Unit 1: Atomic Structure & Properties - Hw #3

The mass percent of carbon in pure glucose, C₆H₁₂O₆, is 40.0%. A chemist analyzes an impure sample of glucose and determines that the mass percent of carbon is 38.2%. Which of the following impurities could account for the low mass percent of carbon in the sample? A. Water, H₂O B. Ribose, C₅H₁₀O₅ C. Fructose, C₆H₁₂O₆, an isomer of glucose D. Sucrose, C₁₂H₂₂O₁₁

A. Water, H₂O

Cu(s) + 4 HNO₃(aq) → Cu(NO₃)₂(aq) + 2 NO₂(g) + 2 H₂O(I) Each student in a class placed a 2.00g sample of a mixture of Cu and Al in a beaker and placed the beaker in a fume hood. The students slowly poured 15.0 mL of 15.8 M HNO₃(aq) into their beakers. The reaction between the copper in the mixture and the HNO₃(aq) is represented by the equation above. The students observed that a brown gas was released from the beakers and that the solutions turned blue, indicating the formation of Cu²⁺(aq). The solutions were then diluted with distilled water to known volumes. The students determined the the reaction produced 0.010 mol of Cu(NO₃)₂. Based on the measurement, what was the percent of Cu by mass in the original 2.00g sample of the mixture? A. 16% B. 32% C. 64% D. 96%

B. 32%

A sample of a compound that contains only the elements C, H, and N is completely burned in O₂ to produce 44.0g of CO₂, 45.0g of H₂O, and some NO₂. A possible empirical formula of the compound is A. CH₂N B. CH₅N C. C₂H₅N D. C₃H₃N₂

B. CH₅N

The compound CCl₄ is nonflammable and was once commonly used in fire extinguishers. On the basis of the periodic properties, which of the following compounds can most likely be used as a fire-resistant chemical? A. BCl₃ B. CH₄ C. CBr₄ D. PbCl₂

C. CBr₄

What is the empirical formula of an oxide of chromium that is 48% oxygen by mass? A. CrO B. CrO₂ C. CrO₃ D. Cr₂O E. Cr₂O₃

C. CrO₃

Complete combustion of a sample of a hydrocarbon in excess oxygen produces equimolar quantities of carbon dioxide and water. Which of the following could be the molecular formula of the compound? A. C₂H₂ B. C₂H₆ C. C₄H₈ D. C₆H₆

C. C₄H₈

Consider atoms of the following elements. Assume that the atoms are in the ground state. The atom that contains only one electron in the highest occupied energy sublevel A. S B. Ca C. Ga D. Sb E. Br

C. Ga

To gravimetrically analyze the silver content of a piece of jewelry made from an alloy of Ag and Cu, a student dissolves a small pre weighted sample of HNO₃(aq). Ag⁺(aq) and Cu²⁺(aq) ions form in the solution. Which of the following should be the next step in the analytical process? A. Centrifuging the solution to isolate the heavier ions B. Evaporating the solution to recover the dissolver nitrates C. Adding enough base solution to bring the pH up to 7.0 D. Adding a solution containing an anion that forms an insoluble salt with only one of the metal ions

D. Adding a solution containing an anion that forms an insoluble salt with only one of the metal ions

Which of the following correctly identifies which has the higher first-ionization energy, Cl or Ar, and supplies the best justification? A. Cl, because of its higher electronegativity B. Cl, because of its higher electron affinity C. Ar, because of its completely filled valence shell D. Ar, because of its higher effective nuclear charge

D. Ar, because of its higher effective nuclear charge

To determine the percentage of water in a hydrated salt, a student heated a 1.2346 g sample of the salt for 30 minutes; when cooled to room temperature, the sample weighed 1.1857 g. After the sample was heated for an additional 10 minutes and again cooled to room temperature, the sample weighed 1.1632 g. Which of the following should the student do next? A. Use the smallest mass value to calculate the percentage of water in the hydrated salt. B. Repeat the experiment with a new sample of the same mass and average the results. C. Repeat the experiment with a new sample that has a different mass. D. Reheat the sample until its mass is constant. E. Use the average of the mass values obtained after the two heatings to calculate the percentage of water in the hydrated salt.

D. Reheat the sample until its mass is constant.

Which of the following correctly compares periodic properties of two elements and provides an accurate explanation for that difference? A. The first ionization energy of Al is greater than that of B because Al has a larger nuclear charge that B does. B. The first ionization energy of F is greater than that of O because O has a higher electronegativity than F has. C. The atomic radius of Ca is larger than that of Mg because the valence electrons in Mg experience more shielding than the valence electrons in Ca do. D. The atomic radius of Cl is smaller than that of S because Cl has a larger nuclear charge that S does.

D. The atomic radius of Cl is smaller than that of S because Cl has a larger nuclear charge that S does.

A sample of a solid labeled as NaCl may be impure. A student analyzes the sample and determines that it contains 75% chlorine by mass. Pure NaCl(s) contains 61% chlorine by mass. Which of the following statements is consistent with the data? A. The sample contains only NaCl(s). B. The sample contains NaCl(s) and NaI(s). C. The sample contains NaCl(s) and KCl(s). D. The sample contains NaCl(s) and LiCl(s).

D. The sample contains NaCl(s) and LiCl(s).

The percentage of silver in a solid sample is determined gravimetrically by converting the silver to Ag+(aq) and precipitating it as silver chloride. Failure to do which of the following could cause errors in the analysis? I. Account for the mass of the weighing paper when determining the mass of the sample II. Measure the temperature during the precipitation reaction III. Wash the precipitate IV. Heat the AgCl precipitate to constant mass A. I only B. I and II C. I and IV D. II and III E. I, III, and IV

E. I, III, and IV