Announcements 1. Limiting Reactants lab write-up due tomorrow at start of discussion. 2. Online HW 5 (Type I) due Monday 10/22 and (Type II) due Wednesday 10/24 by 7:00pm. 3. Stoichiometry workshop next Thurs. Must be present to get grade!
Molar mass mass Ideal gas law # particles Avogadro s # MOLES volume Gas properties (P,V,T) concentration
Remember, in a balanced equation, the coefficients represent: ratio of the number of particles (molecules or ions) OR a ratio of the number of moles needed Moles are our link with chemical equations!
Aqueous solutions (Molarity, volume) Moles of ions Aqueous solutions (Molarity, volume) Gases (P,V,T) Moles reactant A Moles reactant B Etc Moles product X Moles product Y Etc A + 2B + 3X + Y + Gases (P,V,T) Coefficient RATIOS Limiting reactant Coefficient RATIOS Masses (grams) Masses (grams)
Need to use balanced equation to determine ratios of reactants and products Example: N 2 (g) + 3H 2 (g) 2NH 3 (g) For every mole of N 2, need 3 moles of H 2 to make 2 moles of NH 3
How many moles of product is formed from each of the following given amounts of reactants? N 2 (g) + 3H 2 (g) 2NH 3 (g) A) 3 moles of N 2 and 3 moles of H 2 B) 1 mole of N 2 and 6 moles of H 2 C) 1 mole of N 2 and 3 moles of H 2 D) 1 mole of N 2 and 2 moles of H 2
How many moles of product is formed from each of the following given amounts of reactants? N 2 (g) + 3H 2 (g) 2NH 3 (g) A) 3 moles of N 2 and 3 moles of H 2
How many moles of product is formed from each of the following given amounts of reactants? N 2 (g) + 3H 2 (g) 2NH 3 (g) B) 1 mole of N 2 and 6 moles of H 2
How many moles of product is formed from each of the following given amounts of reactants? N 2 (g) + 3H 2 (g) 2NH 3 (g) C) 1 mole of N 2 and 3 moles of H 2
How many moles of product is formed from each of the following given amounts of reactants? N 2 (g) + 3H 2 (g) 2NH 3 (g) D) 1 mole of N 2 and 2 moles of H 2 How many moles of H 2 do I need to completely react with 1 mole of N 2?
How many moles of product is formed from each of the following given amounts of reactants? N 2 (g) + 3H 2 (g) 2NH 3 (g) D) 1 mole of N 2 and 2 moles of H 2 I would need 3 moles of H 2, but I only have 2 moles, so H 2 is limiting reactant
How many moles of product is formed from each of the following given amounts of reactants? N 2 (g) + 3H 2 (g) 2NH 3 (g) D) 1 mole of N 2 and 2 moles of H 2 2 moles H 2 * 2 moles NH 3 = 1.33 moles NH 3 3 moles H 2
Example DEMO: Magnesium CO 2 lantern Video link CO 2 reacts with a lot of metals (such as Mg) which is why using CO 2 fire extinguishers is a bad idea for putting out fires involving metals (because it won t put it out!) Sand works best in these situations.
Reaction forms magnesium oxide and carbon Formula of magnesium oxide: Mg 2+ and O 2- so formula is MgO Unbalanced equation: Mg(s) + CO 2 (g) -> MgO(s) + C(s)
Clicker #1 What is the sum of the coefficients for this equation in standard form? Mg(s) + CO 2 (g) -> MgO(s) + C(s) A) 4 B) 5 C) 6 D) 8
Unbalanced equation: Mg(s) + CO 2 (g) -> MgO(s) + C(s) Balanced equation: 2Mg(s) + CO 2 (g) -> 2MgO(s) + C(s)
Example Assume you have 5.00 g of Mg and 10.0 g of CO 2 available. You allow them to react. Prove that mass has been conserved. But before calculating
Clicker #2 What should be the total mass present after the reaction is complete? A) 1.24 g B) 5.00 g C) 9.54 g D) 10.0 g E) 15.0 g
Solution Stoichiometry Example: Ba(NO 3 ) 2 (aq) + Na 2 SO 4 (aq) -> BaSO 4 (s) + 2NaNO 3 (aq) You mix 1.0L of a 4.0M barium sulfate solution with 1.0L of a 3.0M sodium sulfate solution. What would be the mass of the solid that forms after the reaction is complete? What would be the concentration of each ion still left in solution after the reaction is complete?
What would be the concentration of each ion still left in solution after the reaction is complete? First, need to figure out which ions will be left in solution (spectator ions)
Molecular equation: Ba(NO 3 ) 2 (aq) + Na 2 SO 4 (aq) -> BaSO 4 (s) + 2NaNO 3 (aq) Complete ionic equation: Ba 2+ (aq) + 2NO 3- (aq) + 2Na + (aq) + SO 4 2- (aq) -> BaSO 4 (s) + 2Na + (aq) + 2NO 3- (aq) Net ionic equation: Ba 2+ (aq) + SO 4 2- (aq) -> BaSO 4 (s)
How many moles of each ion did we start with and how many are left? Remember that we started with 4.0 moles of Ba(NO 3 ) 2 and 3.0 moles of Na 2 SO 4
Clicker #3 What ions are left in solution after the reaction is complete? I. Ba 2+ II. NO 3 III. Na + IV. SO 4 2 A) I and II B) III and IV C) I, II and III D) I, II, and IV E) No ions are left in solution after the reaction is complete.
Final volume is 1.0L + 1.0L = 2.0L Ba 2+ (aq) NO 3- (aq) Na + (aq) SO 4 2- (aq) Starting moles 4 moles 8 moles 6 moles 3 moles Moles used 3 moles 0 moles 0 moles 3 moles Moles left 1 mole 8 moles 6 moles 0 moles So concentration of remaining ions: Ba 2+ : 1 mole/2.0l = 0.5M Ba 2+ Na + : 6 moles/2.0l = 3M Na + NO 3- : 8 moles/2.0l = 4M NO - 3
Clicker #4 When lead(ii) nitrate and potassium iodide are mixed, what precipitate will form? Pb(NO 3 ) 2(aq) + KI (aq) A) KNO 3 B) KI C) Pb(NO 3 ) 2 D) PbI 2 E) No precipitate will form. Solubility Rules 1. Most nitrate salts are soluble. 2. Most salts of sodium, potassium, and ammonium cations are soluble. 3. Most chloride and iodide salts are soluble. Exceptions: Ag + and Pb 2+. 4. Most sulfate salts are soluble. Exceptions: Ca 2+, Ba 2+, and Pb 2+. 5. Most hydroxide salts are only slightly soluble. Soluble ones are: Na +, K +, and Ca 2+. 6. Most sulfide, carbonate, and phosphate salts are only slightly soluble.
Example You are given 100.0mL of a 0.1M solution of Pb(NO 3 ) 2. You have a 0.1M solution of KI. a) What volume of KI solution do you need to completely react with Pb(NO 3 ) 2?
Example You are given 100.0mL of a 0.1M solution of Pb(NO 3 ) 2. You have a 0.1M solution of KI. a) What volume of KI solution do you need to completely react with Pb(NO 3 ) 2? b) What is the mass of solid produced?
Example You are given 100.0mL of a 0.1M solution of Pb(NO 3 ) 2. You have a 0.1M solution of KI. a) What volume of KI solution do you need to completely react with Pb(NO 3 ) 2? b) What is the mass of solid produced? c) What are the concentrations of the ions left in solution after the reaction is complete?
Clicker #5 What ions are left in solution after the reaction is complete? I. Pb 2+ II. NO 3 III. K + IV. I A) II and III B) I and IV C) II, III and IV D) I, II, III and IV E) No ions are left in solution after the reaction is complete.
Example Same reaction (and volumes) but different amounts: Pb(NO 3 ) 2(aq) + 2KI (aq) PbI 2(s) + 2KNO 3(aq) 0.0100 mol 0.0500 mol What is the mass of solid produced? What are the concentrations of the ions left in solution after the reaction is complete?
Clicker #6 What ions are left in solution after the reaction is complete? I. Pb 2+ II. NO 3 III. K + IV. I A) II and III B) I and IV C) II, III and IV D) I, II, III and IV E) No ions are left in solution after the reaction is complete.