IMF's
Which intermolecular force is responsible for water’s unusually high boiling point?
What is Hydrogen Bonding?
During melting, does temperature change? What happens to the added energy?
No. The added energy is used to break the intermolecular forces, not to increase kinetic energy of the particles within the atom.
What generally happens to the solubility of a solid in water as temperature increases?
Solubility Increases
Calculate the molarity of a solution made by dissolving 5.00 g NaCl in 250 mL of solution.
(MM NaCl = 58.45 g/mol)
.342M
Name two properties that depend only on the number of solute particles, not their identity.
Boiling point elevation and freezing point depression.
Adding solute increases boiling point or decreases freezing point.
Rank the following in order of increasing IMF strength:
London dispersion, hydrogen bonding, dipole–dipole, ion-dipole.
London dispersion forces < dipole-dipole interactions < hydrogen bonds < ion-dipole
How much energy is required to melt 25.0 g of ice at 0 °C?
(Given ΔH₍fus₎ = 6.02 kJ/mol)
(Given ΔH₍vap₎ = 40.7 kJ/mol)
(Given MM H2O = 18.0 g/mol)
8.36kJ or 8,361.1J
Why does the solubility of gases in water decrease as temperature increases?
As temperature increases, gases become less soluble in water because dissolution is exothermic and added heat drives gas molecules out of solution.
How many grams of CaCl₂ are needed to prepare 500 mL of 0.200 M solution?
(MM CaCl2 = 110.9)
11.09g
Why does NaCl have a larger effect on boiling point elevation than glucose at the same concentration?
Two compounds have similar molar masses, but one boils much higher. What IMF difference could explain this?
What is hydrogen bonding?
Calculate the energy needed to vaporize 75.0 g of water at 100 °C.
(ΔH₍vap₎ = 40.7 kJ/mol)
(ΔH₍fus₎ = 6.02 kJ/mol)
(MM H2O = 18.0 g/mol)
169.6kJ
Which salt is more soluble in water: NaCl or AgCl? Explain using intermolecular interactions.
NaCl is more soluble in water because its ions are more easily stabilized by ion–dipole interactions with water, whereas the strong ion–ion attractions in AgCl make it much less soluble.
You dissolve 10.0 g NaOH in water to make 500 mL solution. Calculate:
a) Molarity
b) Molality (assume density of solution ≈ 1.05 g/mL)
c) Mole fraction of NaOH
Given:
MM NaOH = 40 g/mol
Molarity: 0.5
Molality: 0.485
Mole Fraction: .0087
A solution is prepared by dissolving 10.0 g of a nonvolatile solute in 150 g of water. The freezing point of the solution is found to be –0.93 °C. Calculate the molality of the solution. (Kf for water =1.86 °C·kg/mol)
m=0.5
Between CH₃OH and CH₃SH, which has stronger IMFs and why?
what is CH₃OH?
Calculate the total energy required to heat 10.0 g of ice at −10 °C to steam at 100 °C. Answer in kJ.
(ΔH₍vap₎ = 40.7 kJ/mol) CsH2O = 4.184 J/goC
(ΔH₍fus₎ = 6.02 kJ/mol)
(MM H2O = 18.0 g/mol)
30.6kJ
A solubility curve shows that KNO₃ solubility increases sharply with temperature. What does this imply about its dissolution process?
A sharp increase in KNO₃ solubility with temperature indicates that its dissolution is endothermic, so added heat increases solubility.
A chemist prepares a solution by dissolving 25.0 g glucose in 150 g of water. Calculate:
a) Molality
b) Molarity (assume solution volume = 175 mL)
c) Mole fraction of glucose
MM of glucose = 180.156 g/mol
MM of water = 18.0 g/mol
Molality: 0.925
Molarity: 0.793
Mole Fraction of glucose: .016
A 0.250 g sample of a protein is dissolved in 125 mL of water. The solution exerts an osmotic pressure of 3.15 atm at 25 °C. Calculate the molar mass of the protein. (R = 0.08206 L·atm/mol·K)
MM = 15.5 g/mol
Explain why iodine (I₂) is a solid at room temperature while chlorine (Cl₂) is a gas, even though both are nonpolar.
Iodine is solid at room temperature because it's a larger atom causing more polarization in its electron cloud which leads to stronger London Dispersion forces causing it to have a higher melting and boiling point.
A heating curve shows a long flat region at the boiling point. What does this indicate, and how would you calculate the energy absorbed during this region?
This accounts for the breaking of IMF's and the occurring of a phase change. You would use Q=nΔH to calculate for this.
Explain why CO₂ is more soluble in cold soda than warm soda, and how this relates to pressure and temperature.
CO₂ is more soluble in cold soda because gas solubility increases at lower temperatures and higher pressures. Warming or lowering pressure allows CO₂ to escape from solution.
A solution contains 46.0 g ethanol and 36.0 g NaCl in 100 g water. Calculate:
a) Molality of each solute
b) Mole fraction of each solute
MM ethanol: 46.069 g/mol
MM NaCl: 58.45 g/mol
MM water: 18.0 g/mol
A: Ethanol: 9.99m NaCl: 6.16m
B: Ethanol: 0.139 NaCl: 0.086
You want to raise the boiling point of 250 g of water by 0.85 °C. You plan to dissolve an electrolyte solute that dissociates completely into 2 ions. The boiling point elevation constant is Kb=0.512 °C·kg/mol. If the solute has a molar mass of 74 g/mol, how many grams of solute are needed?
m = 15.4g