Chemistry 112 Chapter 13
Calculate the freezing point of a solution containing 0.204 mol of ibuprofen in 250. g of ethanol. (Kf for ethanol = 1.99oC⋅kg/mol and Tf = -117.3oC.)
-118.9oC Reason: ΔTf = 0.204/0.250 × 1.99 = 1.62oC and Tf = -117.3oC - 1.62oC = -118.9oC
What is the solubility of argon in water at 25∘C if the partial pressure of argon in air is 0.00916 atm? Henry's law constant for argon is1.61 mol/L·atm.
0.0147 mol/L
A solution of 1.80 g of a nonelectrolyte in 500.0 mL of water at 27.0°C has an osmotic pressure of 39.5 mmHg. What is the molar mass of the compound?
1.71 × 103 g/mol Reason: M = ΠRT = 39.5mmHg/760mmHg/1atm(0.0821atm⋅Lmol⋅K)(273.15K+27.0°C) = 2.11 × 10-3 M Moles of solute = M × V = 2.11 × 10-3 M × 0.500 L = 1.05 × 10-3 mol molar mass = 1.80g/1.05×10−3mol = 1.71 × 103 g/mol
A 0.50% by mass solution of KCl (molar mass 74.55 g/mol) in H2O (Kf = 1.86oC/m) has a freezing point of -0.234oC. What is the van't Hoff factor i for this solution?
1.87 Reason: The molality is 6.71×10−3mol0.0995kg = 0.0674 m since there are 0.50 g in 99.50 g of H2O, not 0.50 g in 100.00 g of H2O. i = ΔTfKfm = 0.234°C1.86°C/m×0.0674m = 1.87
Calculate the expected boiling point of a solution containing 0.72 mol of MgCl2 in 1.00 kg of H2O if Kb = 0.512°C⋅kg/mol. Multiple choice question.
100.0°C + (2.16 × 0.512) = 101.1oC Reason: MgCl2 dissociates to form three ions, so i = 3 and the molality is 2.16 mol/kg.
A solution contains 25.0 g ethanol (C2H5OH; molar mass 46.07 g/mol) in 500. g H2O (molar mass 18.02 g/mol) at 23oC. If the vapor pressure of pure H2O at this temperature is 20.57 torr, What is the vapor pressure of the solution?
20.1 torr Reason: Psoln = χsolvent x P°solvent. Since H2O is the solvent, we use χwater for this calculation. χwater = 27.728.3 = 0.979 Psoln = 0.979 x 20.57 = 20.1 torr
Which of the following statements correctly describe the structure and behavior of colloids? Select all that apply.
A colloid in H2O is stabilized by ion-dipole forces between the charged surfaces of the colloid particles and the H2O molecules. There are different types of colloids, classified by the physical state of their components. Colloid particles will coagulate and settle from the dispersion if the colloid is heated.
Certain substances such as alcohols are able to dissolve fairly readily in both polar and nonpolar solvents. Which statements correctly explain this behavior? Select all that apply. Multiple select question.
Alcohols form strong interactions with both types of solvent. Alcohols have dual polarity since they possess a polar OH group as well as a nonpolar hydrocarbon portion. The hydrocarbon portion of the alcohol interacts with the nonpolar solvent through dispersion forces.
Which of the following statements correctly relate the charge density of an ion to heat of hydration? Select all that apply.
As the charge on an ion increases and its radius decreases, its charge density will increase and so will the magnitude of the heat of hydration. An ion with a higher charge density has a more negative heat of hydration than an ion of similar size but lower charge.
Which of the following options correctly reflect the effect of a nonvolatile solute on the boiling point of a solution? Select all that apply.
Boiling point elevation occurs because the presence of a nonvolatile solute lowers the vapor pressure of the solvent. A solution boils at a higher temperature than the pure solvent. The lower the concentration of the nonvolatile solute, the higher the vapor pressure of the solution. The greater the concentration of the solute, the higher the boiling point will be.
A solution containing 0.64 g of adrenaline in 36.0 g of CCl4 has a boiling point of 76.99°C (Kb for CCl4 = 5.03°C/m and its normal boiling point is 76.50°C). Place the following steps in the correct order to calculate the molar mass of adrenaline, starting with the first step at the top of the list.
C m moles of adrenaline g/mol
Which of the following statements correctly describe freezing point depression for a solution? Select all that apply. Multiple select question.
Freezing point depression is proportional to the molality of the solution. The freezing point constant Kf is characteristic of the solvent. ΔTf is a positive value.
Will HCl (g) or NaCl (s) be more soluble in the solvent CH3OCH3? Why?
HCl (g) will be more soluble in CH3OCH3. The dipole-dipole forces in an HCl solution are similar in strength to the dipole-dipole forces between CH3OCH3 molecules.
Which of the following statements correctly describe the osmotic pressure (Π) of a solution? Select all that apply.
Osmotic pressure is directly proportional to the molarity of the solution. Osmotic pressure increases with temperature.
Which of the following statements correctly explain the effect of a nonvolatile solute on the vapor pressure of a solution? Select all that apply.
Solute particles on the solution surface decrease the number of solvent particles that can escape. Vapor pressure is lowered. The entropy of the solution is higher than that of the pure solvent. Solvent has less tendency to vaporize, and the vapor pressure is lowered.
Match each different type of mixture to the correct description.
Suspension matches Choice, A heterogeneous mixture containing particles large enough to be seen by the naked eye; particles will settle out on standing A heterogeneous mixture containing particles large enough to be seen by the naked eye; particles will settle out on standing Solution matches Choice, A homogeneous mixture where the particles are too small to be visible; particles are distributed evenly in the solvent A homogeneous mixture where the particles are too small to be visible; particles are distributed evenly in the solvent Colloid matches Choice, A dispersion of particles in a dispersing medium; particles are too small to settle out but large enough to scatter light A dispersion of particles in a dispersing medium; particles are too small to settle out but large enough to scatter light
Which of the following options correctly describe a solution that is in contact with undissolved solute at a given temperature? Select all that apply.
The concentration of dissolved solute will not change. The rate at which solute is dissolving is equal to the rate at which solute particles are crystallizing from solution. Undissolved solute is in equilibrium with dissolved solute.
Which of the following statements correctly describe the vapor pressure of a solution containing a volatile nonelectrolyte solute? Select all that apply.
The fraction of the volatile component in the vapor will be greater than that in the solution. The vapor pressures of both volatile components will be lowered. The vapor pressure of each volatile component can still be calculated using PA = XAPoA.
Which of the following statements correctly describe the enthalpy changes associated with the formation of a solution? Select all that apply.
The overall enthalpy change for the solution process depends on the balance of energy absorbed vs. energy released. Energy is released when the solvent and solute particles attract each other and mix to form a solution. Energy is absorbed to separate the solvent particles from each other.
Which of the following options that correctly describe Henry's law for gases? Select all that apply. Sgas = kH x Pgas
This law shows that the solubility of a gas increases with pressure. Sgas is the solubility of the gas at a particular temperature. Pgas is the partial pressure of the gas above the liquid.
In a liquid solution containing two or more volatile components, the mole fraction of the most volatile component will be -----------than that of any other component(s) in the vapor above the solution.
higher
A solution is made by dissolving 67.7 g of urea (CH4N2O; molar mass = 60.06 g/mol) in 833 g of CHCl3 (molar mass = 119.36 g/mol). Order the following steps correctly to calculate the boiling point of the solution if Kb for CHCl3 = 3.85°C⋅kg/mol and the normal boiling point for this solvent is 61.2°C. Place the first step at the top.
mol mol/kg Delta Tb Tb
Which of the following statements correctly describe the heat of solvation, ΔHsolvation, and heat of hydration, ΔHhydr, for a solution process? Select all that apply
ΔHsoln = ΔHsolute + ΔHsolvation ΔHsolvation = ΔHsolvent + ΔHmix
A solution contains 0.32 mol naphthalene in 5.50 mol of toluene at 32oC. Pure toluene has a vapor pressure of 41 torr at this temperature. Which of the following options correctly solve for both P and ΔP for this solution? Select all that apply.
ΔP = 0.32/0.32+5.50 x 41 = 2.3 torr P = 5.50/0.32+5.50 x 41 = 39 torr
Which of the following options correctly show the relationships between solute concentration and solution vapor pressure? Select all that apply.
ΔP = Xsolute x P°solvent Psolvent = Xsolvent x P°solvent
Click and drag on elements in order Place the following aqueous solutions in increasing order (lowest at the top of the list) of osmotic pressure, assuming ideal behavior.
Correct Answer 0.15 M glucose (C6H12O6) 0.10 M KBr 0.10 M Fe(NO3)3 0.15 M CuCl2
What mass of pyrazole (C3H4N2; molar mass = 68.08 g/mol) must be added to 451 g of benzene (C6H6; molar mass = 78.11 g/mol) in order for the solution to have a freezing point of 0.5oC? (Kf for benzene = 5.12oC ⋅ kg/mol and the normal freezing point for this solvent is 5.5oC). Order the steps required to solve this problem correctly. Start with the first step at the top of the list.
Delta Tf m mole gram
A solution containing benzoic acid (C6H5COOH; molar mass = 122.12 g/mol) in 78.1 g of ethanol (C2H5OH; molar mass = 46.07 g/mol) boils at a temperature of 82.5°C. Kb for ethanol is 1.20°C⋅kg/mol, and the normal boiling point for this solvent is 78.1°C. Match the appropriate calculation with each variable needed to solve for the mass of benzoic acid.
ΔTb = matches Choice, 82.5°C - 78.1°C 82.5°C - 78.1°C m = matches Choice, 4.4°C1.20°C⋅kg/mol 4.4°C1.20°C⋅kg/mol Moles of benzoic acid present = matches Choice, 78.1 g ethanol ×1kg1000g×3.7molbenzoicacid1kgethanol 78.1 g ethanol × 1kg1000g × 3.7mol benzoic acid1kg ethanol Mass of benzoic acid = matches Choice, 0.29 mol ×122.12g1mol 0.29 mol × 122.12g1mol
