Answers to Critical Thinking Questions
for
C HEMISTRY
A Guided Inquiry
Seventh Edition, 2017
Richard S. Moog
Franklin & Marshall College
John J. Farrell
Franklin & Marshall College
Latest Update: June 20, 2018
John Wiley & Sons, Inc.
Answers to Critical Thinking Questions
Please do not give these answers to students.
Quite often, the answers given here are less detailed than what is expected for a student’s answer.
ChemActivity 1
1. 1H—, 13C— , 16O2— , 23Na+ 2. 1H, 2H, 12C, 13C
3.
# of protons
# of neutrons
# of electrons
charge
12C 6 6 6 0
13C 6 7 6 0
13C— 6 7 7 –1
4. a) The diagram indicates that each C atom has 6 protons.
b) The diagram indicates the number of neutrons for each of the species.
c) Counting the black dots for each C species 5. a) All carbon atoms and ions have six protons.
b) The only column in the table in CTQ 3 that has the same value for all entries is the column indicating the number of protons.
6. a)
# of protons
# of neutrons
# of electrons
charge
1H 1 0 1 0
2H 1 1 1 0
1H— 1 0 2 –1
b) All hydrogen atoms and ions have one proton. The only column in the table that has the same value for all entries is the column indicating the number of protons.
7. Z is the number of protons in the nucleus of that atom (or ion).
8. There are twenty-eight protons in the nucleus of a Ni atom.
9. a) The atom has 7 electrons (a total charge of -7) and 6 protons (a total of +6). The net charge on the atom is, therefore, -1.
b) In an ion the number of protons and electrons are not equal whereas in a neutral atom the number of protons and number of electrons are equal.
c) The charge on an ion = # of protons – # of electrons.
10. a) 12C, 13C
b) For different isotopes, the number of neutrons are not the same; for example, the isotope 12C has 6 neutrons whereas the isotope 13C has seven neutrons.
11. a) For 13C– the mass number is 13.
b) The mass number (A) is the sum of the number of protons and the number of neutrons in the nucleus of an atom.
12. All H atoms and ions must have one proton. The mass number is 1, so the sum of protons and neutrons is 1. Given that there is 1 proton, the number of neutrons must be 0. The charge is +1; therefore, there must be one more proton than electrons.
Because there is 1 proton, the number of electrons must be 0.
13. The O atom has 8 protons. The mass number is 16; so there are 16 – 8 = 8 neutrons.
The charge on the atom is –2; so there are 8 – (– 2) = 10 electrons. The Na atom has 11 protons. The mass number is 23; so there are 23 – 11 = 12 neutrons. The charge on the atom is +1; so there are 11 – (+1) = 10 electrons.
14. Most of the mass is in the nucleus—where the protons and neutrons are. Note that the difference in mass between a 13C and a 13C– atom (which differ by only one electron) is only 0.0005 amu. Thus, the electron has very little mass compared to the total mass of each atom.
ChemActivity 2
1. None of the individual marbles has the same mass as the average mass.
2. The method just above equation 2 should be used because we know the percentages of each type of marble.
3. There are 3 isotopes (the percentages add up to 100%).
4. All isotopes of magnesium have twelve protons in the nucleus. The three isotopes of magnesium have 12, 13, and 14 neutrons in the nucleus.
5. 12.0000 amu
6. a) 12000.0 amu; b) 13003.4 amu
7. Slightly more than 12000.0 amu because 12000.0 amu would be the minimum and it is very likely that there will be at least one and probably several 13C atoms present among the 1000 atoms. Given that the isotopic abundance of 13C is 1.11%, on average there should be about 1113C atoms (.0111 x 1000 = 11.1) present in a sample of 1000 C atoms.
8. a) You must know the total number of items to use the first method. The second method is preferred because we know the percentages (isotopic abundances) of Cl.
b) 0.7577 × 34.9689 amu + 0.2423 × 36.9659 amu = 35.45 amu.
c) Zero. No chlorine atoms have the average mass.
9. a) 35.45 amu. b) 5.887 x 10–23 g 10. 5.887 x 10–23 g × 6.022 x 1023 = 35.45 g 11. a) 24.31 amu. b) 4.037 x 10-23 g 12. 4.037 x 10–23 g × 6.022 x 1023 = 24.31 g 13.
Average Mass of one atom in amu
Average Mass of one atom in grams
Average Mass of 6.02 x 1023 atoms in grams
Cl 35.45 5.887 x 10–23 35.45
Mg 24.31 4.037 x 10-23 24.31
14. a) It is the same number. b) It is the same number.
15. a) It is the same number. b) It is the same number.
Answers to Exercises and Problems
for
C HEMISTRY
A Guided Inquiry
Seventh Edition, 2017
Richard S. Moog
Franklin & Marshall College
John J. Farrell
Franklin & Marshall College
Latest Update: December 20, 2017
John Wiley & Sons, Inc.
Answers to Exercises and Problems
These answers may be provided to students at the instructor’s discretion.
Do not post on publicly available website.
These answers do not contain full explanations or solutions.
ChemActivity 1 Exercises
1.
2. 1.674 × 10–24 g. 1.993 × 10–23 g.
3. 8.67 × 10–17 g.
4. 12.00 g.
5. 2.6621 × 10–23 g.
6. a) The mass number is the sum of the number of protons and the number of neutrons in the nucleus. b) The atomic number is the number of protons in the nucleus.
7. False. 18O has 8 protons and 10 neutrons.
8.
Species Electrons Protons Neutrons
24Mg 12 12 12
23Na+ 10 11 12
35Cl 17 17 18
35Cl- 18 17 18
56Fe3+ 23 26 30
15N 7 7 8
16O2- 10 8 8
27Al3+ 10 13 14
9.
Isotope Atomic
Number Z
Mass Number
A
Number of Electrons
59Co2+ 27 59 25
14N 7 14 7
7Li 3 7 3
6Li 3 6 3
58Zn2+ 30 58 56
19F– 9 19 10
Isotope Atomic
Number Z
Mass Number
A
Number of Electrons
31P 15 31 15
18O 8 18 8
39K+ 19 39 18
58Ni2+ 28 58 26
10. All isotopes of an element have the same number of protons in the nucleus. One isotope of an element is differentiated from another isotope of the same element by the number of neutrons in the nucleus.
Problems
1. Using carbon-13 and carbon-12, approx mass of neutron = 13.0034 – 12 = 1.0034 amu.
approx mass of 14C = 13.0034 + 1.0034 = 14.0068 amu.
2. a) Using 14C and 14C–, mass of electron is approximately 13.0039 amu – 13.0034 amu = 0.0005 amu
b) Using 1H, mass of proton is approximately 1.0078 amu – 0.0005 amu = 1.0073 amu c) Using 1H and 2H, mass of neutron is approximately 2.0140 amu – 1.0078 amu =
1.0062 amu
(Note that slightly different values for the masses of protons and neutrons will be obtained if different elements/isotopes are used to calculate these masses.)
3. The calculated mass of 12C based on the masses of the constituent particles is 12.099 amu;
and the actual mass of 12C is exactly 12 amu.
ChemActivity 2 Exercises
1. a) 1.008 g. b) 39.10 g.
2. a) 45.98 g. b) 57.27 g.
3. Isotopes are versions of atoms of an element that have the same number of protons in the nucleus but differ in the number of neutrons that they have.
4. 37Cl has two more neutrons in its nucleus.
5. average mass of a marble = (1 × 5.00 g + 3 × 7.00 g)/4 = 1
4 × 5.00 g + 3
4 × 7.00 g = 0.2500 × 5.00 g + 0.7500 × 7.00 g = 6.50 g (this is eqn (2))
6. 10.44 amu
7. 35Cl, 75.76%. 37Cl, 24.24%.
8. a) 4.003 g b) 39.10 g
9. a) 1 He atom × × 4.003 g He/mole He atoms = 6.647 × 10–24 g of He.
b) 1 K atom × × 39.098 g K/mole K atoms =
6.493 × 10–23 g. of K 10. 60.06 g
11. 3.613 × 1024 atoms.
12. 2.619 × 1024 atoms.
13. a) 3.029 × 1025 atoms. b) 1.022 × 1019 atoms. c) 1.878 × 1025 atoms. d) 9.782 × 1027 atoms.
14. Phosphorus 15. 89.5 g I
