Random
What IMF is present in N₂?
London dispersion forces (nonpolar molecule).
Define molality.
Mol solute / kg solvent.
Write the Clausius-Clapeyron equation.
ln(P₂/P₁) = -∆Hvap/R × (1/T₂ - 1/T₁)
Write the Clausius-Clapeyron equation.
ln(P₂/P₁) = -∆Hvap/R × (1/T₂ - 1/T₁)
Define molarity.
Mol solute / L of solution.
Why does H₂O have a higher BP than H₂S?
H₂O has hydrogen bonding, which is stronger than dipole-dipole forces in H₂S.
How does adding solute affect freezing point?
It decreases due to freezing point depression.
Which phase changes is endothermic?
List 3
Melting, vaporization, sublimation.
You dissolve 0.005 g of salt into 500 g of water. What is the concentration in ppm?
(0.005 g ÷ 500 g) × 10⁶ = 10 ppm
Define mass percent.
(mass solute / total mass solution) × 100
Which has higher vapor pressure: Br₂ or I₂?
Br₂—it has weaker dispersion forces due to smaller size.
Calculate the osmotic pressure of a solution containing 24.6 g of glycerin (C3H8O3) in 250.0 mL of solution at 298 K.
π = MRT (M = molarity, R = 0.0821, T in K).
Which will have the greater osmotic pressure: 1.0 M NaCl or 1.0 M glucose? Why?
NaCl, because it dissociates into 2 ions: i = 2.
You dissolve 2 moles of ethanol in 8 moles of water. What is the mole fraction of ethanol?
Mole fraction = 2 / (2 + 8) = 0.20
How to prep 4.67g CuCl₂ in 50 mL solution?
Use molar mass to find moles → M2 = mol / 0.050 L
Rank CH₄, CH₃CH₂Cl, CH₃CH₂OH by boiling point.
CH₄ < CH₃CH₂Cl < CH₃CH₂OH (strong hydrogen bonding in ethanol)
What is Raoult’s Law, and how does it explain vapor pressure lowering?
Vapor pressure of a solution is lower than that of a pure solvent because some surface molecules are solute and can’t escape. ΔP = X_solute × P°_solvent
How much heat to vaporize 25g of H₂O at 100°C?
q = m/18.015 × 40.7 = 56.5 kJ.
Which color of visible light has the highest frequency and energy: red, green, or violet?
Violet has the shortest wavelength and highest energy/frequency.
What is the energy of a photon with frequency 5.0 × 10¹⁴ Hz? (Use h = 6.63×10⁻³⁴ J·s)
E = hν = (6.63×10⁻³⁴)(5.0×10¹⁴)
3.32 × 10⁻¹⁹ J
Water vs. acetone—who has more surface tension & why?
Water—strong hydrogen bonding increases surface tension.
Calculate the freezing point of a solution containing 10.0 g of naphthalene (C10H8) in 100.0 mL of benzene. Benzene has a density of 0.877 g/cm3
Kf (benzene) = 5.12
mol C₁₀H₈=128.17 g/mol10.0 g≈0.0780 mol
mass of benzene=100.0 mL×0.877 g/mL=87.7 g=0.0877 kg
m=0.0877 kg0.0780 mol≈0.889 mol/kg
ΔTf=5.12 mol°C⋅kg×0.889 kgmol≈4.55 °C
Tsolution=5.5 °C−4.55 °C=0.95 °C
Methylamine has a vapor pressure of 344 torr at –25 °C and 760 torr at –6.4 °C.
Using this data, calculate the enthalpy of vaporization (∆Hvap) in kJ/mol.
23.426 kJ/mol
(Using ln(P₂/P₁) = ΔHvap/R × (1/T₁ – 1/T₂), plug in values and solve.)
A solution has 0.75 mol A (P° = 100 torr) and 0.25 mol B (P° = 50 torr). What is the vapor pressure lowering compared to pure A?
P_solution = (0.75)(100) + (0.25)(50) = 87.5
ΔP = 100 – 87.5 = 12.5 torr
A solution contains 15.0 g of glucose (C₆H₁₂O₆) dissolved in 200.0 g of water.
Calculate the freezing point of the solution. (Kf for water = 1.86 °C·kg/mol)
Molar mass glucose = 180.16 g/mol
Mol glucose = 15.0 ÷ 180.16 ≈ 0.0833 mol
Solvent in kg = 200.0 g = 0.200 kg
Molality = 0.0833 ÷ 0.200 = 0.417 m
ΔTf = 1.86 × 0.417 = 0.776 °C
Freezing point = 0 – 0.776 = –0.77 °C