Stoichiometry Conversion factors 1 mole = 6.02 x 10 23 atoms (element) 1 mole = 6.02 x 10 23 molecules (covalent compounds) 1 mole = 6.02 x 10 23 formula units (ionic compounds) 1 mole (any gas @ STP) = 22.4 L Moles A = moles B (if balanced equation showing mole ratios) Isotopes Atoms of element with same atomic number (#p + ) and different mass number (p + + n 0 ) Weighted average mass= average is based on abundance of each isotope for an element Percent composition Part / whole x 100 = % Empirical formula (simplest wholenumber ratio of moles) % to mass mass to moles by least x til whole Stoichiometry calculations Use mole ratios and conversion factors to change from unit to unit Limiting reactant Reactant used up first Use mole ratios to determine Percent yield actual x 100 = % theoretical Solution stoichiometry Liters x mol/liter = moles (V x M = moles) Molarity of solution = molarity of each ion in solution x number of ions in formula
Solutions Solute + solvent Concentration of solution Molarity = moles solute / liter of solution Mass percent = mass solute / mass of solution x 100 Mole fraction = mole solute / total moles solution (usually with gases) Solution Stoichiometry Molarity of solution = molarity of each ion x number of ions in formula ex. 0.5 M K 2CrO 4 K 2CrO 4 2 K + + CrO 4 2 0.5 x 2 = 1.0 M K + and 0.5 M CrO 4 2 Energy of solutions Expand solute and solvent Mix solute and solvent endothermic exothermic Factors affecting solubility Structure: polarity Pressure: higher pressure means more gas dissolved Temperature: temperature, solid solubility temperature, gas solubility Solubility curves on line saturated under line unsaturated over line, supersaturated Equilibrium link: saturated solution @ equilibrium unsaturated solution K < 1 supersaturated solution K > 1 Electrolyte contains ions and will conduct Nonelectrolyte does not have mobile ions Rate of solution: Stir or agitate Smaller particle sizes Temperature Dilutions M 1 x V 1 = M 2 x V 2 Precipitation reactions Know your solubility rules!
Multiple Choice 1. What volume of 10.0 M NaOH solution must be used to prepare 500. ml of a 2.50 M solution? A) 125 ml B) 200 ml C) 250 ml D) 12.5 ml 2. Analysis of a sample of an oxide of chromium is reported as 26 g of chromium and 12 g of oxygen. From these data determine the empirical formula of this compound. A) CrO B) CrO3 C) Cr2O3 D) Cr4O6 3. How many moles of barium sulfide, BaS, will form when 60.0 ml of 1.0 M Ba(NO3)2 are mixed with 25.0 ml of 0.80 M K2S solution to form barium sulfide solid? A) 0.020 mol B) 0.040 mol C) 0.060 mol D) 0.10 mol 4. When 16 g of methane (CH4) and 32 g of oxygen (O2) reacted to produce carbon dioxide and water, 11 g of carbon dioxide was produced. Calculate the percent yield of carbon dioxide in this reaction. A) 5.0% B) 10% C) 25% D) 50% 5. A 50.0 ml solution of Fe 2+ is titrated with 0.0020 M KMnO4 to produce Fe 3+ and Mn 2+. Find the initial concentration of Fe 2+ if 20.0 ml of KMnO4 is required to reach the equivalence point. A) 0.000400 M Fe 2+ B) 0.000286 M Fe 2+ C) 0.00400 M Fe 2+ D) 0.00286 M Fe 2+ 6. Excess 0.1 M NaCl (aq) is added to 100 ml of 0.1 M AgNO 3 (aq). A white precipitate forms. Which is a correct description of the quantities present? liquid phase solid phase A) [Ag + ] = [Cl ] mol Ag + = mol Cl B) [Ag + ] < [Cl ] mol Ag + = mol Cl C) [Ag + ] = [Cl ] mol Ag + < mol Cl D) [Ag + ] > [Cl ] mol Ag + < mol Cl 7. What is the sodium ion concentration when 70.0 ml of 3.0 M Na 2CO 3 is added to 30.0 ml of 1.0 M NaHCO 3? A) 0.45 M B) 4.5 M C) 2.4 M D) 5.1 M 8. Which of the following solutions contains the largest number of ions? A) 500. ml of 0.100 M FeCl 3 B) 400. ml of 0.100 M Al(NO 3) 3 C) 600 ml of 0.200 M AlCl 3 D) 700. ml of 0.20 M NaOH
9. If a solution of sodium hydrogen carbonate is mixed with a solution containing an equal number of moles of nitric acid, then sodium nitrate, water and carbon dioxide are produced. What is the net ionic equation representing this reaction? A) NaHCO 3 (aq) + HNO 3 (aq) NaNO 3 (aq) + H 2O (l) + CO 2 (g) B) HCO 3 (aq) + HNO 3 (aq) NO 3 (aq) + H 2O (l) + CO 2(g) C) Na + (aq) + HCO 3 (aq) + HNO 3 (aq) Na + (aq) + NO 3 (aq) + H 2O (l) + CO 2(g) D) HCO 3 (aq) + H + (aq) H 2O (l) + CO 2(g) 10. Order the following solvents from least polar to most polar: C 6H 14 H 2O CH 3OH CHCl 3 A) H 2O < CH 3OH < CHCl 3 < C 6H 14 B) C 6H 14 < CH 3OH < CHCl 3 < H 2O C) CHCl 3 < C 6H 14 < CH 3OH < H 2O D) C 6H 14 < CHCl 3 < CH 3OH < H 2O 11. In column chromatography, the first substance eluted A) Has a high affinity for the mobile phase B) Is insoluble in the mobile phase C) Precipitates out of the mobile phase D) Moves more slowly through the stationary phase than other substances in solutions Free Response 1. The reaction between silver ion and solid zinc is represented by the following equation. 2Ag + + Zn Zn 2+ + 2Ag a) A 1.50 g sample of Zn is combined with 250. ml of 0.110 M AgNO 3 at 25 C. i) A student identifies the limiting reactant as zinc. Do you agree or disagree with this statement? Justify your answer. ii) On the basis of the limiting reactant that you identified in part (i), determine the value of [Zn 2+ ] after the reaction is complete. Assume that volume change is negligible. 2. An aqueous solution of antifreeze is 40.0% ethylene glycol (C 2H 6O 2) by mass. The density of the solution is 1.05 g/cm 3. a) Determine the mole fraction of the ethylene glycol solution b) Calculate the molarity of the solution
3. Answer the following questions about BeC 2O 4 and its hydrate. a) Calculate the mass percent of carbon in the hydrated form of the solid that has the formula BeC 2O 4 3H 2O b) If 3.21 g of BeC 2O 4 3H 2O is heated to 220. C, calculate the mass of BeC 2O 4 formed if the substance dehydrates completely BeC 2O 4 3H 2O BeC 2O 4 + 3H 2O c) A 0.345 g sample of anhydrous BeC 2O 4, which contains an inert impurity, was dissolved in sufficient water to produce 100. ml of solution. A 20.0 ml portion of the solution was titrated with KMnO 4 (aq). The balanced equation for the reaction that occurred is as follows: 16H + + 2MnO 4 + 5C 2O 4 2 2Mn 2+ + 10CO 2 + 8H 2O The volume of 0.0150 M KMnO 4 required to reach the equivalence point was 17.80 ml. i. For the titration at the equivalence point, calculate the number of moles of each of the following that reacted. MnO 4 C 2O 4 2
4. Answer the questions below that relate to the five aqueous solutions at 25 C below. solution 1 solution 2 solution 3 solution 4 solution 5 0.10 M 0.10 M 0.10 M 0.10 M 0.10 M Pb(NO 3) 2 NH 4Cl KMnO4 C 2H 5OH KC 2H 3O 2 a) Which solution has the highest boiling point? Explain. b) Identify a pair of the solutions that would produce of precipitate when mixed together. Write the formula of the precipitate. c) Which solution would be the least effective conductor of electricity? Explain. d) Identify the solution that can be identified by appearance alone. Describe the observation that supports your identification. e) Which solution would dissolve with an (+) ΔH? Explain.