Part C Questions 2011 Exam

Q 66-68 are based on the following Unbalanced Equation O2 (g) O3 (g) 66. Balance the equation using the smallest whole-number coefficients 67. Identify the type of Bonding between the atoms of oxygen Identify , in terms of electron configuration, why an oxygen molecule is more stable than an oxygen atom. electricity

(“electricity” written over the arrow) Q 66-68 are based on the following Unbalanced Equation O2 (g) O3 (g) (“electricity” written over the arrow) 66. Balance the equation using the smallest whole-number coefficients 3 O2 2 O3 (Balance for Mass; 6 O atoms on each side) 67. Identify the type of Bonding between the atoms of oxygen Ans: Oxygen has 6 valence electrons and is a nonmetal; bonding will be covalent Identify , in terms of electron configuration, why an oxygen molecule is more stable than an oxygen atom. Ans. A single O atom has six valence electrons and so does not have a stable octet

Q 69-70 are based on data for four components of natural gas Boiling Point at Standard Pressure ( oC ) Butane -0.5 Ethane -88.6 Methane -161.6 Propane -42.1 Q69. Identify a process used to separate the components of natural gas. Q70. List the four components of natural gas in order of increasing strength of intermolecular forces.

Q70. List in order of increasing strength of intermolecular forces. Components of Natural Gas Boiling Point at Standard Pressure ( oC ) Butane -0.5 Ethane -88.6 Methane -161.6 Propane -42.1 69. Ans: Distillation (You want a separation technique based on differences in boiling points/condensation points). Distillation or selective condensation are possible processes). Q70. List in order of increasing strength of intermolecular forces. ( recall: the weaker the forces of attraction between molecules, the lower the boiling pts) Answer: methane ethane propane butane Photos from POGIL on Distillation and Wikipedia

Typical lab Distillation Apparatus www.chemheritage.org

Q 71-73 are based on the following reaction NaCl + NH3 + CO2 + H2O Q 71-73 are based on the following reaction NaCl + NH3 + CO2 + H2O NaHCO3 + NH4Cl Write the chemical formula for one compound in the equation that contains both ionic bonds and covalent bonds. Explain, in terms of electronegativity difference, why the bond between hydrogen and oxygen in a water molecule is more polar than the bond between hydrogen and nitrogen in an ammonia molecule. In the space in your answer booklet, draw a Lewis dot diagram for the reactant containing nitrogen in the equation.

NaCl + NH3 + CO2 + H2O NaHCO3 + NH4Cl Either NaHCO3 or NH4Cl are acceptable answers Compounds that contain polyatomic ions (HCO3 - or NH4 +will have both ionic bonds and covalent bonds (Table E: Selected Polyatomic Ions) ANS: The electronegativity difference between oxygen and hydrogen (3.4-2.2 = 1.2) is greater than the electronegativity difference between nitrogen and hydrogen (3.0-2.2 = 0.8) and so the bond between oxygen and hydrogen in water is more polar than the bond between nitrogen and hydrogen in ammonia. (Use table S for Electronegativity values) 73. Ans: Draw a dot diagram for NH3 (N has 5 valence electrons and each H atom has 1 valence electron; atoms will bond in order to achieve the same electron configuration as a noble gas)

73. Ans: Draw a dot diagram for NH3 N has 5 valence electrons (2-5 is the electron configuration listed in P. Table) H atoms have 1 valence electron Atoms will bond to achieve the same electron configuration as a noble gas. Start by drawing the dot structures of each atom Make shared pairs where needed Tidy up dot diagram

Questions 74 – 76 are based on the following Data Table Mixture 1 Mixture 2 composition NaCl in H2O Fe filings in H2O Student observations Colorless liquid No visible solid in bottom of beaker Black solid on bottom of beaker Other data Mass of dissolved NaCl (s) = 2.9 g Mass of Fe (s) = 15.9 g Density of Fe(s) = 7.87 g/cm3 Classify each mixture using the term “homogeneous” or the term “heterogeneous”. Determine the volume of the Fe filings used to produce mixture 2. Describe a procedure to physically remove the water from mixture 1.

Mixture 1 is homogeneous, Mixture 2 is heterogeneous. composition NaCl in H2O Fe filings in H2O Student observations Colorless liquid No visible solid in bottom of beaker Black solid on bottom of beaker Other data Mass of dissolved NaCl (s) = 2.9 g Mass of Fe (s) = 15.9 g Density of Fe(s) = 7.87 g/cm3 Mixture 1 is homogeneous, Mixture 2 is heterogeneous. Density = 7.87 g/cm3 so 7.87 g in 1 cm3 15.9 g x ________ = ______ cm 3 (You are given mass and density and need to find the volume. Solve with dimensional analysis or use density formula in table T to solve for missing variable) Water can be removed by………….. 1 cm3 2.02 7.87 g

Other ways of removing water include” : Heating Salt Water removes the H2O from the Salt Water Mixture leaving NaCl behind. (Pictures from Wikipedia (http://upload.wikimedia.org/wikipedia/commons/4/43/Image-Zigong_Salt.jpg and http://upload.wikimedia.org/wikipedia/commons/9/9f/SaltCrystaUSGOV.jpg ) Other ways of removing water include” : Just allowing the water to evaporate at room temperature Removing water by distillation since Water and NaCl will have very different boiling points Salt Crystal NaCl (s)

Q 77-79 involve a lab experiment with Aluminum foil and Copper(II) chloride solution. The reaction equation is given and student observations are listed in a table. 2 Al (s) + 3 CuCl2 (aq) 3 Cu (s) + 2 AlCl3 (aq) Procedure Observation In a beaker, completely dissolve 5.0 g of CuCl2 in 80.0 mL of water. The solution is blue green Cut 1.5 g of Al (s) foil into small pieces. Add all the foil to the mixture in the beaker. Stir the contents for 1 min. The surface of the Al(s) foil appears partially black. The beaker feels warm to the touch. Observe the beaker and contents after 10 minutes The liquid in the beaker appears colorless A reddish-brown solid is seen at the bottom of the beaker Some pieces of Al(s) with a partially black coating remain in the beaker http://www.youtube.com/watch?v=zg-gsLEGk2A&feature=related for youtube video for this experiment

State one observation that indicates Cu+2 ions became Cu atoms. Procedure Observation In a beaker, completely dissolve 5.0 g of CuCl2 in 80.0 mL of water. The solution is blue green Cut 1.5 g of Al (s) foil into small pieces. Add all the foil to the mixture in the beaker. Stir the contents for 1 min. The surface of the Al(s) foil appears partially black. The beaker feels warm to the touch. Observe the beaker and contents after 10 minutes The liquid in the beaker appears colorless A reddish-brown solid is seen at the bottom of the beaker Some pieces of Al(s) with a partially black coating remain in the beaker State one observation that indicates Cu+2 ions became Cu atoms. Possible Answers: The solution is no longer blue or blue green (characteristic of Cu+2 ions in aqueous solution) . Or A reddish-brown solid is formed (corresponds to color of copper)

Q 77-79 continued 2 Al (s) + 3 CuCl2 (aq) 3 Cu (s) + 2 AlCl3 (aq) Describe one change in the procedure that would cause the reaction to occur at a faster rate. Possible Answers: Increase the concentrations of the CuCl2 solution Cut the aluminum into even smaller pieces Use a catalyst Use heated solutions State one safety procedure the student should perform after completing the laboratory activity. Possible answers: wash hands before leaving the lab or dispose of chemicals as teacher instructs or wash and return equipment to cabinets, etc.

Ans: beverage is acidic because its pH is less than than 7 Base your answers to questions 80 through 82 on the information below. Some carbonated beverages are made by forcing carbon dioxide gas into a beverage solution. When a bottle of one kind of carbonated beverage is first opened, the beverage has a pH value of 3. State, in terms of the pH scale, why this beverage is classified as acidic. Ans: beverage is acidic because its pH is less than than 7

What happens when CO2 (g) is bubbled through water ? (Hint; See table K Common Acids

81 Using Table M, identify one indicator that is yellow in a solution that has the same pH value as this beverage. Use Table L, Possible Answers = bromthymol blue, bromcresol green or thymol blue 82 After the beverage bottle is left open for several hours, the hydronium ion concentration in the beverage solution decreases to 1/1000 of the original concentration. Determine the new pH of the beverage solution. Started at pH = 3 ( so H + ion concentration = 10 –pH = 1 x 10-3 M (mol/L) New H+ concentration = 1 x 10-3 ÷ 1000 = 1 x 10-6 M Remember pH = -log (H+) so the new pH = 6

Base your answers to questions 83 through 85 on the information below. Polonium-210 occurs naturally, but is scarce. Polonium-210 is primarily used in devices designed to eliminate static electricity in machinery. It is also used in brushes to remove dust from camera lenses. Polonium-210 can be created in the laboratory by bombarding bismuth-209 with neutrons to create bismuth-210. The bismuth-210 undergoes beta decay to produce polonium-210. Polonium-210 has a half-life of 138 days and undergoes alpha decay. State one beneficial use of Po-210. (Extract answer from reading passage above)

Base your answers to questions 83 through 85 on the information below. Polonium-210 occurs naturally, but is scarce. Polonium-210 is primarily used in devices designed to eliminate static electricity in machinery. It is also used in brushes to remove dust from camera lenses. Polonium-210 can be created in the laboratory by bombarding bismuth-209 with neutrons to create bismuth-210. The bismuth-210 undergoes beta decay to produce polonium-210. Polonium-210 has a half-life of 138 days and undergoes alpha decay. Complete the nuclear equation in your answer booklet for the decay of Po-210, by writing a notation for the missing product. (Use ref table O, N and periodic table) Ans booklet: 210 Po 4He + ________ 2 84

Base your answers to questions 83 through 85 on the information below. Polonium-210 occurs naturally, but is scarce. Polonium-210 is primarily used in devices designed to eliminate static electricity in machinery. It is also used in brushes to remove dust from camera lenses. Polonium-210 can be created in the laboratory by bombarding bismuth-209 with neutrons to create bismuth-210. The bismuth-210 undergoes beta decay to produce polonium-210. Polonium-210 has a half-life of 138 days and undergoes alpha decay. Complete the nuclear equation in your answer booklet for the decay of Po-210, by writing a notation for the missing product. (Use ref table O, N and periodic table) Ans booklet: 210Po 4He + 206Pb 2 84 82

# of half-lives = total elapsed time ÷ half-life of isotope Determine the total mass of an original 28.0-milligram sample of Po-210 that remains unchanged after 414 days. Steps: (1) determine the number of half-lives during the elapsed time period # of half-lives = total elapsed time ÷ half-life of isotope 414 days ÷ 138 = 3 half-lives (2) Setup figure to predict the remaining mass 28.0 mg

# of half-lives = total elapsed time ÷ half-life of isotope Determine the total mass of an original 28.0-milligram sample of Po-210 that remains unchanged after 414 days. Steps: (1) determine the number of half-lives during the elapsed time period # of half-lives = total elapsed time ÷ half-life of isotope 414 days ÷ 138 = 3 half-lives (2) Setup figure to predict the remaining mass 28.0 mg 7.0 mg 14.0 mg 3.5 mg