1. Cobalt(II) chloride and lead(ii) acetate a. b. c. 2. Lithium hydrogen carbonate and hypochlorous acid a. b. c.

Transcription

1 Chemistry 101 SI 3 (Chapter 4, 5 & 6) Supplemental Instruction Chapter 4. I. For the following pairs of reagents, write (a) the balanced molecular equation, (b) the ionic equation, and (c) the net ionic equation. Be sure to include ALL STATES. If no reaction occurs, substitute NR for the NET IONIC EQUATION. 1. Cobalt(II) chloride and lead(ii) acetate 2. Lithium hydrogen carbonate and hypochlorous acid 4. Ammonium sulfide and nitric acid II. Oxidation-Reduction Reactions: Assign oxidation numbers to all atoms in the following equations. List the OXIDIZING AGENT and the REDUCING AGENT. 1. NO2 (aq) + Cr2O7 2- (aq) Cr 3+ (aq) + NO3 (aq) 2. S(s) + HNO 3 (aq) H2SO3(aq) + N2O(g) 3. Cr2O7 2- (aq) + CH3OH (aq) HCOOH (aq) + Cr 3+ (aq) 4. MnO4 (aq) + Cl (aq) Mn 2+ (aq) + Cl2(aq) III. Molarity and Dilution 1. Find the concentration of each ion present in the solution formed by adding together the following: ml of M K2SO4 and ml of M HNO3; ml of M Cu(NO3)2 and ml of M Fe(NH4)2(SO4)2. Assume all volumes are additive. 2. What mass in grams of NaCl would be required to bring 4.60 L of M NaCl solution to a molarity of , without changing the volume of the solution?

2 3. Find the following: How many grams of solute are present in 50.0 ml of M K2Cr2O7? If 4.00 g of (NH4)2SO4 are dissolved in enough water to make ml of solution, what is the molarity of that solution? How many ml of M CuSO4 contain 1.75 g of solute? IV. Solution Stoichiometry 1. A g sample of limestone rock is crushed to powder and then treated with ml of M HCl. The excess acid required ml of M NaOH for neutralization. Calculate the percent by mass of the calcium carbonate in the rock. 2. For the addition of ml of M calcium bromide to ml of M sodium oxalate, determine the following: Write the balanced molecular equation for the reaction. What is the limiting reagent? What is the molarity of all ions in the final solution? d. Assuming the reaction proceeds at 100 %, what volume of the limiting reagent is required to produce g of the precipitate if the concentrations remain the same? e. What molarity of the limiting reagent would be required if ml of that solution were used, and the desired amount of precipitate was g? Chapter 5. I. First Law Problems 1. A system gains 35 J of heat, but it also does 65 J of work. Calculate E. 2. A system evolves 50 J of heat and 75 J of work is done on the system. What is the internal energy change of the system? 3. When one mole of ice, H 2 O (s), is converted to H 2 O (l) at 0 C and 1 atm, 6.01 kj of heat is absorbed by the system. The molar volume, V/n, for ice and water is L, and L respectively. Calculate E and H. [1 L atm=101.3 J] 4. Calculate the total change in work, w, and internal energy, E, for each of the following processes. For your answers enumerate the results for q, w, and E for each step. (a) (b) 5.00 L of air expands to 20.0 L by heating it from 300 K to 1200 K at a constant pressure of 3.00 atm. The heat required for this process is 17.8 kj L of air initially at 3.00 atm is heated from 300 K to 1200 K while its volume is held constant. The heat required for this process is 12.8 kj. Page 2

3 (c) The hot gas from part (b) is allowed to expand isothermally (constant temp.) until its pressure drops to 3.00 atm and its volume reaches 20.0 L. The heat required in this step is 9.7 kj. [Hint: Energy is a state function! Find a relationship among the pathways a,b, and c! ] II. Heat Capacity and Calorimetry 5. In a styrofoam (coffee) - cup calorimeter, ml of 1.01 M NaOH and ml of 1.0 M HCl are mixed. Both solutions were originally at 23.8 C. After the reaction, the final temperature is 30.5 C. Assuming that all the solutions have a density of 1.0 g/cm 3 and a specific heat capacity of 4.18 J/g C, calculate the enthalpy change for the neutralization of HCl by NaOH. [Assume that no heat is lost to the surroundings or to the calorimeter. 6. A lead bullet with a mass of 8.00 g and traveling at 5.00 x 10 4 cm/s is imbedded in a wooden block weighing kg. If both the block and the bullet were initially at 25.0 C, what is the final temperature of the block containing the bullet? The specific heat of wood is 0.50 cal/g C; that of lead is cal/g C. 1 cal = J, and J = kg m 2 /s 2. { Assume no heat loss to the surroundings. You may also assume that the heat absorbed by the bullet is negligible! Why?} III. Enthalpy and Internal Energy 7. The complete combustion of benzene, C 6 H 6(l), at 25.0 C and 1 atm, produces 3269 kj of heat per mole. Assume that the product water condenses to the liquid state. Calculate H and E for the reaction. [Consider the condition to determine which state function is given, H or E?] 8. When SO 3 (g) decomposes to SO 2 (g) and O 2 (g) at 25.0 C and 1 atm 25.0 kj of heat is evolved per mole of reactant at constant volume. Calculate E and H for the reaction. Is this reaction more or less exothermic under constant pressure conditions? Why? 9. One mole of graphite, C(gr), is converted to CO(g) in the presence of oxygen at 25.0 C and 1 atm. In this process 26,416 cal or x 10 5 J of heat is evolved. (a) What is H f of CO(g)? (b) What is E, if the molar volume of graphite is L? IV. Hess s Law problems 1. Find Hrxn for the reaction below, from the following data: 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) H =??? N2(g) + O2(g) 2NO(g) H= 180.5kJ N2(g) + 3H2(g) 2NH3(g) H= 91.8kJ H2(g) + ½ O2(g) H2O(g) H= 241.8kJ 2. Find Hrxn for the reaction below, from the following data: 3H2(g) + 2C(s) + ½ O2 (g) C2H5OH(l) H =??? C2H5OH(l) + 3O2(g) 2CO2 (g) + 3H2O(l) H= 875kJ C(s) + O2(g) CO2(g) H= kJ H2(g) + ½ O2 (g) H2O(l) H= 285.8kJ Page 3

4 3. Find ΔH rxn for the reaction below, from the following data: CH4(g) + NH3(g) HCN(g) + 3H2(g) N2(g) + 3H2(g) 2NH3(g) C(s) + 2H2(g) CH4(g) H2(g) + 2C(s) + N2(g) 2HCN(g) H=??? H= 91.8kJ H= 74.9kJ H=+270.3kJ V. Heat of Formation Problems Use the standard enthalpies of formation in the table below to determine the change in enthalpy for the reactions which follow the table. Compound H f (kj/mol) Compound H f (kj/mol) CH4(g) 74.8 NaHCO3(s) CO2(g) NaOH(s) CO(g) NH3(g) 46.2 HCl(g) 92.3 NH4Cl(s) H2O(g) NO(g) H2O(l) NO2(g) H2S(g) 20.1 SO2(g) H2SO4(l) SO3(g) MgSO4(s) SnCl4(l) MnO(s) SnO(s) MnO2(s) SnO2(s) NaCl(s) ZnO(s) NaF(s) ZnS(s) NaOH(s) + HCl(g) NaCl(s) + H2O(g) H =??? 2. 2CO(g) + O2 (g) 2CO2(g) H =??? 3. CH4(g) + 2O2(g) CO2(g) + 2H2O(l) H =??? 4. 2H2S(g) + 3O2(g) 2H2O(l) + 2SO2 (g) H =??? 5. 2NO(g) + O2 (g) 2NO2 (g) H =??? Chapter A radio wave has a frequency of 20.0 MHz. (a) What is the speed of this electromagnetic radiation in a vacuum? (b) What is the wavelength of this light? (c) What is the energy of one photon of this light? (d) What is the energy of one mole of photons of this light? 2. A high powered laser is pulsed for ns. During this time, it emits a total of J of energy at a wavelength of 351 nm. How many photons does it emit during this time? 3. Is energy emitted or absorbed by each of the following electron transitions in a hydrogen atom? (a) The electron goes from n=3 to n=6. (b) The electron goes from its ground state to its ionized state. (c) The electron moves from nm to nm from the nucleus. Page 4

5 4. Photogrey lenses in glasses incorporate small amounts of silver chloride in the lens. When the light hits the AgCl particles, the following reaction occurs: AgCl Ag + Cl The silver metal that is formed causes the lenses to darken. The enthalpy change for this reaction is 3.10 x 10 3 kj/mol. Assuming that all of this energy must be supplied by light, what is the maximum wavelength of light that causes this reaction? 5. (a) What is the frequency of light emitted by an atom when an electron transition is made between states with energy 2.18 x J and 8.72 x J? (b) What energy levels in the hydrogen atom do these energy states correspond to? 6. It requires 222 kj/mol to eject electrons from potassium metal. (a) What is the minimum frequency of light necessary to emit electrons from potassium via the photoelectric effect? (b) What is the wavelength of this light? (c) If potassium is irradiated with light of 350 nm, what is the maximum possible kinetic energy of the emitted electrons? 7. How many orbitals are represented in an atom by the following designations? (a) p x (b) 4d (c) 2s (d) 5f (e) 2d 8. Which of the following are allowed sets of quantum numbers in an atom? (a) n=3, l=1, m l = -1; (b) n=3, l=1, m l = 2; (c) n=2, l=2, m l = 0 (d) n=9, l=0, m l = 0; (e) n=4, l= -2, m l = 1 For those combinations that are allowed, write the appropriate designation for the subshell to which the orbital belongs, such as 1s, etc 9. How many electrons in Antimony, Sb, have the quantum number (a) l = 2, (b) m l = 0, (c) n = Although no currently known elements contain electrons in the g orbitals in the ground state, it is possible that these elements will be found or that electrons in excited states of known elements could populate the g orbitals. For g orbitals, the value for l = 4. (a) What is the lowest possible value for n, for which g orbitals could exists? (b) What are the possible values for m l? (c) How many electrons could a set of g orbitals hold? Page 5