Homework 1 Group Leader Member 1 Member 2 Member 3 Member 4 Member 5 Member 6 Environmental Chemistry CEE 330 3 3 3 6 3 7 and 3 9 and 3 11 Textbook 1 Reaction Stoichiometry 2 Reaction Stoichiometry In a closed system the number of atom of each element present remain constant Determine the stoichiometric coefficients for the following reaction aCH4 bO2 mCO2 nH2O A a 1 m 2 b 4 n 0 B a 1 m 1 n 2 b 2 C a 1 m 3 n 3 b 1 D None of the above 3 Combustion What mass in g of CO2 would be produce if 160 g of natural gas CH4 is completely oxidized to CO2 and H2O CH4 2O2 CO2 2H2O A B C D 4 CH4 2O2 CO2 2H2O 4 4g 44g 440g None of the above 5 6 1 Strong Acid Strong Base Reaction H2SO4 2NaOH H2SO4 H2SO4 2NaOH 2H2O Na2SO4 1 mole of H2SO4 will neutralize 2 moles of NaOH H HSO4 HSO4H SO4 2 40 mL of 0 5 M sulfuric acid neutralize 60 mL of NaOH What is concentration of NaOH A 1 M B 2 M C 0 67M D None of the above 2H2O Na2SO4 40 mL of 0 5 M sulfuric acid has 0 05 M x 0 04 L 0 02 moles 0 04 moles of NaOH will be neutralized Concentration of NaOH 0 04 moles 0 06L 0 67M 7 8 Ocean Acidification At reaction equilibrium A The rates of the forward and backward reaction are equal B The rate of the forward is a lot greater than the rate of the backward reaction C Nothing to do with rates D None of the above 9 10 http www pmel noaa gov co2 OA OA2 jpg Equilibrium processes need to be considered for ocean acidification 1 Air water equilibrium example 2 Acid base chemistry example 3 Precipitation dissolution example http www pmel noaa gov co2 OA OA1 jpg http www nsf gov news news images jsp cntn id 125523 org NSF 11 12 2 Examples Electroneutrality charge balance Water H2O H OHElectroneutrality for water H OH Table salt NaCl in water NaCl Na Cl and H2O H OHElectroneutrality for table salt NaCl in water H Na OH Cl The electroneutrality principle derived from stoichiometry states that an aqueous solution cannot possess a net electrical charge zC i i 0 where zi is the charge per molecule on the ith ion including a sign for cation and sign for anion Ci is the molar concentration of the ith ionic species 13 Examples 14 example CaCl2 in water CaCl2 Ca2 2Cl and H2O H OHElectroneutrality for CaCl2 in water H 2 Ca2 OH Cl Each Ca2 has 2 charges its charge contribution is twice as much per mole as H A sample of seawater is analyzed for ion content assume H and OH are much smaller than these ions Na 0 468M Mg 2 0 053M Ca 2 0 010M K 0 010M Cl 0 545M SO 4 2 0 028M HCO3 0 004M total cation charge Na 2 Mg 2 2 Ca 2 K 0 605 total anion charge Cl 2 SO 4 2 HCO3 0 605 15 16 Rainwater in pristine environment at 25 C and 1 atm total pressure contain the following species H HCO3 CO3 2 OH CO2aq Which of the following electroneutrality equation is correct A H OH HCO3 CO32 B H OH HCO3 2 CO32 17 18 3 Equilibrium processes need to be considered for ocean acidification Air water equilibrium Henry s law Aqueous CO2 is formed when atmospheric CO2 dissolves in water We can find its concentration in fresh water using Henry s law 1 Air water equilibrium example 2 Acid base chemistry example 3 Precipitation dissolution example CO2 gas CO2 aq KH CO2 aq 0 0334mol L atm Pg CO2 aq K H Pg 0 0334mol L atm 360 10 6 atm 1 2 10 5 mol L 19 20 Equilibrium processes need to be considered for ocean acidification Air water equilibrium Henry s law Henry s law is applied for all volatile chemicals oxygen in gas phase oxygen dissolved in water 1 Air water equilibrium example 2 Acid base chemistry example 3 Precipitation dissolution example O2 aq K H Pg 21 22 Acid Base Equilibrium constant Ka Acid base reaction HA H A H 2O H OH H A equilibrium constant Ka HA H OH K 10 14 w H 2O Convention in chemistry pKa logKa or Ka 10 Ka This equation must always be satisfied Log H pH or H 10 pH For neutral solutions H OH 10 7 or pH 7 0 For acidic solutions H OH and H 10 7 or pH 7 For basic solutions H OH and H 10 7 or pH 7 23 24 4 K a 10 4 76 The total number of positively charge per unit volume must equal to total number of negatively charge per unit volume The total number of positively negatively charge per unit volume molar concentration of each species time its charge Image that we have a room and there are boxes whose areas are charge x concentration concentration 25 H2O H OHAssume we have 1 M of H and 1 M of OH2Cl CaCl2 Assume we have 1 M of Ca2 and 2 M of Cl 2 1 M of Ca2 1 M of CO32 5 M of H 1 1 1 M of OH 2 M of Cl 1 1 1 M of H 2 M of HCO3 1 1 Ca2 1 M of OH 26 2 2 H CH 3COO H CH 3COOH CH 3COOH charge weak acid CH 3COOH H CH 3COO with pKa 4 76 Electroneutrality Principle for Aqueous Solution 27 In reality you do not know concentration of each species Instead you have to use electroneutrality principle and equilibrium constants to calculate these concentrations 28 aqueous CO2 reacts quickly with water Aqueous CO2 is formed when atmospheric CO2 dissolves in water concentration of aqueous CO2 can be found using Henry s law constant CO2aq KHP CO2 P CO2 is partial pressure of gaseous CO2 and equal to about 360 10 6 atm for clean air at total pressure of 1 atm KH 0 0334 Matm 1 CO2 0 0334 Matm 1 360 10 6 atm 1 2 10 5 M 29 Carbonic acid dissociation CO2 aq H 2O H HCO3 H HCO3 K1 4 47 10 7 mol L CO2 aq 30 5 Bicarbonate dissociation 1 2 10 5 M CO2 aqueous has now formed HCO3 H CO32 H CO32 K 2 4 68 10 11 mol L HCO3 A H OH CO32 B H OH CO32 HCO3 C OH CO32 HCO3 D None of the above Now we have 4 unknown We need to find 4 equations 31 2 CO2aq HCO3 3 32 2 CO32 CO2aq HCO3 3 log C 4 log C 4 CO32 5 5 6 6 7 7 pKa1 6 35 8 9 3 4 5 6 7 pKa1 10 33 8 9 9 10 11 12 13 14 3 pH 4 5 6 7 pKa1 …