Final Exam - Chem
The more volatile component in a solution is the one with the __________ vapor pressure.
greater
IV fluids must be __________ with body fluids.
isotonic
At a given temperature, the vapor pressure of the solvent in a solution containing nonvolatile solutes is __________ than the vapor pressure of the pure solvent.
less
The vapor pressure of a nonvolatile solution is __________ than the vapor pressure of the pure solvent.
lower
Reverse Osmosis
-Process in which the solvent is forced from high concentration of solutes to low concentration of solutes (against the concentration gradient) to separate the solvent and solute(s)
Van 't Hoff Factor (i factor) (define & equation)
-Ratio of the experimentally measured value of a colligative property to the theoretical value expected for that property if the solute were a nonelectrolyte - i = ΔTsubf / ( ksubf ⋅ m ) - i = ΔTsubb / ( ksubb ⋅ m )
Colligative Properties
Characteristics of solutions that depend only on the concentration of the solute particles (number of solute particles, NOT size), and NOT the identity of them
What process should you take when calculating the molar mass of water soluble substances?
Osmotic pressure
Explain what happens to the freezing point of sea water (salt water) in comparison to pure water.
Presence of sea salt ions prevents some water molecules from reaching the ice surface, reducing the number of freezing events, decreasing the freezing point (-2°C)
Under what conditions does a solution behave ideally?
When the strengths of the solvent-solvent, solute-solute, and solute-solvent interactions are similar
When do solutions such as the hydrocabons in crude oil obey Raoult's law?
When the strengths of the solvent-solvent, solute-solute, and solute-solvent interactions are similar
k constants are specific to the __________.
solvent
The van 't Hoff factor for an aqueous solution of an ionic compound is 2. Which of the following is / are NOT a possible explanation? a - The solute is a 1:1 salt behaving as an ideal solution b - The solute is a nonelectrolyte c - The solute is a 2:1 electrolyte behaving in a nonideal fashion d - The solute is a 1:1 salt of a weak electrolyte
b - The solute is a nonelectrolyte AND d - The solute is a 1:1 salt of a weak electrolyte
The presence of solutes __________ the range of temperatures at which the solution will remain a liquid.
expands / increases
Calculate the molality of 1 L of an aqueous solution of sodium chloride that is 0.558 M in NaCl at 25°C. The density of the solution is 1.022 g/mL.
- ( 1.022 mol NaCl / 1 L solution ) ( 1000 mL / 1 L ) = 1022 g solution - ( 0.558 mol NaCl / 1 L solution ) ( 58.44 g NaCl / 1 mol NaCl ) = 32.6 g NaCl / L solution - 1022 g solution - 32.6 g NaCl = 989 g solvent - molality = mol solute / kg solvent - molality = 0.558 mol / 0.989 kg solvent = molality = 0.564 m
The liquid used in automobile cooling systems is prepared by dissolving ethylene glycol (HOCH2CH2OH), molar mass 62.07 g/mol, in water. What is the vapor pressure of a solution prepared by mixing 1.000 L of ethylene glycol (density 1.114 g/mL) with 1.000 L of water (density 1.000 g/mL) at 100.0°C?
- 1000 mL ( 1.114 g / 1 mL ) ( 1 mol / 62.07 g ) = 17. 95 mol ethylene glycol - 1000 mL ( 1.000 g / 1 mL ) ( 1 mol / 18.02 g ) = 55.49 mol H2O - The number of moles of water is more than the moles of ethylene glycol, so water is the solvent - Xwater = 55.49 mol / ( 55.49 mol + 17.95 mol ) = Xwater = 0.7556 - Psolution = ( Xsolvent ) ( P°solvent ) - Psolution = ( 0.7556 ) ( 1.00 atm ) = Psolution = 0.756 atm
Red blood cells placed in seawater shrivel. Calculate the pressure across the semipermeable cell membrane separating the solution inside a red blood cell from seawater at 25°C if the total concentration of the particles inside the cell is 0.30 M and the total concentration of ions in seawater is 1.15 M.
- 25°C + 273 = 298 K - II = ( iMseawater - iMrbc ) RT - II = ( 1.15 M - 0.30 M ) ( 0.08206 L⋅atm/mol⋅K ) ( 298 K ) = II = 21 atm
The concentration of solutes in a red blood cell is about a third of that seawater--more precisely, about 0.30 M. If red blood cells are immersed in pure water, they swell. Calculate the osmotic pressure at 25°C of red blood cells across the cell membrane from pure water.
- 25°C + 273 = 298 K - II = iMRT - II = ( 0.30 M ) ( 0.08206 L⋅atm/mol⋅K ) ( 298 K ) = II = 7.3 atm
How many grams of Na2SO4 should be added to 275 mL of water to prepare a 0.750 m solution of Na2SO4? Assume the density of water is 1.000 g/mL.
- 275 mL ( 1.000 g / mL ) ( kg / 1000 g ) = 0.275 kg H2O - m = mol solute / kg solvent - 0.750 m = x / 0.275 kg - x = 0.20625 mol Na2SO4 - 0.20625 mol ( 142.05 g / mol ) = 29.3 g Na2SO4
Ethanol, CH3CH2OH, is used to disinfect the skin prior to getting a shot. The solution quickly evaporates at 37°C, roughly the body temperature of a healthy human. Calculate the vapor pressure of a solution prepared by dissolving 5.0 g of water in 78.0 g of ethanol at 37°C. By what factor does the concentration of the more volatile component in the vapor exceed the concentration of this component in the liquid? The vapor pressures of ethanol and water at 37°C are 115 torr and 47 torr, respectively.
- 78.0 g CH3CH2OH ( 1 mol / 6.068 g ) = 1.69 mol ethanol - 5.0 g H2O ( 1 mol / 18.016 g ) = 0.28 mol H2O - 1.69 mol + 0.28 mol = 1.97 mol - Xethanol = 1.69 mol / 1.97 mol = Xethanol = 0.858 - Xwater = 1 - 0.858 - Xwater = 0.142 - Psolution = ( Xwater ) ( P°water ) + ( Xethanol ) ( P°ethanol ) - ( 0.142 ) ( 47 torr ) + ( 0.858 ) ( 115 torr ) = 6.7 torr + 98.7 torr = Psolution = 105.5 torr - 98.7 torr / 6.7 torr = 14.7 (ratio of vapor pressures) - 1.69 mol / 0.28 mol = 6.0 (ratio of ethanol to water - 14.7 / 6.0 = 2.5 ANSWER: - Psolution = 105.5 torr - Vapor pressure is enriched in ethanol by a factor of 2.4
What is the reverse osmotic pressure required at 20°C to purify brackish well water containing 0.355 M dissolved particles if the purified water is to contain no more than 87 mg of dissolved solids (measured as NaCl equivalents) per liter?
- 87 mg / L ( g / 1000 mg ) ( mol / 58.44 g ) = 1.5 x 10^3 M NaCl - II = ( iMbrackishwater - iMdrinkablewater ) RT - II = ( 0.355 M - ( 2 ⋅ 1.5x10^-3 M ) ) ( 0.08206 L⋅atm/mol⋅K ) ( 293 K ) - II = 8.47 atm
A molecular compound that is a noneletrolyte was isolated from a South African tree. A 47 mg sample was dissolved in water to make 2.50 mL of solution at 25°C, and the osmotic pressure of the solution was 0.489 atm. Calculate the molar mass of the compound.
- II = iMRT - 0.489 atm = ( 1 ) ( M ) ( 0.08206 L⋅atm/mol⋅K ) ( 298 K ) = M = 0.0200 M - n = M / V - n = ( 0.0200 mol / L ) ( 0.00250 L ) = n = 5.00 x 10^-5 mol - molar mass = g/mol - molar mass = ( 0.047 g ) / ( 5.00 x 10^-5 mol ) = molar mass = 9.4 x 10^2 g/mol
The salt lithium perchlorate (LiClO4) is one of the most water-soluble salts known. At what temperature does a 0.130 m solution of LiClO4 freeze? The kubf of water is 1.86°C/m.
- i = ΔT / ( ksubf ⋅ m ) - 2 = ΔT / ( 1.86 °C/m ) ( 0.130 m ) - ΔT = 0.483°C decrease - 0°C - 0.483°C = -0.483°C
The experimentally measured freezing point of a 1.90 m aqueous solution of NaCl is -6.57°C. What is the value of the van 't Hoff factor for this solution? Is the solution behaving ideally, or is there evidence that solute particles are interacting with one another? The freezing point depression constant of water is ksubf = 1.86°C/m, and the freezing point of pure water is 0.00°C.
- i = ΔT / ( ksubf ⋅ m ) - i = 6.57°C / ( 1.86°C/m ⋅ 1.90 m ) = i = 1.86
Osmotic pressure directly balances the __________ ( __________ ) that is driving solvent through the membrane so that no net flow of solvent takes place.
- pressure - F/A P = F / A - P = pressure - F = force - A = surface area
The extent to which free ions form when a strong electrolyte dissolves is expressed by the __________. Whenever a calculation for i gives a noninteger value, the solute particles are __________ in the solution, and the behavior is __________.
- van 't Hoff factor -associating -nonideal
Boiling Point Elevation Equation
- ΔTb = increase in temperature above the boiling point of the pure solvent - ksubb = boiling point elevation constant of the solvent (°C/m) - m = molality of the solution
Hospital use a 0.159 m NaCl solution or a 0.304 m glucose solution to deliver medications intravenously. What are the boiling points of these solutions?
- ΔTb = ksubb ⋅ m - For NaCl, m = 0.159 m, but since NaCl dissolves in water, it produces 2 moles of products (Na+ and Cl-), so m of NaCl = vv - m NaCl = ( 0.159 m ) ( 2 ) = m NaCl = 0.318 m - ΔTb NaCl = ( 0.52°C/m ) ( 0.318 m ) = ΔTb NaCl = 0.17°C increase - 0.17°C + 100°C = 100.17°C NaCl - For glucose, m = 0.304 m, as the problem states, because glucose does not dissociate into ions in water - ΔTb glucose = ( 0.52°C/m ) ( 0.304 m ) = ΔTb glucose = 0.16°C increase - 0.16°C + 100°C = 100.16°C glucose
Freezing Point Depression Equation
- ΔTf = increase in decrease below the boiling point of the pure solvent - ksubf = freezing point depression constant of the solvent (°C/m) - m = molality of the solution
What is the freezing point of radiator fluid prepared by mixing 1.00 L of ethylene glycol (HOCH2CH2OH, density 1.114 g/mL) with 1.00 L of water (density 1.000 g/mL)? The freezing point depressing constant is 1.86°C/m.
- ΔTf = ksubf ⋅ m - 1.00 L HOCH2CH2OH ( 1000 mL / L ) ( 1.114 g / mL ) ( mol / 62.068 g ) = 17.9 mol HOCH2CH2OH - 1.00 L H2O ( 1000 mL / L ) ( 1.000 g / mL ) ( kg / 1000 K ) = 1.00 kg H2O - m = mol solute / kg solution - m = 17.9 mol / 1.00 kg H2O = m = 17.9 m - ΔTf = ( 1.86°C/m ) ( 17.9 mol/kg ) = ΔTf = 33.3°C decrease - 0°C - 33.3°C = -33.3°C
Eicosene is a molecular compound and nonelectrolyte with the empirical formula of CH2. The freezing point of a solution prepared by dissolving 100 mg of eicosene in 1.00 g of benzene was 1.75° lower than the freezing point of pure benzene. What is the molar mass of eicosene? Ksubf for benezene equals 4.90°C/m.
- ΔTsubf = ksubf ⋅ m - 1.75°C = ( 4.90°C/m ) ( m eicosene ) = m eicosene = 0.357 m - 1.00 g benzene = 0.001 kg benzene - mol eicosene = ( 0.375 mol eicosene / 1 kg benzene ) ( 0.001 kg benzene ) = mol eicosene = 3.57 x 10^-4 mol - molar mass = g/mol - 100 mg eicosene used ==> 0.100 g eicosene used - ( 0.100 g ) / ( 3.57 x 10^-4 mol ) = molar mass eicosene = 280. g/mol
How can we determine the molar mass of nonelectrolytes??
-Dissolve a known quantity of the solute into a known quantity of solvent -Measure the effect that the dissolved solute has on any colligative property of the solvent
When reading a heating curve, how can you tell the composition of a solution at a certain temperature?
-Go to the temperature you want (on the blue line) -Move left to the red line, and follow that down to the x-axis for the composition
Hypertonic
-Having a higher concentration of solute than another solution -Cell shrivels because water leaves the cell
Hypotonic
-Having a lower concentration of solute than another solution -Cell swells up because water enters the cell
What are the units on molarity? Molality?
-Molarity: mol solute / L solution -Molality: mol solute / kg solvent
What does i equal if the solute is molecular / a nonelectrolye? What does i equal if the solute is a strong electrolyte?
-Molecular / Nonelectrolyte: 1 (because each more of solute produces 1 mole of dissolved particles) -Strong Electrolyte: Number of ions in one formula unit (ex: for NaCl, i = 2, for Na2SO4, i = 3, etc)
Osmosis
-The flow of a fluid through a selectively permeable membrane to balance the concentration of solutes in solutions on the 2 sides of the membrane -The solvent particles flow proceeds from the more dilute solution into the more concentrated one
What happens when adjoining a compartment of pure water with a compartment of seawater?
-Volume of pure water decreases at the same rate as the volume of seawater increases, resulting in nearly all of the water in the seawater compartment -Water in both compartments evaporates -Concentration of water vapor in the air space of the sealed chamber increases, which, in turn, increases the pressure that the water vapor exerts on the 2 liquid surfaces -At this point, the rate of evaporization then equals the rate of condensation -Then, rates of condensation are the same, but the rates of evaporization are not (pure water has a higher rate of evaporization than seawater) -More water vapor enters the air in the chamber from the pure water compartment than from the seawater compartment because the vapor pressure of the pure water is greater than the vapor pressure of the seawater
The lower the vapor pressure of a solution in relation to the vapor pressure of pure solvent depends only on the ___________, not their __________.
-concentration of solute particles -identity
When using fractional distillation for a pure substance, it makes the phase change from liquid to vapor at a(n) __________ temperature. When using fractional distillation of a solution of 2 volatile substances, it makes the phase change from liquid to vapor at a(n) __________ temperature.
-constant -not constant (temperature increases)
Solutions generally have __________ densities than the solvent alone, and an aqueous solution containing a nonvolatile solute has a(n) __________ boiling point and a(n) __________ freezing point than pure water. Both ___________ and __________ are colligative properties.
-greater -higher -lower -elevated boiling point -depressed freezing point
When calculating the freezing point depressions and boiling point elevations for concentrated solutions of strong electrolytes, they often give __________ values than the experimentally measured values. The reason is that the cations and anions produced when strong electrolytes dissolve may not be totally __________ of each other. As concentration increases, cations and ions may form __________. The simplest cluster is a(n) __________.
-larger -independent -ion cluster -ion pair
For all aqueous solution, __________ is greater than __________.
-molality -molarity
For fractional distillation, in the vapor in equilibrium with a solution of 2 volatile substances, the concentration of the lower boiling (__________ volatile) component is always __________ in the vapor than in the liquid.
-more -greater
On a heating curve for fractional distillation, the __________ line is tells the composition of the vapor above the solution at a given temperature, and the __________ line tells the temperature of the boiling solution.
-red -blue
A solution and pure solvent are separated by a semipermeable membrane. The __________ molecules can pass through the membrane, but the __________ particles cannot. Solvent will flow in order to try and equalize concentrations. Thus, solvent flows into the __________. This is called osmosis. Eventually, a pressure difference between solvent and solution will build up to prevent further net exchange. This is called the __________. Another way to view osmotic pressure is that is is the pressure required to __________ osmosis.
-solvent -solute -solution -osmosis -osmotic pressure -stop
If the solute-solvent interactions are __________ than the solvent-solvent or solute-solute interactions, the solute inhibits the solvent from vaporizing, and the solvent inhibits the solute from vaporizing. This situation produces __________ deviations from the vapor pressures predicted by Raoult's law. In such a solution, the rate of evaporation is __________ because the vapor pressure of the mixture is __________ than predicted. Because the solvent and solute molecules are held at the surface of the solute-solvent attractive interactions, __________ energy is required to separate them from the surface, and __________ vaporize at a given temperature. If solute-solvent interactions are much __________ than the solvent-solvent interactions, less energy is required to separate the solute molecules from the surface, and __________ solute molecules vaporize. In this case, the vapor pressure is __________ than the value predicted by Raoult's law.
-stronger -negative -slower -lower -more -fewer -weaker -more -greater
What is the boiling point elevation constant (ksubb) of water, and what is the contextual meaning?
0.52°C/m aka for every mole of particles that dissolves in 1 kg of water, the boiling point of the solution rises by 0.52°C
All mole fractions must add up to ___.
1
What would a heating curve look like for the fractional distillation of . . . 1) 75 mL octane and 25 mL heptane? 2) 75 mL octane and 25 mL nonane? The normal boiling points of heptane, octane, and nonane are 98°C, 126°C, and 151°C, respectively.
75 ML OCTANE & 25 ML HEPTANE: -The first component that distills is heptane because it has a lower boiling point -25 mL of heptane would distill at 98°C -When the heptane was removed from the solution, the only remaining component (75 mL octane) would distill at 126°C 75 ML OCTANE & 25 ML NONANE: -The first component that distills is octane because it has a lower boiling point -75 mL of octane would distill at 126°C -When the octane was removed from the solution, the only remaining component (25 mL nonane) would distill at 151°C
Ion Pair
A cluster formed when a cation and anion associate with each other in a solution, acting as a single particle
Raoult's Law Equation
Applies to nonvolatile solutes on the boiling point of a pure solvent, and applies to homogeneous mixtures of volatile compounds
Why is a mixture of hydrocarbons expected to behave like an ideal solution?
Because intermolecular interactions between the components are all London forces acting on molecules of similar structure and size
Molality (m)
Concentration expressed as moles of solute per kg of solvent
Isotonic
Concentration of 2 solutions is the same
Nonvolatile
Doesn't vaporize easily
T or F A concentration expressed in molality changes with temperature.
False - Because solvent mass does not change with temperature, a concentration expressed in molality does not change with temperature
What is the equation for the difference in osmotic pressures between 2 solutions of different concentrations?
II = (iMsolution1 - iMsolution2)RT
How does the value of Ksubb change if units K were used instead of Celsius?
It stays the same
How are colligative properties related to concentration?
Lineraly
Higher Boiling Point = __________ Vapor Pressure
Lower
Fractional Distillation
Method of separating volatile components of a mixture on the basis that they have different boiling points
The temperature in the sealed container of pure water and sea water compartments is 20°C. The vapor pressure of pure water at this temperature is 0.0231 atm. What is the vapor pressure produced by the evaporation of water from seawater if the mole fraction of water in the sample is 0.980?
Psolution = ( Xsolvent ) ( P°solvent ) Psolution = ( 0.980 ) ( 0.0231 atm ) = Psolution = 0.0226 atm
What is the equation for the total vapor pressure of a solution containing volatile solutes?
Ptotal = X1P°1 + X2P°2 + X3P°3 + etc.
What is the slope of the osmotic pressure equation?
RT
Ideal Solution
Solution that obeys Raoult's law
Osmotic Pressure (II) (define & equation)
The pressure required to halt the flow of solvent from a solution through a semipermeable membrane into pure solvent - i = van 't Hoff factor - M = solute molarity - R - 0.08206 L⋅atm/mol⋅K - T = solution temperature
T or F Solute does not contribute to the vapor pressure with nonvolatile substances.
True
The presence of a nonvolatile solute causes vapor pressure to __________.
decrease
Colligative properties are properties of solutions that change when the __________ changes.
concentration
Because the vapor pressure of seawater at 20°C is slightly lower than the vapor pressure of pure water at 20°C, seawater __________ more slowly than pure water.
evaporates
A solution which obeys Raoult's law is called a(n) __________.
ideal solution
The extent of ion pairing in a solution of a strong electrolyte generally __________ with solute concentration as the solution runs out of water needed to form spheres of hydration around the ions.
increases
In ideal solutions, the solute and solvent experience similar __________.
intermolecular forces
