Notes - Chapter 4a
Notes - Chapter 4a CHEM-UA 125
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This page Class Notes was uploaded by an elite notetaker on Tuesday February 23, 2016. The Class Notes belongs to CHEM-UA 125 at NYU School of Medicine taught by Dr. Malgorzata (Margaret) Mandziuk in Spring 2016. Since its upload, it has received 33 views. For similar materials see General Chemistry I in Chemistry at NYU School of Medicine.
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Date Created: 02/23/16
Chapter 4 THREE MAJOR CLASSES OF CHEMICAL REACTIONS AQUEOUS SOLUTIONS Homogeneous Solution Preparation of Solution WILL be on exam Solid or Liquid Alvariable compositioniof a solution may bezexpressed in terms of mass percents example Hydrogen peroxide commonly available in drug stores is a 3 solution of H202 in water Solute Solvent However in most cases solute is present in much smaller quantity than the solvent It isimore convenient to express composition as a concentration of solutes in a solution example RinhiinSil i Robitussin BM contains 10 mg of Dextromethorphan HBr 7 and 100 mg of Guaifenesin in 5 mL tsp of syrup SOLUTION homogeneous mixturx SOLVENT SOLUTES the substance present in theigreater amount the substance dissolved in the solvent We can have solutions of o a solid in a liquid o a li uid in a li uid q q I Not Very Important Skipped over in class o a gas in a liquid O a solid in a solid alloy 0 a gas in a gas 0 a gas in a solid MOLARITY o a chemist s way to define the concentration of an aqueous solution 0 gives thenumber of solute particles expressed in moles in one liter of the solution moles of solute Molarity Liters of solution I l IVI Not Given on Exam Memorizel V Molarity unit M quotTO 1L1000mL solute denotesmolarity of a solute eg to express that the molarity of a sodium chloride solution is 0311M we write Nacu 0311 M To express Molarity use brackets around solute example How would you prepare H 1quot Concentration of Moles does not change i 391 1 itric add Starting With When Dilutingonly add solvent 3 5 w 2 W1 fill Ml 3 a Molarity of Diluted solutionnitric acid to a given solution only water IS added MUCH smaller than stock solution m n f l r i l i n h n 39 a ou t 0 so ute pa tces s u c a ged subscript d quotHAOdd Vd X Md so diluted solution 2 1 L mol 500gtlt10 mL gtlt gtlt175 103 mL L moles of solute moles of solute 0875 mol In diluted from concentrated I Find moles of diluted solution solution solution Subscript c n n quotdiut quotcom concentrated solution HNO3 d HNO3 C I Moles of diluted solution is equal to concentrated solution quotHNO3 c 0875 mol V 010163L Mdiut X Vdiut Mconc X Vconc C MC M Molarity Volume of Diluted solution Molarity Volume of concentrated solution 102 L m Use Molarity of nitric acid as a Molarity of stock solution to find volume S O L U BI L I I Solids dissolve better in hot temp of a substance is the amount of that substance that can be dissolved in a given quantity of solvent at a specified temperature Water as a solvent Water is a dipole has both poitive and negative charges 5 a B Electron charge distribution is asymmetrical a bl C Concentrated solution Take a little from Dilute with water solute Dark blue concentrated solution C Each O H bond is polar example What is the molarity of calcium and hydroxide ions in M SOlUthh Does the concentration depend on the amount of solution 0015 M l take 1 L 0015 mol l 1CaOH2aq 1Ca2aq l 2OHaq 0015 mol 0030 mol l inlL l inlL 00015 M 00030 M ACIDS Arrhenius definition substances that in aqueous solutions produce hydrogen ions H for now molecular substances that IONIZE in aqueous solutions releasing hydrogen ions H p example HClaq gt Haq CI aq more generally acids are PROTON DONORS HClaq H20I gt H3Oaq CI aq STOICHIOMETRY OF A REACTION IN SOLUTION example How many grams of chloride ion are in the sample if 202 mL of 0100 M Agaq is required to react with all of the chloride The quantity of Claq in a water sample is determined by titrating with Agaq 202 mL 0100 M 3 202 X 1 mol O Agaq Claq AgCls 202 x 103 mol 1 00716 g m 202 x 10 3 x 0071609g 00716g Cl ar 391 quotLquot 13 I 0 a 3 is outlined a quot i 39H30 l A gt H from acid 39 7 V gt gt I from prof Mark E Tuckerman group s publication NAMES AND FORMULAS OF ACIDS Pattern of the relation between names of anions and their corresponding acids anion corresponding acid 9 taste sour formula name formula name 0 turn blue litmus paper red Cl chloride HCI hydrochloric aCId 2 o react with some metals to yield H2g S sulfide H25 hydrosulfurlc aCId 0 react with carbonates to yield C02g N03 nitrate HNO3 nitric acid N02 nitrite HN02 nitrous acid strong acids acids that ionize completely in an aqueous solution ClO perchlorate HClO4 perCthFiC aCICl complete ionization is represented by gt ClO chlorate HCIO chloric acid example 3 3 HCO4aq gt Haq CIOaq CIO chlorite HC02 chlorous acid ClO hypochlorite HCIO hypochlorous acid weak acids acids for which only a small fraction of the molecules are lonizable protons in inorganic acids are written at the beginning of the ionized in water at any given moment formula the double arrow indicates that changes occur simultaneously in H2504 HF both directions forward and reverse Species on both sides of the equation are in chemical dynamic equilibrium monoprotic acids HNO3 HCI CH3COOH diprotic acids H2504 H2CrO4 triprotic acids H3PO4 citric acid examples HFaq Haq F aq A CH3COOHaq H 37 CH3COO aq Ionization of a polyprotic acid is represented in stages Each stage represents an ionization of one proton Chemical equilibrium For sulfuric aCId there are two stages 0 No change on macroscopic scale concentration of ions and molecules constant in time 0 Change on microscopic scale H2SO4aq gt l laq HSOzHaq molecules constantly break into ions and then reform the reaction occurs in both directions HSOaq Haq SOiaq WEAK does not imply unreactive BASES Arrhenius definition substances that produce hydroxide ions when dissolved in water example NaOHaq gt Naaq OHaq more generally PROTON ACCEPTORS o taste bitter o feel slippery a turn red litmus paper blue Memorize the strong acids and strong bases in Table 42 Strong and Weak Table 42 Acids and Bases Acids Strong Hydrochloric acid HCl Hydrobromic acid HlBr Hydriodic acid HI Nitric acid IINO3 Sulfuric acid H2504 Perchloric acid HClO4 Weak a few of many examples Hydro uon39c acid HF Phosphoric acid H3PO4 Acetic acid or HC2H302 Bases Strong Group 1AI hydroxides Lithium hydroxide LiOH Sodium hydroxide NaOH Potassium hydroxide KOH Rubidium hydroxide RbOH Cesium hydroxide CSOH Heavy Group 2A2 hydroxides Calcium hydroxide CaOH2 Strontium hydroxide SrOH2 Barium hydroxide BaOH2 Weak one of many examples Ammonia NH3 Common bases 0 strong bases completely dissociate into ions in an aqueous solution 9 Water soluble metal hydroxides CaOH2s gt Ca2aq 20Haq 0 or oxides K20s H20l gt Kaq 20Haq The oxide ion is unstable in water O2aq l H20l gt 2 OHaq 0 weak bases partially ionize in an aqueous solution 0 Ammonia and its derivatives amines Caution presence of an OH group in a formula does not guarantee that the substance is basic eg alcohols phenols VitC ascorbic acid all have OH groups but they are not basic ELECTROLYTES substances whose aqueous solutions conduct electricity must contain ions strong electrolytes soluble ionic solids or molecular compounds that completely or nearly completely ionize in water weak electrolytes molecular compounds some acids and bases for which only a small fraction of the molecules are ionized in water at any given moment NONELECTROLYTES substances whose aqueous solutions do not conduct electricity contain negligible amount of ions most molecular compounds P a f s 39 39 3 39 quot I p aquot H A 2quot 39 H 39 faucets 709 ME Compounds 3 Wanna 53 quotgets 7 9 9 iquotquot39 J 393 5quot 51quot Jen sift53v Soluble Ionic Compounds Hand out given in class 039 e a n A Insoluble Exceptions All common compounds of Group lAl ions Li Naquot K etc None All common compounds of ammonium ion NI14 None None All common nitrates N03 acetates CH3COO39 or C2H302quot and perchlorates ClOf All common chlorides Cl bromides Br and iodides I39 All common uorides F All common sulfates 803 Insoluble Ionic Compounds All common metal hydroxides All common carbonates COf39 and phosphates POf All common sul des Chlorides bromides and iodides of Agi Pb Cu and Hg PbFz and uorides of Group 2A2 CaSO4 350 13130 Ag2804 PbSO Soluble Exceptions GroupiAu hydroxides an CaOH2 SrOH2 and BaOH2 Carbonates and phosphates of Group 1A1 and NH4quot Sul des of Group 1Al Group 2A2 and NH i I I39 t quot 39v3939 3 0quot quotquot 5739 3 s Tame 44 154 3 Rules for Asmgning an Oxidation Numberlp a General Rules 1 For an atom in its elemental form N a 02 C12 etc ON 0 2 For a monatomic ion ON ion charge with the sign before the numeral 3 The sum of ON values for the atoms in a molecule or fommla unit of a compound equals zero The sum of ON values for the atoms in a polyatomic ion equals the ion s charge Rules for Specific Atoms or Periodic Table Groups 1 For Group 1Al ON 1 in all compounds 2 For Group 2A2 ON 2 in all compounds 3 For hydrogen ON 1 in combination with nonmetals ON l in combination with metals and boron 4 For uorine ON 1 in all compounds 5 For oxygen ON 1 in peroxides ON 39 2 in all other compounds except with F 6 For Group 7A17I ON 1 in combination with metals nonmetals except 0 and other halogens lower in the group Most active metal strongest reducing agent quot Li K Ba Ce Na 0 O v 5 w 833 2H20I Ba2laq 20H39aq H2g Can displace H2 also see Figure 421 from water 39 quot H v ms 2H209 A 2n0H2ltsgt Hoe Can dispIace H2 39 from steam 39 Me Al Mn Zn Cr Fe Cd Co Ni Can diaplace H2 31 from acid P33 tj Cu H9 Cannot displace H2 Ag from any source AU l Sue 2H39aq gt Snz aq Hztg also see Figure 422 Strength as reducing agent j Ags 2Haq gt no reaction 0 Least active metal weakest reducing agent
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