CH 5, 7, 8, 9 Assessment 2009-2010

1. Answer the following using chemical concepts and principals of the behavior of gases.

(a) A metal cylinder with a volume of 5.25 L contains 3.22 g of He(g) and 11.56 g of N2 (g) at 15.0°C.

(i) Calculate the total pressure in the cylinder.

(ii) Calculate the partial pressure of N2 in the cylinder.

(b) A 1.50 L container holds a 9.62 g sample of an unknown gaseous saturated hydrocarbon at 30.0°C and 3.62 atm.

(i)Calculate the density of the gas.

(ii)Calculate the molar mass of the gas.

(iii)Write the formula of the hydrocarbon.

(iv)Calculate the root mean square velocity of the gas molecules in the container at 30.0°C.

**Note 1 J = 1 kg · m2 s-2

2. Answer each of the following using principles of atomic or molecular structure.

(a) Explain why the H—O—H bond angle in H2O is less than the H—N—H bond angles in NH3.

(b) Explain why the radius of the Br atom is less than the radius of the Br1- ion.

(c) Explain why the dipole moment of HI is less than the dipole moment of HCl.

3. Answer the following questions related to sulfur.

(a) Consider the atom sulfur, and its ion, sulfide.

(i) Draw the orbital diagram for the atom AND the ion.

(b) Name the atom that is isoelectronic with the sulfide ion.

(i) Would it be easier to remove an electron from the sulfide ion, or from the isoelectronic

atom? Explain.

4. Draw complete Lewis Dot Diagrams for the molecules CH4, PF5 and SF4. Identify the bond angle, hybridization of the central atom and geometric (VSEPR) shape of each molecule.

5. There are two Lewis structures possible for the molecule OPF3. In one structure there are 4 sigma bonds on the central phosphorus atom, and on the other, there are 4 sigma bonds and one pi bond. Which structure would best represent this molecule? Justify your answer in terms of formal charge.

Directions: Each set of lettered choices below refers to the numbered statements immediately following it. Select the one that is best in each case and then place the letter of your choice on your answer sheet. A choice may be used more than once, or not at all in each set.

Questions 1-3 refer to the following molecules.

(A) CO

(B)CH4

(C)HF

(D)PH3

(E)F2

  1. Contains two π-bonds
  2. Has the highest dipole moment
  3. Has the molecular geometry that is trigonal pyramidal.

Questions 4 through 7 refer to neutral atoms with the following electron configurations.

(A)1s2

(B)1s22s12p1

(C)1s22s22p3

(D)1s22s22p6

(E)[Ar]4s23d8

  1. Is in an excited state.
  2. Has exactly five valence electrons.
  3. Has the highest first ionization energy.
  4. Forms an aqueous cation that has color.
  1. Of the following gases, which has the greatest average molecular speed at 298K?

(A)Cl2

(B)NO

(C)H2S

(D)HCN

(E)PH3

  1. Types of hybridization exhibited by the carbon atoms in a molecule of propyne, CH3CCH, include which of the following?
  1. sp
  2. sp2
  3. sp3

(A)I only

(B)III only

(C)I and III only

(D)II and III only

(E)I, II and III

  1. In which of the following are the chemical species correctly ordered from the smallest to the largest radius?

(A)B < C < N

(B)Ar < Xe <Kr

(C)Cl < S < S2-

(D)Na < Na+ < K

(E)K+ < Ca2+ < K

8H2(g) + S8(s)  8H2S(g)

  1. When 25.6 g of S8(s) (molar mass of 256 g/mol) reacts completely with excess H2(g) according to the equation above, the volume of H2S(g), measured at 0.0°C and 1.00 atm, produced is closest to

(A)30L

(B)20L

(C)10L

(D)5L

(E)2L

CS2(l) + 3O2(g)  CO2(g) + 2SO2(g)

  1. When 0.60 mol of CS2(l) reacts as completely as possible with 1.5 mol of O2(g) according to the equation above, the total number of moles of reaction products is

(A)2.4 mol

(B)2.1 mol

(C)1.8 mol

(D)1.5 mol

(E)0.75 mol

  1. At approximately what temperature will 40.0 g of argon gas at 2.0 atm occupy a volume of 22.4 L?

(A)1,200 K

(B)600 K

(C)550 K

(D)270 K

(E)140 K

  1. At which of the following temperatures and pressures would a real gas be most likely to deviate from ideal behavior?

(A)100 K and 50 atm

(B)200 K and 5 atm

(C)300 K and 0.01 atm

(D)500 K and 0.01 atm

(E)500 K and 1 atm

Ionization Energy (kJ/mol)

1st / 2nd / 3rd / 4th / 5th / 6th / 7th
787 / 1580 / 3200 / 4400 / 16000 / 20000 / 24000
  1. The first seven ionization energies of element X are shown in the table above. On the basis of these data, element X is most likely a member of which of the following groups (families) of elements?

(A)Alkaline earth metals

(B)Boron group

(C)Carbon group

(D)Nitrogen group

(E)Halogen group