Introductory Chemistry

Introductory Chemistry

 

1. The element mercury has seven naturally occurring isotopes. Based on the isotopic masses and abundances shown below, calculate the average atomic mass of

mercury.
Isotope Mass (amu) Abundance (%)
196Hg 195.9658 0.146
198Hg 197.9668 10.02
199Hg 198.9683 16.84
200Hg 199.9683 23.13
201Hg 200.9703 13.22
202Hg 201.9706 29.80
204Hg 203.9735 6.85
2. Dieldrin is an insecticide composed of carbon, hydrogen, oxygen, and chlorine. A 2.416 g sample of dieldrin is subjected to combustion analysis, yielding 3.350

g CO2and 0.458 g H2O. Mass spectrometry gives a molecular weight of 381 g mol-1. From a separate experiment, it is found that there are 2:1 ratio of C:Cl atoms. Based

on this information, what is the molecular formula of dieldrin?
3. An iron sulfide contains 36.5% S by mass. The iron sulfide is heated in an atmosphere of pure oxygen, which produces SO2(g) and an iron oxide containing 27.6%

O by mass.
a. Write a balanced equation for the reaction.
b. If 1.0 kg of the iron sulfide reacts with excess oxygen, what is the theoretical yield of the iron oxide?
4. In the manufacture of Portland cement, limestone (CaCO3(s)) is decomposed into lime (CaO(s)) and CO2(g), in a kiln. Use data from Appendix II, part B in your

textbook to calculate how much heat is required to decompose 2.70 × 103 kg of limestone. (Assume that the heats of reaction are temperature independent.)
5. Hydrogen gas can be produced from natural gas, which is primarily composed of methane (CH4). Determine ?rH° for the following reaction, given the reaction

enthalpy data shown in the table below.
CH4(g) + ½ O2(g) ? CO(g) + 2H2(g)
Reaction ?rH° (kJ mol-1)
CH4(g) + 2O2(g) ? CO2(g) + 2H2O(g) -802
CH4(g) + CO2(g) ? 2CO(g) + 2H2(g) +247
CH4(g) + H2O(g) ? CO(g) + 3H2(g) +206
6. A 1.500 L flask is filled with a mixture of 1.20 g H2 and 8.40 g O2, at 25°C. The mixture is ignited, and hydrogen and oxygen combine to form water.
a. What is the total pressure inside the flask before the reaction? (Report your answer in units of atmospheres.)
b. What is the total pressure after the reaction, once the flask is returned to 25°C? (Vapour pressure of water at 25°C is 23.8 mm Hg.)
7. Draw an energy-level diagram that shows all of energy levels from n = 5 to n = 1. Draw all possible emission lines between these levels. In your diagram,

ensure that the energy levels are spaced correctly (e.g. according to the Bohr model).
8. In the photoelectric effect, the work function is the energy that must be supplied to overcome the attractive forces that hold an electron in the metal. For

mercury, the work function is equal to 435 kJ mol-1 of photons. What is the kinetic energy, in joules, of the ejected electrons when light with a wavelength of 220 nm

strikes the surface of mercury?

 

 

1. Construct a Born-Haber cycle to calculate the lattice energy of MgCl2. (Use data from Appendix II, Table 8.1, Figure 8.15 and Figure 9.4 of the textbook.)
The CRC Handbook of Chemistry and Physics lists the MgCl2 lattice energy as 2540 kJ mol-1. How does your answer compare to the literature value?
(Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 86th edition. Taylor & Francis, Boca Raton, 2005.)
2. Explain, in detail, why atomic radii do not increase uniformly with increasing atomic number. Give specific examples in your answer.
3. Hydrogen azide (HN3) is a shock-sensitive liquid, which means it explodes when subjected to a physical shock. The HN3 molecule contains two N-N bonds with bond

lengths 113 pm and 124 pm. The H-N-N bond angle is 112°. Draw two Lewis structures of HN3 that obey the octet rule. What is the formal charge of each atom in your

structures? Which structure is most consistent with the experimental data?
4. Consider the following structural data on fluorine nitrate, FONO2. Using this data, construct a Lewis structure and a three dimensional drawing of the

molecule. Describe the bonding in terms of valence bond theory (i.e. orbital hybridizations and orbital overlaps to form s and p bonds).
Bond* Bond length (pm)
N-O 129
N-O’ 139
F-O’ 142
5. *O’ refers to the oxygen atom bonded to fluorine.
6. Bond angles:
O-N-O = 125°
F-O’-N = 105°
7. The NO’F plane is perpendicular to the O2NO’ plane.
8. The anion I42- is linear. The anion I5- is bent, with a 95° angle at the central iodine atom. Draw valid Lewis structures for each of these ions.
9. A 50.0 g piece of CO2(s) (i.e. “dry ice”) is sealed inside a 0.250 L container held at 20°C. Based on the phase diagram of CO2 (Figure 11.42 in the textbook),

what state(s) of matter are present inside the container?
10. The ethanol content of alcoholic beverages is sometimes expressed in terms of “proof.” This term comes from a 17th century test for the alcohol content in

whiskey. The whiskey was poured onto gunpowder and then set on fire. If the whiskey was too wet, the gunpowder would not ignite after the whiskey had burned off.

However, if the whiskey had not been watered down, the gunpowder would ignite. A positive test required a minimum ethanol content of approximately 50% ethanol (by

volume), which was called “100 proof.” Whiskey with 40% ethanol is “80 proof,” and so on.
a. What is the approximate molar concentration of ethanol in 100-proof whiskey? Treat the whiskey as a solution of ethanol dissolved in water. The density of pure

ethanol is 0.789 g mL-1. Assume the density of the mixture is the same as that of the solvent. Report your answer to two significant figures.
b. If the vapour pressure of water is 17.5 torr at 20°C, what is the water vapour pressure inside a bottle of 100 proof whiskey?
11. What is the freezing point of a 50% by volume ethanol solution? Assume water is the solvent. (Use data from Table 12.7 in the textbook.)