CHAPTER 1:

ELEMENTS AND COMPOUNDS

Elements and Compounds

1-1. Which of the following correctly describes one of the differences between compounds and mixtures?

          (a) compounds contain more than one element but mixtures do not

          (b) compounds have a constant composition but mixtures do not

(c) it is easier to separate the elements in a compound than it is to separate the elements in a mixture

          (d) all of these statements are true

          (e) none of these statements are true.

Answer: (b)

1-2. Describe the difference between the following pairs of symbols.

          (a) Co and CO (b) Cs and CS₂ (c) Ho and H₂O (d) 4 P and P₄

1-3. Describe the difference between the following pairs of symbols.

(a) H and H⁺ (b) H and H^- (c) 2 H and H₂ (d) H⁺ and H^-

Metals versus Nonmetals

1-4. Which of the following elements is neither a metal nor a nonmetal?

          (a) Na (b) Mg (c) Al (d) Si (e) P

Answer: (d)

1-5. Classify the following elements as either metals, nonmetals or semi-metals:

S, Sb, Sc, Se, Si, Sm, Sn, and Sr.

[Note: You might want to give the students AVEE values for these elements and then grade on the basis of their ability to use these data appropriately.]

Ionic versus Covalent Compounds

1-6. Which of the following species contains ions?

          (a) H₂S (b) Cs₂S (c) CsClO₄ (d) SOCl₂

           (e) more than one of the above

Answer: (e)

1-7. Which of the following compounds is composed of molecular ions?

(a) NH₄NO₃ (b) CaO (c) H₂SO₄ (d) NO₂ (e) CO₂

Answer: (a)

1-8. Which of the following is most likely to be an ionic compound?

(a) CS₂ (b) SiC₄ (c) SF₄ (d) SnF₄ (e) SnS

Answer: (d)

1-9. Which of the following should conduct an electric current when dissolved in water?

(I) MgCl₂ (II) CO₂ (III) CH₃OH (IV) KNO₃ (V) Ca₃P₂

          (a) I and II (b) II and III (c) I and IV (d) I, IV and V

          (e) none of the above should conduct an electric current when dissolved in water.

Answer: (d)

1-10. Which of the following won’t conduct electricity?

(I) NaCl(s) (II) HCl(g) (III) HCl(g) in toluene (IV) C₆H₁₂O₆(s)

(a) I (b) I and II (c) I, II and III (d) II and IV

          (e) none of these materials will conduct electricity

Answer: (e)

1-11. Which of the following compounds would you expect to be ionic based on the elements positions in the periodic table?

                     (I) ZnS (II) AlCl₃ (III) BH₃ (IV) H₂S (V) NH₃

           (a) I and II (b) II and III (c) I and IV (d) III, IV and V (e) none of the above

Answer: (a)

1-12. Which of the following compounds should be covalent?

                     (I) CH₄ (II) CO₂ (III) SrCl₂ (IV) NaH (V) SF₄

           (a) I and II (b) II and III (c) I, II and V (d) III, IV and V

          (e) none of the above should be covalent

Answer: (c)

1-13. Which of the following reactions should give an ionic compound?

(I) Mg + O₂ (II) S₈ + F₂ (III) P₄ + Na (IV) Na + Hg (V) K + I₂

          (a) I and II (b) II and III (c) I, II and V (d) I, II, III, and V

          (e) all of the above should give ionic compounds

Answer: (d)

1-14. Which of the following reactions should give a covalent compound?

(I) N₂ + O₂ (II) Cl₂ + F₂ (III) Cl₂ + Cr (IV) S₈ + Na (V) Cu + Sn

           (a) I and II (b) II and III (c) I, II and V (d) I, II, III, and V

          (e) all of the above should give ionic compounds

Answer: (a)

Structure of Atoms

1-15. Calculate the number of silicon atoms in the empirical formula of the mineral beryl, Be₃Al₂(SiO₃)₆.

           (a) 1 (b) 3 (c) 6 (d) 18 (e) 29

Answer: (c)

1-16. Fluoride toothpastes covert the mineral apatite in tooth enamel into fluroapatite, Ca₅(PO₄)₃F. Calculate the number of oxygen atoms in the empirical formula of this compound.

          (a) 1 (b) 3 (c) 4 (d) 12 (e) 21

Answer: (d)

1-17. Which statement correctly describes the difference between the ¹²C, ¹³C and ¹⁴C isotopes of carbon.

          (a) They have the same number of protons but different numbers of electrons.

          (b) They have the same number of neutrons but different numbers of electrons.

          (c) They have the same number of electrons but different numbers of protons.

           (d) They have the same number of protons but different numbers of neutrons.

(e) They have the same number of protons, electrons, and neutrons but different atomic masses.

Answer: (d)

1-18. Which of the following postulates of Dalton's atomic theory is/are still valid today?

                     (I) Matter consists of particles called atoms.

                     (II) Atoms are indestructible and indivisible.

                     (III) All atoms of an element are identical.

                     (IV) Atoms of different elements differ in mass.

(V) When the atoms of different elements combine to form compounds they combine in simple whole number ratios.

          (a) All of these statements are still valid today.

          (b) I and II are still valid, but not III, IV and V.

          (c) I, II and III are still valid, but not IV and V.

           (d) I, IV and V are still valid, but not II and III.

          (e) II and III are still valid, but not I, IV and V.

Answer: (d)

1-19. Calculate the number of protons in the average potassium atom if the atomic weight of potassium is 39 amu and the atomic number of this element is 19.

           (a) 19 (b) 20 (c) 39 (d) 58

          (e) the number of protons is impossible to determine from this information

Answer: (a)

1-20. Calculate the number of electrons on a P^3- ion if the atomic weight of phosphorus is 31 amu and the atomic number of this element is 15.

          (a) 12 (b) 15 (c) 18 (d) 31 (e) 34

Answer: (c)

1-21. Which of the following correctly describes a Zn²⁺ ion that has a mass of 65 amu?

(a) It contains 28 electrons, 30 protons, and 35 neutrons

          (b) It contains 30 electrons, 30 protons, and 35 neutrons

          (c) It contains 32 electrons, 30 protons, and 35 neutrons

          (d) It contains 35 electrons, 35 protons, and 30 neutrons

          (e) It contains 37 electrons, 35 protons, and 30 neutrons.

Answer: (a)

1-22. Which of the following symbols indicates an atom with 12 protons and 10 electrons?

           (a) Mg²⁺ (b) C⁴⁺ (c) O^2- (d) Ne (e) none of these

Answer: (a)

1-23. All of the following have the same number of electrons except:

          (a) K⁺ (b) Ca²⁺ (c) Al³⁺ (d) S^2- (e) Cl^-

Answer: (c)

1-24. What is the formula for the atom or ion that has 26 protons, 30 neutrons, and 24 electrons?

           (a) ⁵⁶Cr²⁺ (b) ⁵⁴Cr²⁺ (c) ⁵⁴Fe²⁺ (d) ⁵⁶Fe³⁺ (e) ⁵⁴Cr

Answer: (c)

1-25. Which of the following atoms have the same number of neutrons?

                     (I) ²³³Th (II) ²³⁵U (III) ²³⁸U (IV) ²³⁸Np

           (a) I and II (b) I, II and IV (c) II and III (d) III and IV

          (e) all of these atoms have the same number of neutrons

Answer: (a)

1-26. Atoms are isoelectronic if they have the same number of electrons, and isobaric if they have the same mass. Which of the following atoms or ions are isobaric?

                     (I) ⁵¹Cr³⁺ (II) ⁵²Cr³⁺ (III) ⁵⁵Mn³⁺ (IV) ⁵⁹Ni⁴⁺ (V) ⁵⁹Co³⁺

          (a) I and II (b) II and III (c) III and IV (d) IV and V

          (e) III, IV and V

Answer: (c)

Predicting the Formulas of Compounds

1-27. Fluoride toothpastes convert the mineral apatite in tooth enamel into fluoroapatite, Ca₅(PO₄)₃F. If fluoroapatite contains Ca²⁺ and PO₄^3- ions, what is the charge on the fluoride ion in this compound?

          (a) +1 (b) 0 (c) -1 (d) -2 (e) -3

Answer: (c)

1-28. Aluminum chlorhydrate is added to antiperspirants to stop people from sweating. If this compound contains neutral H₂O molecules and Al³⁺, OH^-, and Cl^- ions, and the formula of this compound is Al_x(OH)₅Cl ⋅ 2 H₂O, what is the value of x in this formula?

          (a) 0.5 (b) 1 (c) 1.5 (d) 2 (e) 3

Answer: (d)

1-29. Verdigris is a green pigment used in the manufacture of paint. The simplest formula for this compound is Cu₃(OH)₂(OAc)₄. What is the charge on the copper ions in this compound if the other ions are the OH^- (hydroxide) and OAc^- (acetate) ions?

          (a) -2 (b) 0 (c) +1 (d) +2 (e) +3

Answer: (d)

1-30. What is the empirical formula for the compound of strontium and phosphorus?

          (a) SrP (b) SrP₂ (c) Sr₂P (d) Sr₂P₃ (e) Sr₃P₂

Answer: (e)

1-31. Predict the formulas for neutral compounds containing the following pairs of ions.

(a) Mg²⁺ and NO₃^- (b) Fe³⁺ and SO₄^2- (c) Na⁺ and CO₃^2-

Answer: Mg(NO₃)₂; Fe₂(SO₄)₃; Na₂CO₃

1-32. Predict the formulas for neutral compounds containing the following pairs of ions.

          (a) H⁺ and O₂^2- (b) Zn²⁺ and PO₄^3- (c) K⁺ and PtCl₆^2-

Answer: H₂O₂; Zn₃(PO₄)₂; K₂PtCl₆

1-33. What is the formula of the neutral compound formed when phosphorus reacts with sulfur if phosphorus is in the +5 oxidation state and sulfur is in the -2 oxidation state?

          (a) PS (b) PS₂ (c) PS₃ (d) P₂S₅ (c) P₅S₂

Answer: (d)

1-34. If the formula for magnesium nitride is Mg₃N₂, what would be the formulas for potassium nitride and aluminum nitride?

Answer: K₃N; AlN

1-35. Compounds that contain the O^2- ion are called oxides; those that contain the O₂^2- ion are called peroxides. If the formula for potassium oxide is K₂O, what would be the formula for potassium peroxide?

          (a) KO (b) K₂O (c) KO₂ (d) K₂O₂ (e) KO₂

Answer: (d)

1-36. What is the charge on the [Co(NO₂)₆^x] ion if this complex ion is formed by combining Co³⁺ and NO₂^- ions?

          (a) +3 (b) 0 (c) -3 (d) -6 (e) -12

Answer: (c)

1-37. Honda and Toyota both sell hybrid cars that have engines that can run on either gasoline or electricity stored in a battery. (Both companies are “losing their shirts” on these cars because so few are being sold.) The advantage of hybrid cars is simple: Totally electric cars need batteries that weigh almost as much as the vehicle!) It isn’t surprising that a high priority is the search for better batteries. Barium ferrate (BaFeO₄) is being tested for use in batteries. Use the positions of barium and oxygen in the periodic table to predict the oxidation state of the iron atom in this so-called “super-iron” compound.

(a) +2 (b) +3 (c) +4 (d) +6 (e) +8

Answer: (d)

1-38. When Apple™ released its Powerpoint™ laptop there was a problem with some of the lithium ion batteries catching fire. One of the compounds being studied for use as an electrode in lithium ion batteries being developed for use in the next generation of portable computers has the following empirical formula: LiMnO₄. What is the oxidation state of the manganese atom in this compound?

(a) +2 (b) +3 (c) +4 (d) +5 (e) +7

Answer: (e)

1-39. The active ingredient in Rolaids has the formula NaAl(OH)₂CO₃. Calculate the oxidation state of the aluminum atom in this compound.

          (a) -3 (b) 0 (c) +1 (d) +2 (e) +3

Answer: (e)

1-40. Only 15% of the energy a gallon of gasoline is used to move a vehicle. It isn’t surprising that batteries are being developed to store more energy on-board the vehicle and to use the energy more efficiently. Two directions in which the search is going are lithium ion and nickel metal hydride batteries. Lithium ion batteries are high energy density, 3.6 V batteries that use a lithium salt such as LiCoO₂ or LiPF₆ for the positive electrode, or cathode. Use the positions of lithium and fluorine in the periodic table to predict the oxidation state of the phosphorus atom in LiPF₆.

(a) +1 (b) +2 (c) +3 (d) +4 (e) +5

Answer: (e)

1-41. When we talked about “nitrous oxide” or “laughing gas” in class I noted that it has been used as an anaesthetic for short operations — less than 45 minutes. The problem with nitrous oxide was illustrated in the movie The Little Shop of Horrors, in which Steve Martin demonstrated that long-term exposure to this gas does not produce laughter (or hysteria). It can be fatal. Several years ago, the Chronicle of Higher Education reported that a junior at MIT “borrowed” a cylinder of nitrous oxide, took it to his room, and was found dead the next morning. If the formula for this compound is N₂O, what is the best name for the compound?

          (a) nitrogen monoxide (b) nitrogen dioxide (c) dinitrogen monoxide

          (d) nitrogen peroxide (e) “Steve”