1. MATCHING: Place the letter corresponding to the word(s) being defined in front of each of the

following (12)

_C__ An apparatus for measuring atmospheric pressure.

_R__ The S.I. unit for pressure = 1 N/m²

_M_ An extrastong dipole-dipole attraction of a hydrogen covalently bonded to a very electronegative atom.

_I__ The spontaneous intermingling of one substance with another.

_A__ Description for a noncrystalline solid, i.e. a glass.

_X__ The smallest portions of a crystal that can be repeated over and over in all directions to give the crystal

lattice.

_S__ The conversion of a solid directly into a gas without passing through the liquid state

_D__ The temperature at which the vapor pressure of a liquid equals atmospheric pressure.

_Y__ The resistance of a fluid to a change in its form (to flow)

_V__ The temperature and pressure at which the liquid, solid, and vapor state of a substance can coexist in

equilibrium

_L__The enthalpy change associated with gaseous ions or molecules as they dissolve in water.

_P__ The passage of solvent molecules through a semipermeable membrane

A. Amorphous	G. Crystal	M. Hydrogen bond	T. Surface tension
B. Atmosphere	H. Dialysis	N. London force	U. Torr
C. Barometer	I. Diffusion	O. Manometer	V. Triple
D. Boiling point	J. Effusion	P. Osmosis	W. Vaporization
E. Colloid	K. Fusion	R. Pascal	X. Unit cell
F. Critical	L. Hydration	S. Sublimation	Y. Viscosity

2. MULTIPLE CHOICE: Place the letter(s) corresponding to the best answer(S) on the line in front of

each of the following. (28)

_D___ Of the following gases, the one with the greatest density at STP is

_D___ If a gas’s volume is doubled but the temperature remains constant

_D___ The volume correction term in the van der Waals equation is present because

_D___ The boiling points of the rare gases increases going from He to Xe. The type of intermolecular force

that is most responsible for this trend is

_B___ The intermolecular forces most responsible for the relatively high heat of vaporization for ethanol,

C₂H₅OH are

_A___ The molecules below all have the same number of electrons and nearly equal molecular weights.

Which one is likely to have the highest vapor pressure?

_B___ Bromine, Br₂, has a triple point at -7.3^oC and 44 mmHg and a critical point at 315^oC and 102 atm.

The density of the solid is 3.4 g/cm³, and the density of the liquid is 3.1 g/cm³. When cooled

sufficiently at 40 mmHg, bromine vapor

_A___ Perovskite is a mineral containing calcium, titanium, and oxygen. The unit cell for the mineral has a

Ti ion in the center of the cell, Ca ions at the 8 corners of the cell, and Oxide ions in the 6 faces. The

chemical formula for perovskite is

_D____ The type of crystal that is soft, low melting, and does not conduct electricity is

_B,(C)_ The most water soluble of the following compounds would be

_C___ The lattice energy of SrCl₂ is (–)2114 kJ/mol. The heat of hydration of SrCl₂ (infinite dilution) at

298 K is –2161 kJ/mol. When a very dilute solution of SrCl₂ is prepared, the temperature change

_C___ An ideal liquid solution is prepared having equal mole fractions of two volatile components, A

1. The mole fraction of A = 0.50
2. The mole fractions of A and B are equal, but not necessarily 0.50
3. The mole fractions of A and B are not likely to be equal
4. There will be only one component present, whichever is the solvent

_B___ The aqueous solution with the lowest freezing point of the following group is

_C___ The best method for determining the molecular weight of a relatively large bio-molecule generally

involves measurement of

1. An experiment called for 5.83 L sulfur dioxide SO₂, at 0^oC and 1 atm. What would be the volume of this gas at 25^oC and one atm? T up, V up (4)

PV / T = P’V’ / T’ with P constant; 5.83 L / 273 K = v’ / 298 K

V’ = 5.83 L x 298 / 273 = 6.364 L

V = |__6.36 L____

 

2. An 18.6 ml volume of hydrochloric acid reacts completely with a solid sample of Mg CO₃. The reaction is 2 HCl(aq) +MgCO₃(s) à CO₂ (g) + H₂O(l) + MgCl₂ (aq)

The volume of CO₂ formed is 154 ml at 23^oC and 731 mmHg. What is the molarity of the HCl solution? PV = nRT; n = PV/RT;

18.6 mL/1000 mL/L = 0.0186L; 23^oC + 273 ^o = 296 K (8)

n = [(731 torr/760 torr/atm) x 0.154 L] / [0.08206 Latm/mol deg x 296 K] = 0.0060982 mol CO₂

0.0060982 mol CO₂ x 2 mol HCl/1 mol CO₂ = 0.01296 mol HCl consumed

M = mol/L = 0.012196 mol / 0.0186 L = 0.065572 mol/L

M = |_0.656 M__

3. If it takes 4.67 times as long for a particular gas to effuse as it takes hydrogen under the same conditions, what is the molecular weight of gas? (5)

Since it takes longer for the unknown gas to effuse, it must be heavier than the hydrogen.

Time unknown / Time H₂ = (MW_unk)^0.5 / (MW_H2)^0.5 = 4.67 / 1 = (MW)^0.5 / (2.016)^0.5

(4.67)² / 1² = MW / 2.016

MW = 21.8089 x 2.016 = 43.967

MM = |_ 44.0 g/mol

 

4. Lithium metal has a body center cubic structure with all atoms at the lattice points and a unit cell length of 350.9 pm. Calculate the density (in g/cm³) of lithium? (8)

Bcc = 1/8 x 8 corners + 1 x 1 center = 2 atoms/unit cell

Edge = 350.9 pm x 10^-12 m/pm x cm/10^-2m = 3.509 x 10^-8 cm

D = mass unit cell/ volume unit cell

= [6.941 g/mol x (1 mol/6.022 x 10²³ atoms) x 2 atoms/unit cell]/(3.509 x 10^-8 cm)³

D = 2.305 x 10²³ / 4.3207 x 10^-23 = 0.5335₃ g/cm³

D = |_0.5335 g/cm³

5. The vapor pressure of benzene is 100.0mmHg at 21.6^oC and 400.0 mm Hg at 60.6^oC . What is the DH_Vap for benzene?

21.6 + 273.2 = 294.8; 60.6 + 273.2 = 333.8 (8)

ln (p₁ / p₂) = (DH_vap / R) (1/T₂ – 1/T₁)

= ln 400.0 torr/100.0 torr = (DH_vap /8.314 J/mol deg) (1/294.8 – 1/333.8)

DH_vap = (ln 4.000 x 8.314 J/moldeg) / 3.963 x 10^-4 deg^-1 = (1.2863 x 8.314 J/moldeg) / 3.963 x 10^-4 deg

= 2.908 x 10^-4 J/mol = 29.1 kJ/mol

DH_Vap = |_29.1 kJ/mol_

 

6. Dextran is a polymeric carbohydrate produced by certain bacteria. It is used as a blood substitute. An aqueous solution contains 0.582 g of dextran in 106 ml of solution. It has an osmotic pressure of 1.47 mmHg. What is the average molecular weight of dextran? Assume T = 25^oC (8)

106 mL x 1 L / 1000 mL = 0.106 L; 1.47 torr x 1 atm/760 torr = 0.001934 atm

P = MRT = (n/V)RT = (mass/MW)/V x RT; MW = mass x RT / V x P

MW = [0.582 g x 0.08206 Latm/mol deg x 298] / 0.106 L x 0.001934 atm = 6.942 x 10⁴ g/mol

(if you solve for M instead it = 7.909 x 10^-5 mol; n = M x L = 8.384 x 10^-6 mol;

MW = 0.582 g/ 8.384 x 10^-6 mol)

MM = |_6.94 x 10⁴ g/mol

 

7. An aqueous antifreeze solution is 40.0% ethylene glycol, C₂H₆O_2, by mass The density of the solution is 1.05 g/cm³ Calculate molality, molarity, and mole fraction of ethylene glycol. (15)

MW ethylene glycol = 2(12.01) + 6(1.008) + 2(16.00) = 62.07 g/mol; for H₂O = 18.02 g/mol

The two most straight-forward approaches are :

Assume 1.00 L of solution; 1.05 g/mL x 1000 mL/ L = 1050g/L solution;

1050 g x 40.0/ 100.0 = 420 g E.G.; 1050 – 420 = 630 g H₂O

Mol E.G. = 420 g/62.07 g/mol = 6.767 mol; mol H₂O = 630 g/ 18.02 g.mol = 34.96 mol

(1 mL of solution works similarly but with appropriate change of decimal place)

Assume 100. g soln; 40.0 g E.Gà 40.0 g/ 62.07 g/mol = 0.6444 mol ; 60.0 g H₂O à 60.0/18.02 = 3.330 mol

D = M/V, V = M/D = 100 g solution / 1.05 g/mL = 95.24 mL = 0.09524 L

(1 g of solution works similarly but with appropriate change of decimal place)

molality = mol solute / kg solvent = 6.767 mol / 0.630 kg = 0.6444 mol / 0.0600 kg = 10.74 m

m = |_10.74 molal___

Molarity = mol solute / L solution = 6.767 mol/L = 0.6444 mol/0.9534 L = 6.766 M

M = |_6.77 Molar____

X = mol solute/ mol solution = 6.767 mol /(6.767 + 34.96) mol = 0.644 mol (0.644 mol + 3.330 mol)

= 0.1622

X = |_0.162______

 

8. A solution has a 1:4 mole ratio of pentane to hexane. The vapor pressures of the pure hydrocarbons at 20^oC are 441 torr for pentane and 121 torr for hexane. (8)

1. What are the partial pressures of the two hydrocarbons above the solution?

1 + 4 = 5 mol total

P_T = X_P P_p^o + X_H P_H^o = 1/5(441 torr) + 4/5(121 torr) = 88.2 torr + 96.8 torr = 185.0 torr

P_pentatne = |_88.2 torr___

P_hexane = |_96.8 torr____

2. What is the mole fraction composition of the vapor?