Answers to the Chemistry Fall Exam Review Questions

Q1. What are the differences between a mixture and a compound?

A1. Mixtures can be separated into their components by physical means. Compounds can be separated into their components only by chemical means.

Q2.  What must occur for a process to be a chemical reaction?

A2. The process must involve a change in chemical properties.

Q3. Which group of measurements is the most precise?  (Each group of measurements is for a different object. (A) 2 g, 3 g, 4 g  (B) 2 g, 2.5 g, 3 g  (C) 2.0 g, 3.0 g, 4.0 g  (D) 1 g, 3 g, 5 g  (E) 2.0 g, 3.0 g, 4.0 g, 5.0 g

A3. (B) 2g, 2.5g, 3g

Q4. When multiplying and dividing measured quantities, the number of significant figures in the result should be equal to the number of significant figures in _____.

A4. The least precise measurement

Q5. What a correct conversion factor for changing:

(a) kilometers to meters?

A5. 1000 m = 1 km

(b) grams to micrograms?

A5. 1 g = 1 x 106 µg

(c)liters to centiliters?

A5. 1 L = 100 cL

Q6. The density of osmium, which is the densest metal, is 22.57 g/cm³.  What is the mass of a block of osmium that measures 1.00 cm x 4.00 cm x 2.50 cm?

                 M               M = DV
A6. D = ------                  = (22.57 g/cm3)(1cm x 4 cm x 2.5 cm)
                 V                     = 226 g

Q7.  What are the components of Dalton's atomic theory?

A7. All elements are composed of tiny indivisible particles called atoms. Atoms of the same element are identical. Atoms of different elements are different.

Atoms of different elements can physically mix together or change chemically by combining in simple whole number ratios to form compounds. Chemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element never change into atoms of another element by chemical reactions.

Q8. How do the isotopes hydrogen-1 and hydrogen-2 differ?

A8. Hydrogen-1 has no neutrons.

       Hydrogen-2 has one neutron.

Q9. Why do chemists use relative comparisons of masses of atoms?

A9. The actual mass of protons and neutrons is very small.

Q10.  Isotopes of the same element have different _____.

A10. mass number

Q11. If E is the symbol for an element, which two of the following symbols represent isotopes of the same element?

(A) 20    (B) 20    (C) 21    (D) 21
         E            E            E            E
    10        11         9        10

A12.(A) 20      (D) 21
                 E  and       E
            10          10

Q12.  Consider an element Z that has two naturally occurring isotopes with the following percent abundances: the isotope with a mass number of 20 is 25% abundant; the isotope with a mass number of 22 is 75% abundant. What is the average atomic mass for element Z?

A12. 20 x 0.25 =    5 g
        22 x 0.75 = 16.5 g
                           --------
                           21.5 g

Q13. Which subatomic particle plays the greatest part in determining the Physical and chemical properties of an element?

A13. electron

Q14. The modern periodic table is arranged in order of increasing atomic ____.

A14. number

Q15. In any chemical compound, the elements are always combined in the same proportion by ___.

A15. mass

Q16. Which of the following formulas represents:

(a) an ionic compound?(A)BaI₂ (B) N₂O₄ (C)Kr  (D)CS₂ (E) PCl_3.

A16a. (A) BaI₂

(b) a molecular compound? (A) Xe (B)SO₂ (C) BeF₂ (D)ZnO (E) Mg₃N₂

A16b. (B)SO₂

(c) binary molecular compound? (A) BeHCO₃ (B) PCl₅ (C)AgI (D)MgS (E)Cr₂O₃>

A16c. (B) PCl₅

(d) When naming acids, the prefix hydro- is used when the name of the acid anion ends in _____.

A16d. “-ide”

Q17. (a) When Group 2 elements form ions, they ___ two electrons.

A17a. lose

(b) The nonmetals in Group 17 _____ one electron when they form ions.

A17b. gain

Q18. (a) An -ite or -ate ending on the name of a compound indicates that the compound _____.

A18a. contains a polyatomic ion

(b) Ternary ionic compounds contain three different _____.

A18b. elements

Q19. Which of the following compounds contains the lead(IV) ion? (A)PbO₂ B)PbCl₂ (C)Pb₄O₃ (D)PbO (E)Pb₂O

A19. (A) PbO₂

Q20.  The lowest whole-number ratio of the elements in a compound is called the _____.

A20. empirical formula

Q21. (a) The molar volume of a gas at STP occupies _____.

(a) 22.4 L

(b) What combination of temperature and pressure correctly describes standard temperature and pressure, STP?

(b) 0 ºC (273 K) and 1 atm (101.3 kPa)

Q22. Which of the following compounds has the lowest percent gold content by weight?(A) AuCl₃ (B) AuBr₃ (C)  AuI₃ (D)  Au(OH)₃ (E) AuOH

A22. (C)  AuI3

Q23.  Find the mass in grams of 2.20 x 10²³ molecules of F2.

A23.

     2.20 x 10²³ molecules F₂                       1 mol F₂                                        38.05g F₂
------------------------------------ X  --------------------------- X  --------------- = 13.9 g F₂
               1                                         6.02 x 10²³ molecules F₂                   1 mol F₂

Q24.  How many kilograms of aluminum can be recovered from 429 kg of the ore, Al₂O₃?

A24. Al: 27.0 x 2 =  54.0 g                              54.0 g
          O: 16.0 x 3 =  48.0 g                  %Al = -------- = 52.9%
                                --------                             102.0 g
                                 102.0 g

         (429 kg)(0.529) = 227 kg Al

Q25.  What is the percent composition of NiO, if a sample of NiO with a mass of 10.3 g contains 8.1 g Ni and 2.2 g O?

                      8.1 g
A25. %Ni = -------- X 100% = 79 % Ni
                     10.3 g

                    2.2 g
        %O = -------- X 100% = 21 % O
                    10.3 g

Q26. Describe the different principles that govern the building of an electron configuration.

A26. The Aufbau principle states that electrons enter the orbitals of lowest energy first.  The Pauli exclusion principle states that each orbital can hold only two electrons.  Hund's rule states that electrons first enter separate orbitals of the same energy, with each electron having the same spin, before sharing an orbital or having different spins.

Q27. What is the quantum mechanical model?

A27. It is a model that describes the motions of electrons in atoms as probabilistic motions within a certain region.  It is depicted as electron clouds, the density of which represents the probability of finding the electron in that region.  The electron cloud of the quantum mechanical model is centered on the atomic orbital as proposed by Bohr.

Q28. Explain why it takes more energy to remove a 4s electron from zinc than from calcium.

A28. Electrons occupy orbitals in a definite sequence, filling orbitals with lower energies first.  Generally, orbitals in a lower energy level have lower energies that those in a higher energy level, but in the third level the energy ranges of the principal energy levels begin to overlap.  As a result, the 4s sublevel is lower in energy than the 3d sublevel, so it fills first.