Arrange the following in order from highest to lowest boiling point, using the c

Question

Arrange the following in order from highest to lowest boiling point, using the concept of intermolecular forces to prove your answer: CH_2Cl_2, NH_2, H_2O, CO_2 A 2 liter flask at 20 degree C contains 4.5 grams of CH_2Cl_2 (vapor pressure = 329 mm Hg). How many grams of liquid will remain in the flask after the liquid-vapor equilibrium is established? The vapor pressure of SiCl_4 is 100 mm Hg at 5 degree C and the compound has a normal boiling point of 58 degree C. What is the enthalpy of vaporization for SiCl_4? Sodium has a density of 0.971 g/cm^2 and crystallizes in a body-centered cubic unit cell. What is the atomic radius of sodium? What is the energy of crystallization for Na_() + 1/2 H_2() not NaH_() (Delta H_f^o = -60 kJ/mol), given: Delta H_vap degree Na = +107.3 kJ/mol, E_bond H_2 = +436 kJ/mol, E_ion Na = +496 kJ/mol and E_ion H = -73 kJ/mol. A solution of NaCl in water has a density of 1.025 g/mL and is 3.50% NaCl be mass, determine: a) The molarity of the solution b) the molality of the solution c) Z_NaCl What is the concentration of O_2(g) in water under 1 atmosphere total pressure of air given a Henry's law solubility of 2.21 times 10^-3 M/atm for oxygen and the fact that chi_o2 in air = 0.21? What is the vapor pressure of a solution containing 5.00 grams C_7H_6O_2 in 100 grams of C_2H_6O (P' = 100.5 mm Hg)? How many grams of CH_4NH_2O are dissolved in a solution containing 150 grams of water which freezes at -2.07 degree C? (k_f H_2O = -1.86 degree C/m) A 200 mL solution containing 1.5 grams of an unknown at 25 degree C exhibits and osmotic pressure of 407 mm Hg. What is the molar mass of the unknown?

Explanation / Answer

a) The boiling point increases with increase in intermolecular interactions

H2O has stronger hydrogen bond so it will have highest boiling point

Then it will be NH3 : london dispersion force, dipole dipole force and also hydrogen bond

Then it will be CH2Cl2 : london dispersion forces , dipole dipole force and no hydrogen bond

CO2: no dipole -dipole interaction

Answer: H2O > NH3 > CH2Cl2 > CO2.

b) The amount of vapour at equilibrium will be calculated using ideal gas law

PV = nRT

n = PV / RT

R= 0.0821 L atm / mol K

T = 20C = 273. + 20 =293 K

P = 329 mmHg = 329/760 atm = 0.433 atm

V = 2L

n = moles = 0.433 X 2 / 0.0821 X 293 = 0.036 moles

Mass = Moles X molecular weight = 0.036 X 85 = 3.06 grams

so the amount left = 4.5 - 3.06 grams liquid = 1.44 grams

c) We will use Clapeyron Clausius equation

ln (P2/P1) = [DeltaH / R ][1/T1 - 1/T2 ]

P2 = 100mmHg P1 = 760 mmHg

T2 = 50C = 278 K

T1 = 58 0C = 273 + 58 = 331 K

DeltaH = ?

R = 8.314 J /mol K

ln (100/760) = DeltaH / 8.314 [ 1/ 331 - 1 / 278]

-2.028 X 8.314 = DeltaH [0.003021 - 0.003597] = DeltaH (-0.03295)

DeltaH = 511.71 Joules / mole

d) Density = Z X M / Na X a^3

a^3 = Z X M / Na X Density

Z = 2 [For BCC]

M = atomic weight = 23 g / mole

Na = Avagadro's number = 6.023 X 10^23

Dentsity = 0.971 g / cm^3

a^3 = 2 X 23 / 6.023 X 10^23 X 0.971 = 7.865 X 10^-23

a = 4.28 X 10^-8 cm

For BCC , a = 4R / (3)^1/2

R = radius = a ((3)^1/2 ) / 4 = 1.853 X 10^-8 cm

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