CHEM 200/202 Professor Jing Gu Office: EIS-210 All emails are to be sent to: chem200@mail.sdsu.edu My office hours will be held in GMCS-212 on Monday from 9 am to 11 am or by appointment.
ANNOUNCEMENTS Chapter 2 homework due 9/14/18 Lab report Volumetric Equipment and Pre-Lab assignment and report: Qualitative Analysis is due on 9/17/18 Quiz 1 due 9/20/18. Homework Chapter 3 and 4 due 9/21/18. Exam 1 is on 9/22/18 at 2-4 pm.
PPB CALCULATIONS The lead content of the tap water in Flint Michigan was found to be as high as 27 ppb. The EPA limit is 15 ppb, though levels above 5 ppb are a cause for concern. How many atoms of lead were in a 250. ml volume of Flint tap water at its worst? What was the molar concentration of lead in Flint s tap water at its worst?
SELECTED ACIDS & BASES Strong Acids Hydrochloric acid, HCl Hydrobromic acid, HBr Hydroiodic acid, HI Nitric acid, HNO3 Sulfuric acid, H2SO4 Perchloric acid, HClO4 Weak Acids Hydrofluoric acid, HF Phosphoric acid, H3PO4 Acetic acid, CH3COOH (or HC2H3O2) Strong Bases Sodium hydroxide, NaOH Potassium hydroxide, KOH Calcium hydroxide, Ca(OH)2 Strontium hydroxide, Sr(OH)2 Barium hydroxide, Ba(OH)2 Weak Bases Ammonia, NH3
ACIDS Monoprotic: one ionizable hydrogen HCl + H2O H3O + + Cl Diprotic: two ionizable hydrogens H2SO4 + H2O H3O + + HSO4 HSO4 + H2O H3O + + SO4 2 Triprotic: three ionizable hydrogens Polyprotic, generic term meaning that there is more than one ionizable hydrogen on the molecule. H3PO4 + H2O H3O + + H2PO4 H2PO4 + H2O H3O + + HPO4 2 HPO4 2 + H2O H3O + + PO4 3
BASES Monobasic: yields one OH - ion KOH K + + OH NH3 +H2O NH4 + + OH Dibasic: yields two OH ions Ba(OH)2 Ba 2+ + 2OH Ca(OH)2 Ca 2+ + 2OH
ACID-BASE NEUTRALIZATION Molecular equation Acid + Base Water + Salt Total ionic equation HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) H + (aq) + Cl (aq) + Na + (aq) + OH (aq) H2O(l) + Na + (aq) + Cl (aq) Net ionic equation H + (aq) + OH (aq) H2O(l) Hint: Balance the H + with OH - the rest will work itself out.
AN AQUEOUS STRONG ACID-BASE REACTION ON THE ATOMIC SCALE
QUESTION What is the concentration of a sulfuric acid solution if it requires 26.05 ml of a 2.045 M sodium hydroxide solution to titrate 12.05 ml of the sulfuric acid solution?
GAS FORMATION WITH AN ACID-BASE Molecular equation REACTION NaHCO3(aq) + CH3CO2H(aq) H2O(l) + CH3CO2Na(aq) + CO2(g) Total ionic equation Na + (aq) + HCO3 - (aq) + H + (aq) + CH3CO2 - (aq) H2O(l) + Na + (aq) + CH3CO2 - (aq) + CO2(g) Net ionic equation HCO3 - (aq) + CH3CO2H(aq) CH3CO2 - + H2O(l) + CO2(g)
An aqueous solution of H2SO4 is added to an aqueous solution of Ba(OH)2. The reaction is monitored using a conductivity meter. Predict the correct statement(s): 1. Both H2SO4 & Ba(OH)2 are strong electrolytes 2. This is a neutralization reaction 3. This is a precipitation reaction 4. The light bulb will glow at the neutralization point Answers A B C D E Statement 2 Statements 1 & 2 Statements 1, 2 & 3 All of the statements are true All of the statements are lies
Soluble SOLUBILITY RULES 1. All common compounds of Group 1A(1) ions (Li +, Na +, K +...) and ammonium ions (NH4 + ) 2. All common nitrates (NO3 - ), acetates (CH3CO2 - ) and most perchlorates (ClO4 - ) 3. All common chlorides (Cl - ), bromides (Br - ) and iodides (I - ); except those of Ag +, Pb 2+, Cu + and Hg2 2+. All common fluorides (F - ) are soluble; except for Pb 2+ & Group2A(2) 4. All common sulfates (SO4 2- ); except Ca 2+, Sr 2+, Ba 2+, Ag + & Pb 2+
LECTURE OBJECTIVES Chapter 4.2-4.4 Determine the oxidation states of elements in compounds. Identify the oxidizing and reducing agents in redox reactions. Perform stoichiometric calculations involving mass, moles, and solution molarity. Calculate theoretical, and percent yields for chemical reactions.
REDOX REACTIONS IN COMPOUND FORMATION Electrons are transferred in the formation of ionic compounds. Electrons are shifted in the formation of covalent compounds.
1. For Group 1(A)1 - O.N. is +1 in all compounds 2. For Group 2(A)2 - O.N. is +2 in all compounds 3. For hydrogen - O.N. is +1 when bound to nonmetals 4. For fluorine - O.N. is -1 when bound to metals & boron 5. For oxygen - O.N. is -1 when in peroxides (e.g. H2O2) - O.N. is -2 for all others (except with fluorine) 6. For Group 7(A)17 - O.N. is -1 when with metals, nonmetals (except O) & for other halogens lower in group OXIDATION NUMBER RULES General Rules 1. For an atom in its elemental form (e.g. Na, O2, Cl2,...) the O.N. = 0. 2. For a monoatomic ion (e.g. Br -, Cu 2+,...) the O.N. = ion charge. 3. The sum of the O.N. values for atoms in a compound equals zero. For polyatomic ions the sum equals the charge of the ion. Specific Rules
OXIDATION NUMBERS The main group elements can have different oxidation numbers depending on the molecule they are part of. Compound O.N. of nitrogen NH3-3 N2H4-2 NH2OH -1 N2 0 N2O +1 NO +2 NO2 - +3 NO2 +4 NO3 - +5
REDOX TERMINOLOGY 2Mg(s) + O2(g) 2MgO(s) 2Mg 2Mg 2+ + 4e - O2 + 4e - 2O 2- O.N.: 0 +2 O.N.: 0-2 Mg loses electrons Mg is oxidized Mg is the reducing agent The oxidation number of Mg is increased O gains electrons O is reduced O is the oxidizing agent The oxidation number of O is decreased
OXIDATION REDUCTION OIL RIG Oxidation is loss of electrons Reduction is gain of electrons LEO GER Lose electrons is oxidation Gain electrons is reduction
QUESTION What is the oxidation number of carbon in Na2C2O4? Oxidation number: 0 +1 +2 +3 +4
QUESTION Identify the oxidizing agent and reducing agent in the following reaction: Sn(s) + 2H + (aq) Sn 2+ (aq) + H2(g) Oxidizing agent Reducing agent Answer H + Sn A H + Sn 2+ B Sn H + C Sn H2 D Sn 2+ H2 E
TYPES OF REDOX REACTIONS The different types of redox reactions are classified by the components of the reaction and what happens to those components. There are four types of redox reactions which involve elements - combination, decomposition, displacement and combustion. In these reactions, elements may be reagents, products or transferred during the reaction.
COMBINATION REACTION 2K(s) + Cl2(g) 2KCl(s) 2NO(g) + O2(g) 2NO2(g)
DECOMPOSITION REACTION 2H2O(l) 2HgO(s) 2Hg(l) + O2(g) electricity 2H2(g) + O2(g) = heat
DISPLACEMENT REACTION An active metal displacing hydrogen from water 2Li(s) + 2H2O(l) 2LiOH(aq) + H2(g)
COMBUSTION REACTIONS Combustion reactions always involve elemental oxygen. The reactions reduce oxygen and release energy, frequently as heat and light. 2CO(g) + 2O2(g) 2CO2(g) 2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g) C6H12O6(g) + 6O2(g) 6CO2(g) + 6H2O(g)
REACTION YIELDS The reaction yield is a measure of the completeness of a reaction; quantifying how much of the possible product was formed. Determining the theoretical yield for a reaction requires a balanced chemical reaction, and the identification of the limiting reagent. The limiting reagent is the reagent that will be entirely consumed first, stoping the reaction (limiting the amount of product formed).
LIMITING REAGENT The Haber-Bosch process produces ammonia from nitrogen and hydrogen gas (unbalanced reaction below). _N2(g) + _H2(g) _NH3(g) Hydrogen limiting reagent: How many grams of ammonia would be produced if you 3.00 mol of H2 and an infinite amount of N2? Nitrogen limiting reagent:how many grams of ammonia would be produced if you 3.00 mol of N2 and an infinite amount of H2?
PROBLEM Considering this reaction: _N2(g) + _H2(g) _NH3(g) If 1.83 mol of N2 is reacted with 5.92 mol of H2, how many grams of NH3 will be produced? How many moles of the non-limiting (excess) reagent, are left over after the reaction? What mass of each gas will you have once the reaction is completed?
REACTION YIELDS Not every reaction proceeds perfectly to produce 100% of the maximum product. Reactions that are imperfect has reaction yields of less than 100%. Considering the reaction: _N2(g) + _H2(g) _NH3(g) The reaction is performed with 1.84 mol of N2 and 2.84 mol of H2. At the end of the reaction you collect 0.932 mol of NH3. What is the yield of this reaction?
PROBLEMS 8.09 g of H2 react with 4.82 g of N2. The reaction has a 72.5% yield. What mass of NH3 is produced?( Do it together) 45.92 g of N2 is reacted with an excess of H2. The reaction produces 36.05 g of NH3. What is the yield of this reaction? How much mass of N2 was left unreacted? (Do it by yourself)
QUANTITATIVE ANALYSES Knowledge of the stoichiometry of a reaction, along with the composition and amount of one of the reagents, we can quantify the other component in the reactions. This is the basis of titrations, where carefully measured amounts of a reagent (e.g. a base) is added to a solution of unknown composition to quantify the amount of a reagent (e.g. an acid).
PROBLEM You have 4.912 g of a solid mixture. The mixture is known to contain both NaCl, and NaOH. You dissolve all the solid in 50.00 ml of water. (Do it together) You titrate the solution with HCl, to neutralize the NaOH, while not reacting with the NaCl. You need 32.67 ml of 0.5638 M HCl to neutralize the solution. What percentage of the solid was NaOH?
PROBLEM A 25.00 ml solution contains an unknown amount of Pb(NO3)2. An excess of aqueous KI is added to the solution, precipitating all the lead as lead(ii) iodide. The amount of lead(ii) iodide is determined to be 1.042 g. What was the concentration of Pb(NO3)2 in the original 25 ml solution?( Do it by yourself)