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Chemical Compound Questions and Answers

Get answers to questions about chemical compounds, including formulas, names, and balancing equations.

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Chemical Compound Questions and Answers

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  1. Question • An element’s most stable ion forms an ionic compound with chlorine having the formula XCl2. If the ion has 36 electrons, what is the element from which the ion comes? a) Kr b) Se c) Sr d) Rb e) None of the above

  2. Answer • c) Sr • The ion has a 2+ charge since it is combined with two 1– charged ions of a Group VIIA element. Thus, the element must have 38 electrons.

  3. Question • ______ form ions with a 2+ charge when they react with nonmetals. a) Group IA elements b) Group IIA elements c) Group VIIA elements d) Group VIIIA elements e) None of the above

  4. Answer • b) Group IIA elements • Group IIA elements form ions with 2+ charge and combine with nonmetals in binary compounds.

  5. Question • Which is not the correct chemical formula for the compound named? a) Potassium phosphate, K3PO4 b) Iron(II) oxide, FeO c) Calcium carbonate, CaCO3 d) Sodium sulfide, NaS e) Lithium nitrate, LiNO3

  6. Answer • d) Sodium sulfide, NaS • Sodium sulfide is a binary compound composed of a Group IA element whose charge in compounds is +1 and a Group VIA element whose charge in binary compounds is commonly –2. This means that two sodium ions must be combined with one sulfide ion for a neutral compound.

  7. Question • Which of the following is not the correct chemical formula for the compound named? • Li2O, lithium oxide • FePO4, iron(III) phosphate • HF, hydrogen fluoride • BaCl2, barium dichloride • Mg3N2, magnesium nitride

  8. Answer • d) BaCl2, barium dichloride • The binary compound, BaCl2, is composed of a metal and a nonmetal. Since barium forms only one ion, the name is barium chloride (no prefix is needed).

  9. Question • Which is the correct formula for copper(I) sulfide? a) CuS b) Cu2S c) CuS2 d) Cu2S2 e) None of the above

  10. Answer • b) Cu2S • The copper(I) ion has a +1 charge and the sulfide ion has a −2 charge.

  11. Question • Which of the following is the correct chemical formula for iron(III) oxide? a) FeO b) Fe3O c) FeO3 d) Fe3O2 e) Fe2O3

  12. Answer • e) Fe2O3 • The iron(III) ion has a +3 charge and the oxide ion has a −2 charge.

  13. Question • What is the correct name for this compound with the formula Mg3(PO4)2? a) Trimagnesium diphosphate b) Magnesium(II) phosphate c) Magnesium phosphate d) Magnesium(II) diphosphate e) Magnesium(III) diphosphate

  14. Answer • c) Magnesium phosphate • The magnesium ion has only one possible charge (a +2 charge) and the phosphate ion has a −3 charge.

  15. Question • What is the correct name for this compound with the formula CS2? a) Monocarbon disulfide b) Carbon disulfur c) Carbon disulfide d) Carbon sulfide e) Carbon(IV) sulfide

  16. Answer • c) Carbon disulfide • There is one carbon, but the mono- prefix is not used for the first element. There are two sulfur atoms, so a di- prefix is used. The name ends with an -ide ending.

  17. Question • What is the correct formula for hypobromous acid? a) HBr b) HBrO c) HBrO2 d) HBrO3 e) HBrO4

  18. Answer • b) HBrO • HBrO3 is bromic acid. • Removing one O gives HBrO2 or bromous acid. • Removing one more O gives HBrO or hypobromous acid. • Removing the last O gives HBr or hydrobromic acid.

  19. Question • What is the correct formula for the compound barium hydroxide octahydrate? a) BaOH b) Ba(OH)2 c) Ba(OH)2. 8H2O d) Ba(OH)2(H2O)8 e) BaOH . 8H2O

  20. Answer • c) Ba(OH)2. 8H2O • The barium ion has a charge of +2, so there are two hydroxide groups in the formula. Waters of hydration are written at the end of the formula separated by a dot, with the number of waters of hydration defined using Greek prefixes.

  21. Question • When the equation • NH3 + O2  NO + H2O • is balanced with the smallest set of integers, the sum of the coefficients is • a) 4. • b) 12. • c) 14. • d) 19. • e) 24.

  22. Answer • d) 19. • In order to have the same number of each atom on each side of the equation, we get • 4NH3 + 5O2 4NO + 6H2O • The sum of the coefficients is 19 (4 + 5 + 4 + 6).

  23. Question • How many of the following correctly balance the chemical equation? • CaO + C  CaC2 + CO2 I. CaO + 3C  CaC2 + CO2 II. 2CaO + 5C  2CaC2 + CO2 III. CaO + (5/2)C  CaC2 + (1/2)CO2 IV. 4CaO + 10C  4CaC2 + 2CO2 a) None b) One c) Two d) Three e) Four

  24. Answer • d) Three • Choices II, III, and IV are all correct, although only choice II is written in standard form.

  25. Question • How many of the following statements are true concerning balanced chemical equations? I. The number of molecules is conserved. II. Coefficients indicate mass ratios of the substances involved. III. Atoms are neither created nor destroyed. IV. The sum of the coefficients on the left side equals the sum of the coefficients on the right side. a) None b) One c) Two d) Three e) Four

  26. Answer • b) One • Choice III is the only correct choice.

  27. Question • Which of the following statements is true? a) If a substance is soluble it must be an electrolyte. b) If a substance is an electrolyte it must be soluble. c) Weak electrolytes must be less soluble than strong electrolytes. d) Nonelectrolytes are nonsoluble.

  28. Answer • b) If a substance is an electrolyte it must be soluble. • Electrolytes are substances that dissolve into ions. Not all soluble substances are electrolytes (for example, table sugar is soluble but is not an electrolyte).

  29. Question • Lead(II) nitrate reacts with sodium chloride in aqueous solution to form a precipitate. What is the net ionic equation for this reaction?

  30. Answer • c) Pb2+ (aq) + 2Cl– (aq)  PbCl2 (s) • Both of the reactants are strong electrolytes and completely break up into ions, but the product, lead(II) chloride, is a precipitate. The sodium and the nitrate ions are spectator ions, and so do not appear in the net ionic equation.

  31. Question • Aqueous solutions of sodium sulfide and copper(II) chloride are mixed together. Which statement is correct? a) Both NaCl and CuS precipitate from solution. b) No precipitate forms. c) Only CuS will precipitate from solution. d) Only NaCl will precipitate from solution.

  32. Answer • c) Only CuS will precipitate from solution. • Based on the simple rules for solubility of salts in water, sodium chloride will not form a precipitate, while copper(II) sulfide will.

  33. Question • An aqueous solution of barium nitrate reacts with an aqueous solution of sodium sulfate. Identify the solid and indicate its coefficient in the balanced equation. a) NaNO3, 1 b) BaSO4, 1 c) NaNO3, 2 d) BaSO4, 1 e) None of the above

  34. Answer • b) BaSO4, 1 • Based on the simple rules for solubility of salts in water, barium sulfate will precipitate as a solid. The balanced molecular equation is • Ba(NO3)2 (aq) + Na2SO4 (aq)  BaSO4 (s) + 2NaNO3 (aq)

  35. Question • Which of the following species act as a Brønsted-Lowry base in aqueous solutions? a) CH3COOH b) HCl c) d) All of the above e) None of the above

  36. Answer • c) • A Brønsted-Lowry base accepts a proton in a proton-transfer reaction: • (aq) + H+ (aq)  H2CO3 (aq) • The other species are not even bases (CH3COOH and HCl are acids—they are proton donors).

  37. Question • For the reaction of sodium bromide with chlorine gas to form sodium chloride and bromine, the appropriate half-reactions are (ox = oxidation and re = reduction): a) ox: Cl2 + 2e− 2Cl−re: 2Br− Br2 + 2e− b) ox: 2Br− Br2 + 2e−re: Cl2 + 2e− 2Cl− c) ox: Cl + e− Cl−re: Br  Br+ + e− d) ox: 2Cl− Cl2 + 2e− re: Na+ + e− Na

  38. Answer • b) ox: 2Br– Br2 + 2e– re: Cl2 + 2e– 2Cl– • The conversion of bromide ion to bromine represents an oxidation with the gain of two electrons, while the conversion of chlorine to chloride ion represents a reduction requiring two electrons.

  39. Question • How many of the following are oxidation-reduction reactions? • I. PCl3 + Cl2 PCl5 • II. Cu + 2AgNO3 Cu(NO3)2 + 2 Ag • III. CO2 + 2LiOH  Li2CO3 + H2O • IV. FeCl2 + 2NaOH  Fe(OH)2 + 2NaCl a) None b) One c) Two d) Three e) Four

  40. Answer • c) Two • The answers include • I. where phosphorus undergoes an oxidation from +3 to +5 and chlorine undergoes a reduction from 0 to −1; and • II. where copper undergoes an oxidation from 0 to +2 and silver undergoes a reduction from +1 to 0. • Many redox reactions have an element in its elemental form on one side of the reaction and in a compound on the other side of the reaction.

  41. Question • Which of the following is not an oxidation-reduction reaction? a) A precipitation reaction b) A reaction in which a metal reacts with a nonmetal c) A combustion reaction d) A metal reacting with an acid e) All of the above are oxidation-reduction reactions.

  42. Answer • a) A precipitation reaction • A precipitation reaction represents soluble ions combining to form an insoluble solid with the ions in their same oxidation states. The other possible answers involve elements (in the zero oxidation state) reacting to from ions with nonzero charges.

  43. Question • What are the oxidation numbers of carbon in CO2 and , respectively? a) +2, +6 b) +4, +6 c) −4, −4 d) −4, −6 e) +4, +4

  44. Answer • e) +4, +4 • Using the oxidation state of oxygen in oxide as −2, the carbon must be +4 in order for the resulting CO2 to be neutral, and the carbon must be +4 in order for the to have a −2 charge on the ion.

  45. Question • Which of the following compounds contains nitrogen with the highest oxidation number? a) NH3 b) NO2 c) NCl3 d) N2 e) NO

  46. Answer • b) NO2 • The oxidation states of nitrogen are • NH3 (−3), NO2 (+4), NCl3 (+3), N2 (0), and NO (+2).

  47. Question • Identify the unbalanced reaction • Mg + HCl  MgCl2 + H2 • using the following choices: a) Precipitation reaction b) Acid–base reaction c) Oxidation-reduction reaction d) Combustion reaction

  48. Answer • c) Oxidation-reduction reaction • This particular reaction involves an element changing into an ion and an ion changing into the element, both of which result in changes in the oxidation states of the species.

  49. Question • Each of the following results in a chemical reaction. Which of these is not an oxidation-reduction reaction? a) Methane gas is burned in air. b) Iodine crystals are added to an aqueoussolution of silver nitrate. c) A piece of silver metal is placed in an aqueous solutions of copper(II) nitrate. d) Chlorine gas is bubbled through an aqueous solution of sodium bromide. e) Aqueous solutions of lead(II) nitrate and sodium iodide are mixed together.

  50. Answer • e) Aqueous solutions of lead(II) nitrate and sodium iodide are mixed together. • Choice e) describes a precipitation reaction. The other choices all include elements that become part of a compound.

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