar.The oxygen atoms have a partial negative charge.The hydrogen atoms have a partial positive charge.The angle is 105º.
4 Hydration The process of breaking the ions of salts apart. Ions have charges and attract the opposite charges on the water molecules.
6 SolubilityHow much of a substance will dissolve in a given amount of water.Usually listed in g/100 mLSolubilities vary greatly, but if they do dissolve the ions are separated, and they can move around.Water can also dissolve non-ionic compounds if they have polar bonds.
7 Electrolytes Electricity is moving charges. The ions that are dissolved can move.Solutions of ionic compounds can conduct electricity and are therefore called “electrolytes.”
8 Types of solutions Solutions are classified three ways: Strong electrolytes- completely dissociate (fall apart into ions).Many ions- Conduct well.Weak electrolytes- Partially fall apart into ions.Few ions -Conduct electricity slightly.Non-electrolytes- Don’t fall apart.No ions- these sol’ns don’t conduct.
9 Types of solutions Acids- form H+ ions when dissolved. Strong acids fall apart completely.many ionsThere are just 6 strong acids – MEMORIZE THEM!Sulfuric acid: H2SO4Nitric acid: HNO3Hydrochloric acid: HClHydrobromic acid: HBrHydroiodic acid: HIPerchloric acid: HClO4Weak acids- don’t dissociate completely.
10 Types of solutions Bases - form OH- ions when dissolved. Strong bases- many ions. Most common:Lithium hydroxide: LiOH Sodium hydroxide: NaOH Potassium hydroxide: KOH Rubidium hydroxide: RbOH Calcium hydroxide: Ca(OH)2 Strontium hydroxide: Sr(OH)2 Barium hydroxide: Ba(OH)2
11 MOM to the rescue! Milk of magnesia = aqueous suspension of magnesium hydroxide Is Mg(OH)2 a strong base?Yes, technically… since all of the dissolved magnesium hydroxide dissociates.However, it has a very low solubility in water.
12 Measuring Solutions Concentration- how much is dissolved. 1 M = 1 mol solute / 1 liter solution
13 What is this???A one molar solution!!!Ha ha ha ha ha ha!1 L
14 Molarity Practice Problems Calculate the molarity of a solution with 34.6 g of NaCl dissolved in 125 mL of solution.How many grams of HCl would be required to make 50.0 mL of a 2.7 M solution?What would the concentration be if you used 27g of CaCl2 to make 500. mL of solution?What is the concentration of each ion?
15 Calculate the molarity of a solution with 34 Calculate the molarity of a solution with 34.6 g of NaCl dissolved in 125 mL of solution.
16 How many grams of HCl would be required to make 50. 0 mL of a 2 How many grams of HCl would be required to make 50.0 mL of a 2.7 M solution?
17 What would the concentration be if you used 27g of CaCl2 to make 500 What would the concentration be if you used 27g of CaCl2 to make 500. mL of solution? What is the concentration of each ion?Why?Because for everyone CaCl2 thereare two Cl- andone Ca2+… thus forevery 1 mol CaCl2,1 mole of Ca2+ and2 moles of Cl- form.[Ca2+]=0.49M[Cl-]=0.98M
18 Molarity Practice Problems Calculate the concentration of a solution made by dissolving 45.6 g of Fe2(SO4)3 to 475 mL.What is the concentration of each ion?This is because for every1 Fe2(SO4)3 particlethere are 2 iron ionsand 3 sulfate ions[Fe2+]=2(.240 M)=.480 M[SO42-]=3(.240 M)=.720 M
19 Practice Problems – Making Solutions Describe how to make mL of a 1.0 M K2Cr2O4 solution.Answer: Measure out 24 g of K2Cr2O4 in a volumetric flask. Add enoughdistilled water to dissolve the solid. Dilute to a total solution volume of mL.
20 Practice Problems – Making Solutions Describe how to make 250. mL of an 2.0 M copper (II) sulfate dihydrate solution.Answer: Measure out 98 g of CuSO4•2H2O in a volumetric flask. Add enoughdistilled water to dissolve the solid. Dilute to a total solution volume of 250. mL.
21 M1 V1 = M2 V2 Dilution Adding more solvent to a known solution. The moles of solute stay the same.M1 V1 = M2 V2Stock solution is a solution of known concentration used to make more dilute solutions
22 Dilution Practice Problems What volume of a 1.7 M solutions is needed to make 250 mL of a 0.50 M solution?M1V1 = M2V2(1.7 M)(V1) = (0.50 M)(250 mL)V1 = 74 mL
23 Dilution Practice Problems 18.5 mL of 2.3 M HCl is added to 250 mL of water. What is the concentration of the resulting solution?M1V1 = M2V2(2.3 M)(18.5 mL) = (M2)(250 mL+18.5 mL)M2 = 0.16 M
24 Dilution Practice Problems You have a 4.0 M stock solution. Describe how to make 1.0L of a .75 M solution.M1V1 = M2V2(4.0 M)(V1) = (0.75 M)(1.0 L)V1 = 0.19 L = 190 mLMeasure out 190 mL of 4.0 M stock solution.Dilute with enough water to make 1.0 L solution
25 Dilution Practice Problems 25 mL 0.67 M of H2SO4 is added to 35 mL of 0.40 M CaCl2 . What mass CaSO4 is formed?H2SO4 + CaCl2 CaSO4 + 2HCl
26 Dilution Practice Problems 25 mL 0.67 M of H2SO4 is added to 35 mL of 0.40 M CaCl2 . What mass CaSO4 is formed?LRH2SO4 + CaCl2 CaSO4 + 2HCl0.017mol0.014mol
27 Precipitation reactions Types of ReactionsPrecipitation reactionsWhen aqueous solutions of ionic compounds are poured together a solid forms.A solid that forms from mixed solutions is a precipitateIf you’re not a part of the solution, your part of the precipitate! LOL! :-D
31 Precipitations Reactions Only happen if one of the products is insolubleOtherwise all the ions stay in solution- nothing has happened.Need to memorize the rules for solubility!See Solubility Rules Handout!
32 Solubility Rules All nitrates are soluble Alkali metals ions and NH4+ ions are solubleHalides are soluble except Ag+, Pb+2, and Hg2+2Most sulfates are soluble, except Pb+2, Ba+2, Hg+2,and Ca+2Most hydroxides are slightly soluble (insoluble) except NaOH and KOHSulfides, carbonates, chromates, and phosphates are insolubleLower number rules supersede so Na2S is soluble
34 Three Types of Equations Molecular Equation- written as whole formulas, not the ions.K2CrO4(aq) + Ba(NO3)2(aq) ®BaCrO4(s) + 2KNO3(aq)Complete Ionic Equation shows dissolved electrolytes as the ions.2K+ + CrO4-2 + Ba NO3- ® BaCrO4(s) + 2K+ + 2 NO3-Spectator ions are those that don’t react.Net Ionic equation shows only those ions that react, not the spectator ionsBa+2 + CrO4-2 ® BaCrO4(s)
35 Practice ProblemWrite the three types of equations for the reactions when these solutions are mixed.iron (III) sulfate and potassium sulfidelead (II) nitrate and sulfuric acid
37 lead (II) nitrate and sulfuric acid Pb(NO3)2(aq) + H2SO4(aq) PbSO4(s) + 2HNO3(aq)Pb2+(aq) + 2NO3-(aq) + 2H+ + SO42-(aq) PbSO4(s) + 2H+(aq) + 2NO3-(aq)Pb2+(aq) + SO42-(aq) PbSO4(s)
38 Stoichiometry of Precipitation- Practice Problems Exactly the same, except you may have to figure out what the pieces are.What mass of solid is formed when mL of M barium chloride is mixed with mL of M sodium hydroxide?What volume of M HCl is needed to precipitate the silver from 50.ml of M silver nitrate solution ?
39 Stoichiometry of Precipitation- Practice Problems What mass of solid is formed when mL of M barium chloride is mixed with mL of M sodium hydroxide?BaCl2(aq) + 2NaOH(aq) Ba(OH)2(s) + 2NaCl(aq)0.01 mol0.01 molLR
40 Stoichiometry of Precipitation- Practice Problems What volume of M HCl is needed to precipitate the silver from 50.ml of M silver nitrate solution ?HCl(aq) + AgNO3(aq) HNO3(aq) + AgCl(s)? mLmol
41 Types of Reactions Acid-Base For our purposes an acid is a proton donor.a base is a proton acceptor usually OH-What is the net ionic equation for the reaction of HCl(aq) and KOH(aq)?Acid + Base ® salt + waterH+ + OH- ® H2O
42 Acid - Base ReactionsOften called a neutralization reaction Because the acid neutralizes the base.Often titrate to determine concentrations.Solution of known concentration (titrant) is added to the unknown (analyte) until the equivalence point is reached where enough titrant has been added to neutralize it.
43 or Titration Where the indicator changes color is the endpoint. Not always exactly at the equivalence point, but should pick an indicator that changes color very close to the endpoint.# of H+ x MA x VA = # of OH- x MB x VBorNA x VA = NB x VB
44 Titration Practice Problems A mL sample of aqueous Ca(OH)2 requires mL of M Nitric acid for neutralization. What is [Ca(OH)2 ]?NaVa = NbVb(0.0980N)(34.66mL)=(Nb)(50.00mL)Nb=NCa(OH)2=(M)(2)[Ca(OH)2]= M
45 Titration Practice Problems 75 mL of 0.25M HCl is mixed with 225 mL of M Ba(OH)2. What is the concentration of the excess H+ or OH-?[H+] = 0.25 M[OH-] = MExcess [OH-] = mol – mol = mol
46 Types of Reactions Oxidation-Reduction (“Redox”) Ionic compounds are formed through the transfer of electronsAn oxidation-reduction rxn involves the transfer of electronsWe need a way of keeping track – oxidation states
47 Oxidation States A way of keeping track of the electrons. Not necessarily true of what is in nature, but it works.need the rules for assigningmemorize these!
48 Rules for assigning oxidation states The oxidation state of an atom in an element is zero (i.e. Na(s), O2(g), O3(g), Hg(l))Oxidation state for monoatomic ions are the same as their charge. (i.e. Na+, Cl-)Oxygen is assigned an oxidation state of -2 in its covalent compounds except as a peroxide (such as H2O2).In compounds with nonmetals hydrogen is assigned the oxidation state +1.In its compounds fluorine is always –1.The sum of the oxidation states must be zero in compounds or equal the charge of the ion.
49 Oxidation States Practice Assign the oxidation states to each element in the following. CO2NO3-H2SO4Fe2O3Fe3O4+4-2+3-2+5-2-2+8/3-2+1+6-2
50 Oxidation-ReductionElectrons are transferred, so the oxidation states change.2Na + Cl2 ® 2NaClCH4 + 2O2 ® CO2 + 2H2OOIL RIGOxidation is the loss of electrons.Reduction is the gain of electrons.LEO GERLosing electrons - oxidationGaining electrons - reduction
51 Oxidation-ReductionOxidation means an increase in oxidation state - lose electrons.Reduction means a decrease in oxidation state - gain electrons.The substance that is oxidized is called the reducing agent.The substance that is reduced is called the oxidizing agent.