AVOGADRO EXAM Answers

Transcription

1 VGR XM nswers 1 Iodine-131 is a radioactive isotope used to treat hyperthyroidism (an overactive thyroid gland) and thyroid cancer. ow many protons, neutrons and electrons are there in a single atom of iodine-131? 5 student prepared the following graph to illustrate one aspect of ideal gas behaviour. owever, he forgot to label the axes. 131 protons, 131 neutrons, 131 electrons * 53 protons, 78 neutrons, 53 electrons 78 protons, 53 neutrons, 78 electrons 53 protons, 131 neutrons, 53 electrons 78 protons, 131 neutrons, 78 electrons 2 ata are given below for the hypothetical element avogadrium, symbol v. What is the average atomic weight of avogadrium? u u u * u Relative Fractional Isotope weight abundance v u 36.02% v u 63.98% Which of the following graphs could it be? Note: In the responses below, the symbols have their usual meanings: P is pressure; V is volume; T is kelvin temperature; n is amount in moles. P versus T, with n and V held constant T versus n, with P and V held constant PV versus T, with n held constant P versus V, with n and T held constant * PV/T versus P, with n held constant 6 Which substance, in the solid state, is likely to have the following characteristics: hard; brittle; soluble in water; high melting point? u l 2 * Rbl 3 Which of the following equations is not correct? (diamond) * 2 (g) 2 (g) + energy Na(g) + e Na (g) + energy Mg(g) + energy Mg 2+ (g) + 2e u(s) + energy u(l) Na + (g) + l (g) Nal(s) + energy 4 ow many electron pairs are there around the S atom in the SF 3 ion? three bonding pairs three bonding pairs and one unshared pair * three bonding pairs and two unshared pairs four bonding pairs and two unshared pairs u Ir 7 The mass of a sample is measured as g. ow many significant figures are there in this quantity? two three * four five six six bonding pairs 2 / VGR XM 2011 UNIVRSITY F WTRL

2 8 Graphite is best described as a hard, white solid a soft, white solid * a soft, black solid a hard, silvery solid a yellowish liquid 9 ccording to the World ealth rganization, the development of methods for the disinfection of drinking water is considered one of the major achievements of modern times. Which of the following substances has been widely used to disinfect drinking water? NaF 12 ow many grams of 2 6 can be made starting with 5.00 g Lil 4 and excess F 3, according to the following reaction? 3 Lil F 3 3 LiF + 3 lf g * 2.43 g 3.65 g 5.47 g 7.29 g 13 n isotope of a particular element has a mass number of 208 and it has 46 more neutrons than protons. What is the element? mercury, g 2 * l 2 polonium, Po lead, Pb 2 l bismuth, i * thallium, Tl 10 y the addition of water, 40.0 ml of 8.0 mol/l I is diluted to ml. What is the molar concentration of I after dilution? 0.50 mol/l 1.0 mol/l 1.6 mol/l 14 The covalent radius of hydrogen is 74 pm. ssume that hydrogen atoms could be arranged side-by-side in a single line, as suggested in the diagram below. What is the mass of a line of hydrogen atoms that is exactly 10 cm long? g * g 10 cm * 2.0 mol/l g 4.0 mol/l g 11 Which of the following substances does not produce ions when it is added to water? sodium metal, Na * ethanol, 3 2 citric acid, carbon dioxide, 2 potassium nitrate, KN g 15 What is the -- angle in the ethene molecule, 2 4? hoose the closest value. 45 o 90 o 109 o * 120 o 180 o 2011 UNIVRSITY F WTRL VGR XM / 3

3 16 process for producing iron, Fe, is based on the following reactions. 2 (g) + 2 (g) 2 (g) Fe 2 3 (s) + 3 (g) 2 Fe(s) (g) What mass of 2 is required to produce kg Fe? 19 kg 20 Which of the following Lewis structures is incorrect? l * 43 kg 50 kg * F P F 75 kg F 170 kg 17 To which one of these pairs of elements does the term metalloids apply most fittingly apply? potassium and strontium nickel and silver lithium and beryllium sulfur and bromine * boron and silicon 18 Which of the following statements is true? Silicon conducts electricity better than aluminum. Sulfur is more electronegative than chlorine. N * The +1 oxidation state is common for sodium but not for aluminum. The ionic radius of l is greater than that of S 2. The atomic radius of aluminum is greater than that of sodium. 19 Which of the following molecules has the longest bond? * I 2 Ir 21 The following equation represents a fission reaction in which an isotope of uranium is bombarded with neutrons. What must be the value of x in order to balance the equation? 1 n U 141 a + 92 Kr + x 1 n Il * 3 l 2 4 r 2 4 / VGR XM 2011 UNIVRSITY F WTRL

4 22 The concentration of + in stomach acid is about a million times greater than it is in pure water. What is the approximate p of stomach acid at 25 o? * The first six ionization energies of a particular element are shown in the graph below. To which group of the periodic table does this element belong? nergy I(5) I(6) L gas cylinder contains neon gas with a measured pressure of 65.0 kpa at 315 K. The 10.0 L cylinder is then connected to an empty cylinder of unknown volume, and the neon gas expands to fill both cylinders. If the final pressure is found to be 46.3 kpa at 315 K, then what is the volume of the second cylinder? * 4.04 L 13.0 L 14.0 L 1.87 L 7.12 L 26 Which of the following atoms, in their ground electronic states, does not have a half-filled subshell? * Ga Mn I(1) I(2) I(3) I(4) K s number of electrons removed 27 What is the formula of the stable compound that contains only magnesium and phosphate ions? group1 group 2 group 13 * group 14 group 15 Mg 2 (P 4 ) 3 MgP 4 Mg(P 4 ) 3 Mg 3 P 4 * Mg 3 (P 4 ) 2 24 Which of the following produces the greatest mass of metal upon reduction with one mole of electrons? l 3+ u 2+ Pt 2+ Mg 2+ * g + 28 Suppose 10.0 ml of a 1.0 mol/l solution of l is diluted with water to a final volume of 1.0 L. What happened to the p of the solution? The p decreases by 10 units. The p increases by 10 units. The p decreases by 2 units. * The p increases by 2 units. The p changes by less than 1 unit UNIVRSITY F WTRL VGR XM / 5

5 29 ow many moles of r are in ml of a solution that is mol/l with respect to Nar and mol/l with respect to ar 2? 33 sulfuric acid ( 2 S 4 ) solution has a density of 1.29 g/ml and it is 38% by mass 2 S 4. What is the molar concentration of this solution? mol mol * mol mol mol 0.38 mol/l 0.49 mol/l 0.98 mol/l * 5.0 mol/l 10.0 mol/l Molar masses, in g/mol, 1.008, S, Select the one correct or the one incorrect statement. * Ionization energies generally decrease from left to right across a row in the periodic table. Ionization energies generally decrease from top to bottom in a vertical group of the periodic table. tomic sizes generally increase from top to bottom in a vertical group of the periodic table. The atomic radius generally decreases from left to right across a row in the periodic table. The second ionization energy of an element is always larger than the first ionization energy. 31 eviations from ideal gas behaviour are most evident for a gas at 34 In the structure below, X represents an unidentified element. 2 X What is the possible identity of X? carbon, nitrogen, N * sulfur, S phosphorus, P high temperature and high pressure chlorine, l low temperature and low pressure high temperature and low pressure * low temperature and high pressure high temperature in a large volume 32 The partial pressures of three gases in a 5.00 L cylinder at 1000 o are as follows. 2 : 239 kpa 2 : 72 kpa 2 : 106 kpa ow many moles of 2 are in the cylinder? 35 particular airship (a zeppelin or blimp) uses 8 16 as fuel To counterbalance the weight loss of fuel used in the operation of the airship, part of the water contained in the exhaust gases must be condensed and retained. The remainder of the water and the 2 are vented to the atmosphere. If the mass of water retained exactly offsets the mass of fuel burned, what percentage of the water is retained? mol 22% mol * mol mol mol 39% 11% 61% * 78% 6 / VGR XM 2011 UNIVRSITY F WTRL

6 36 In the following structures for four different carbonhydrogen compounds, a carbon atom exists wherever a line ends or meets another line, and the number of atoms needed to complete each carbon atom s four bonds are assumed to be present. 39 To a weighed, clean and dry L volumetric flask is added some pure N 4 l. The flask is reweighed. Then distilled water is added to dissolve the N 4 l, and finally enough water is added, with stirring, to bring the solution to the L mark. The flask is reweighed. ata are shown below. (1) (2) (3) (4) Mass of clean and dry L flask: Mass of flask plus N 4 l: Mass of flask plus N 4 l plus water: g g g Which two compounds are isomers with the formula 6 10? Which of the following statements concerning the resulting solution is correct? (1) and (2) (2) and (3) * (3) and (4) (2) and (4) The molar concentration of N 4 l is 5.23 mol/l. The density of the solution is 1.24 g/ml. The solution is 22.6% N 4 l by mass. ll of, and are true. (1) and (3) * None of, and are true. 37 Refer to the information and structures given in question 36. In which compound are all the carboncarbon bond lengths the same? * (1) (2) (3) (4) none of the above 38 In a well-insulated container, an endothermic chemical reaction takes place. When the reaction is done, the temperature of the contents will be 40 ne of two identical balloons contained carbon dioxide ( 2, 44 g mol 1 ) and the other contained hydrogen ( 2, 2.0 g mol 1 ). If it took 24 hours for all of the 2 to escape from its balloon, how long did it take for all of the 2 to escape? (hoose the closest value.) int: For a sample of gas at a fixed temperature T, the average speed of molecules is inversely proportional to m 1/2, where m is the molecular mass. 530 hours * 110 hours 230 hours 1 hour higher than before the reaction began 5 hours higher or lower than at the start of the reaction, depending on the heat capacities of the substances involved the same as before the reaction began * lower than before the reaction began independent of the heat capacities of the substances involved 2011 UNIVRSITY F WTRL VGR XM / 7