3) What is the correct value for Avogadro's number? 3) A) x 1033 B) x 1023 C) x D) x 1022

Transcription

1 CHM1025 Exam 3 Chapters 6, 7, & 8 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) How many hydrogen atoms are in 35.0 grams of hydrogen gas? 1) A) 2.09 x 1025 B) 2.12 x 1025 C) 1.05 x 1025 D) 4.25 x ) Which of the following statements about empirical formulas is incorrect? 2) A) The molecular formula can be the same as the empirical formula in some situations. B) An empirical formula represents a molecule. C) An empirical formula gives the smallest whole number ratio of each type of atom in a molecule. D) An empirical formula must be multiplied by an integer to obtain the molecular formula. 3) What is the correct value for Avogadro's number? 3) A) x 1033 B) x 1023 C) x D) x ) Which of the following statements about redox reactions is FALSE? 4) A) Oxidation is the loss of electrons. B) A reaction involving elemental oxygen is a redox reaction. C) Reduction is the gain of electrons. D) A reaction can result in either oxidation or reduction, not both. 5) If you had an aqueous mixture that contained Ag+, K+, and Pb+2 cations, how many different solids could precipitate if a chloride solution was added? A) 2 B) 3 C) no solids will precipitate D) 1 5) 6) You have 10.0 g each of Na, C, Pb and Ne. Which contains the smallest number of moles? 6) A) C B) Pb C) Ne D) Na 7) What type of reaction is the generic equation? 7) A) double-displacement B) synthesis/combination C) single displacement D) decomposition

2 8) Methane gas (CH 4 ), on complete combustion in air, produces: 1. CO 2 2. H 2 3. H 2 O A) 1 and 2 only B) 2 and 3 only C) 1 and 3 only D) All of 1 and 2 only 8) 9) In comparing 1 mole of carbon atoms to one mole of magnesium atoms, which statement is true? 9) A) The mass of 1 mole of carbon is greater than the mass of 1 mole of magnesium. B) The mass of 1 mole of carbon is the same as the mass of 1 mole of magnesium. C) The mass of 1 mole of magnesium is greater than the mass of 1 mole of carbon. D) There are more atoms in 1 mole of magnesium than in 1 mole of carbon. 10) Which of the following statements about balancing reactions is FALSE? 10) A) Subscripts are multiplied by the coefficients to determine the number of atoms in a compound. B) Coefficients are added to compounds to ensure both sides of the reaction have equal numbers of each atom. C) When coefficients are added the type of compounds is changed in the chemical reaction. D) If there is no coefficient or subscript, a one is implied. 11) What are the coefficients for the following reaction when it is properly balanced? 11) nitrogen monoxide + carbon monoxide nitrogen + carbon dioxide A) 2, 2, 1, 2 B) 2, 1, 1, 2 C) 2, 2, 2, 1 D) 1, 1, 2, 2

3 Short Answer Problems. Show ALL calculations. 1. Ethanethiol (C2H6S) is a compound with a disagreeable odor that can be used to impart an odor to natural gas. a) Write a balanced equation to represent the combustion of ethanethiol. b) If 28.7 g of ethanethiol reacted, what mass of sulfur is contained in that sample?

4 2. Butanedione, a component of butter and body odor, has a cheesy smell. Elemental analysis of butanedione gave the mass percent composition: C, 55.80%; H, 7.03% and the rest is O. The molar mass of butanedione is g/mol. Determine the molecular formula of butanedione.

5 3. A solution contains one or more of the following ions: Ag +, Ca 2+ and Cu 2+. When sodium chloride is added to the solution, no precipitate occurs. When sodium sulfate is added to the solution, white precipitate occurs. The precipitate is filtered off and the sodium carbonate is added to the remaining solution, producing a precipitate. a) Which ions were present in the original solution (provide explanations for your answers). b) Write net ionic equations for the formation of each of the precipitates observed. END OF QUESTIONS

6 CHM1025 Exam 3 Chapters 6, 7, & 8 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) How many atoms are in 1.50 moles of fluorine gas? 1) A) 1.81 x 1024 B) C) 9.03 x 1023 D) x ) Which of the following compounds is INSOLUBLE? 2) A) potassium acetate B) aluminum sulfide C) magnesium bromide D) lithium carbonate 3) What are the coefficients for the following reaction when it is properly balanced? 3) Na 3 PO 4 + Ba(NO 3 ) 2 NaNO 3 + Ba 3 (PO 4 ) 2 A) 2, 3, 1, 6 B) 6, 1, 3, 2 C) 2, 1, 1, 3 D) 2, 3, 6, 1 4) What is the molar mass of aluminum sulfate? 4) A) g/mol B) g/mol C) g/mol D) g/mol E) g/mol 5) Considering the following precipitation reaction: 5) Pb(NO 3 ) 2 (aq) + 2KI(aq) PbI 2 (s) + 2KNO 3 (aq) Which ion(s) would not be present in the net ionic equation? A) Pb 2+, NO - 3 B) K +, I- C) K +, Pb 2+ D) K +, NO 3 - E) All the above ions are in the net ionic equation. 1

7 6) Vitamin C is known chemically by the name ascorbic acid. Determine the empirical formula of ascorbic acid if it is composed of 40.92% carbon, 4.58% hydrogen, and 54.50% oxygen. A) C3H4O3 B) CHO C) C2H3O2 D) CH2O 6) 7) The empirical formula of a compound: 7) A) indicates the structure of the molecule. B) is the same as the molecular formula. C) indicates the simplest ratio of atoms in the compound. D) describes the mass relationships in a molecule. E) is none of the above 8) In writing the chemical equation for a precipitation reaction, what abbreviation of the physical state must appear with one of the products? A) (s) B) (l) C) (w) D) (g) 8) 9) What would the empirical formula be for the molecular compound C 6 H 9 O 4? 9) A) CH 3 O 2 B) C 3 H 6 O2 C) C 3 H 9 O 4 D) C 2 H 3 O 2 10) A reaction which forms a solid product is an example of a(n). 10) A) combustion reaction B) oxidation-reduction reaction C) gas evolution reaction D) precipitation reaction 11) What is the gas produced when hydrochloric acid is reacted with ammonium carbonate? 11) A) ammonia B) carbon dioxide C) chlorine D) hydrogen 12) One mole of ammonium nitrate contains: 12) A) 2 moles of oxygen. B) 3 moles of hydrogen. C) 1 mole of nitrogen. D) 2 moles of nitrogen. 2

8 13) How many moles of fluorine are in 3.2 moles of xenon hexafluoride? 13) A) 22.4 B) 19.2 C) 12.8 D) 16 14) Bauxite is an ore that contains the element aluminum. If you obtained 108 grams of aluminum from an ore sample that initially weighed 204 grams, what is the mass percent of aluminum in this bauxite ore? A) 0.53 B) 47.1 C) 15.6 D) ) 15) What is the mass of 3.09 x 1024 atoms of sulfur in grams? 15) A) 165 B) 9.64 x 1022 C) 9.91 x 1025 D) ) A precipitate is expected to be formed when an aqueous solution of sodium sulfate is added to an aqueous solution of A) barium chloride B) potassium chloride C) magnesium chloride D) iron(iii) chloride 16) 17) In comparing 1 mole of carbon atoms to one mole of magnesium atoms, which statement is true? 17) A) The mass of 1 mole of carbon is the same as the mass of 1 mole of magnesium. B) The mass of 1 mole of carbon is greater than the mass of 1 mole of magnesium. C) There are more atoms in 1 mole of magnesium than in 1 mole of carbon. D) The mass of 1 mole of magnesium is greater than the mass of 1 mole of carbon. 18) What is the net ionic equation for the reaction of hydrochloric acid with potassium hydroxide? 18) A) HCl + KOH H 2 O + KCl B) H+ + OH- H 2 O C) 2H + +2Cl- + K OH- H 2 O + K Cl- D) H + + Cl - + K + + OH- H 2 O + K + + Cl - 3

9 19) What type of reaction is the generic equation A + BC AC + B? 19) A) single displacement B) double-displacement C) decomposition D) synthesis/combination 20) Methane gas (CH 4 ), on complete combustion in air, produces: 1. CO 2 2. H 2 3. H 2 O A) 1 and 3 only B) 1 and 2 only C) 2 and 3 only D) All of 1 and 2 only E) None of 20) 4