reading guide 4
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CHEM1212Spring2021Module4.docxName: __________ KEY_________________________
CHEM 1212 Module 4 Reading Guide
Solutions
Solutions are ____________ mixtures of two or more substances. The component present in larger quantity is usually identified as the ____________, and the material that is mixed into the solvent is called the ____________. Substances dissolve in one another if the solute and solvent are able to form ____________ attractions. When the strengths of the intermolecular forces of attraction between solute and solvent species in a solution are ____________ those present in the separated components, the solution is formed with no accompanying energy change. Such a solution is called an ____________.
Two considerations that favor, but do not guarantee, the spontaneous formation of a solution are:
1. A decrease in the internal energy. A release of energy to the surroundings is ____________, and results in a final state that is more ____________.
2. An increased dispersal of matter, and thus energy throughout the system. This is described as ____________, a measure of a system’s disorder or dispersal of particles throughout a system.
Enthalpy changes (ΔH) in the formation of most solutions involve differences in attractive forces between the solute and solvent particles. ____________ (or hydration for water) is the process of forming solute to solvent attractions.
In order for the solvent and solute to mix, the system must overcome:
1. solute–solute interactions [ (ΔHsolute), ____thermic process] To dissolve an ionic compound, an amount of energy equal to the ____________ energy must be added to the system.
2. solvent–solvent interactions [ (ΔHsolvent), ____thermic process]
At least some of the energy to do this comes from making new solute–solvent interactions during solvation [(ΔHsolution), ____thermic]. The relative magnitudes of the energy changes associated with these stepwise processes determine whether the dissolution process overall will release or absorb energy.
If the energy released in the solvation step is ____________ than the sum of the energies absorbed to disrupt the pure substances, the overall enthalpy of solution, ∆Hsol, will be ____________. If the energy released in the solvation step is ____________ than the sum of the two endothermic steps, however, then the enthalpy of solution will be ____________. If the solute’s electrostatic forces are significantly greater than the ____________ forces, the dissolution process is significantly endothermic and the compound may not dissolve to an appreciable extent.
Practice Problems
7. Which substance would you expect to be more soluble in water: chloroform, CHCl3, or carbon tetrachloride, CCl4? Which would you expect to be more soluble in C6H6? Explain your reasoning.
Solubility
Most gaseous and solid solutes will dissolve only to a certain extent in a given liquid solvent at a given ____________. The ____________ of a solute in a particular solvent is the ____________ concentration that may be achieved under given conditions when the dissolution process is at ____________. Solute solubility is a dynamic equilibrium process between ____________ and recrystallizing. Solubility is generally given in grams of solute that will dissolve per 100 grams of solvent.
When a solute’s concentration is equal to its solubility, the solution is said to be ____________ with that solute. If the solution contains less than the ____________ amount of solute, the solution is said to be ____________. The easiest way to tell that a solution is saturated is if excess solute is present that will not dissolve. A solution that contains a relatively low concentration of solute is called ____________, and one with a relatively high concentration is called concentrated. a situation in which more solute is dissolved in the solvent than is stable at that temperature is said to be ____________, a nonequilibrium state.
A change in temperature affects the solubility of a solute in a given solvent. Most solid solutes become ____________ soluble in liquid solvents as the temperature ____________.
Gas molecules have greater ____________ energy and are more easily able to escape the liquid into the gas phase. At any given temperature, the solubility of a gas in a liquid is directly proportional to the ____________ of the gas above the ____________ of the liquid.
Henry’s law: The quantity of an ideal gas that dissolves in a definite volume of liquid is directly proportional to the pressure of the gas.
C=kP
where k is the ____________, which depends on temperature and is different for each combination of gas and solvent, and P is the partial pressure.
Deviations from Henry’s law are observed when a ____________ takes place between the gaseous solute and the solvent.
Terms like saturated are normally reserved for a solid or a gas dissolved in a liquid and do not apply to solutions that are made up solutes and solvents in the ____________ phase, because there is no upper limit to the solubility in these cases. Some liquids may be mixed in ____________ proportions to yield solutions; in other words, they have infinite mutual solubility and are said to be ____________. They usually have the ____________ type of intermolecular forces between their molecules. When two liquids have ____________ intermolecular forces between their particles and ____________ mix to an appreciable extent, they are called immiscible.
Practice Problems
12. A 15.00 g sample of a solid substance is placed in 100.0 g of water at 25°C, and all of the solid dissolves. Then another 2.00 g of the substance is added, and all of it dissolves. A final 2.00 g is added, and none of it dissolves.
a. Is the first solution saturated, unsaturated, or supersaturated?
b. Is the second solution saturated, unsaturated, or supersaturated?
c. What can you tell about the final solution that is in contact with the solid?
Electrolytes
When some substances are dissolved in water, they undergo either a ____________ or a chemical change that yields ions in solution. These substances are called ____________. Substances that do not yield ions when dissolved are called ____________. If the physical or chemical process that generates the ions is essentially 100% efficient (all of the dissolved compound yields ions), then the substance is known as a ____________. If only a relatively small fraction of the dissolved substance undergoes the ion-producing process, it is called a ____________ .
The electrostatic attraction between an ____________ and a molecule with a ____________ is called an ion-dipole attraction. These attractions play an important role in the dissolution of ionic compounds in water.
In some cases, solutions prepared from covalent compounds conduct electricity because the solute molecules react chemically with the solvent to produce ____________.
An experimentally measured parameter is the ____________ (i ), defined as the ratio of solute particles in solution to the number of formula units dissolved.
The theoretical value is determined by counting the ____________ of ions the compound dissociates into. At high concentration or with larger ion charges, you still experience some interaction between the ions instead of them being completely separated and shielded from each other by the solvent molecules. The formation of these ____________ causes measured van’t Hoff factors to often be ____________ than predicted.
Practice Problems
77. Determine the van’t Hoff factor for the following solutions.
a. 0.25 M KCl
b. 0.0017 M CaCl2
c. 1.116 M C6H12O6
d. 0.075 M (NH4)2SO4
Concentration Units
All concentration units are a ratio of the amount of ____________ divided by either the amount of solvent or the amount of ____________.
Because molarity is based on the ____________ of the solution and because ____________ changes can result in volume changes, the molarity of a solution can change with temperature even when no other changes are made to the solution. When an experiment involves temperature changes, the unit ____________ is often used instead of molarity.
With mole fraction, no distinction is made between the ____________ and the ____________ in the calculations; the mole fraction of every component of the solution is calculated the same way. The sum of mole fractions for all solution components (the solvent and all solutes) is equal to ____________.
When converting between concentration units, you can choose an arbitrary total amount of solution to begin the calculation. Remember that concentration is an ____________ property
Strategy to convert between concentration units:
1. Write out the concentration as a ratio showing all the ____________ in their entirety!
2. Convert the solute into the required unit.
3. Convert the denominator into the required unit.
4. Use the concentration ratio to calculate the new concentration unit.
5. ____________ is the link from going from mass to volume or volume to mass.
6. Remember that a ____________ is composed of a solvent & solute.
Practice Problems
44. Calculate the molarity and molality of 268.3 mL of a solution containing 0.5142 mol of CsCl and 197.5 g of water.
52. Calculate the mole fraction of each component in a solution that is 15.7% by mass methyl alcohol, CH3OH, in water.
Colligative Properties
Colligative properties of solutions are properties that depend on the ____________ of solute particles in the solution but do not depend on ____________. The concentration terms in the equations for various colligative properties pertain to all solute species present in the solution. So an electrolyte that dissociates into two ions will have ____________ the effect on colligative properties as a ____________ that remains as a single particle.
Vapor Pressure Lowering
The equilibrium vapor pressure of a liquid is the ____________ exerted by its gaseous phase when ____________ and ____________ are occurring at equal rates. To vaporize, solvent molecules must be present at the ____________ of the solution. When ____________ particles are present, they disrupt the ability of the surface molecules to ____________ by occupying some of the surface area available to solvent molecules and thereby ____________ the rate of solvent vaporization. Since the rate of ____________ is unaffected by the presence of solute, the net result is that the vaporization-condensation equilibrium is achieved with ____________ solvent molecules in the vapor phase. Substances that evaporate easily, and thus have a measurable vapor pressure, have relatively ____________ intermolecular forces and are said to be ____________.
Raoult’s law: The partial pressure exerted by any component of an ideal solution is equal to the vapor pressure of the component when it is ____________ multiplied by its ____________ in the solution.
If a solution is made up of two volatile components (such as two liquids), the total vapor pressure above the solution is the ____________ of the vapor pressures of each of the components. If the solute is an electrolyte, the ions are each included in the ____________ calculation.
Freezing Point Depression and Boiling Point Elevation
The boiling point of a liquid is the ____________ at which its vapor pressure is ____________ to ambient atmospheric pressure. Since the vapor pressure of a solution is ____________ due to the presence of nonvolatile solutes, it stands to reason that the solution’s boiling point will subsequently be ____________. Vapor pressure increases with temperature, so a solution will require a ____________ temperature than will the pure solvent to achieve any given vapor pressure
For a liquid to freeze and become a solid, the ____________ ordered molecules in the liquid phase must form an ____________ in the solid phase. The solute particles interfere with the process of making the orderly array of molecules and therefore prevent freezing from occurring at the liquid’s normal freezing point temperature
The values of Kf and Kb depend on the ____________, but Kf is larger than Kb for almost all solvents, which means dissolving a solute in most solvents will lower the freezing point more than it raises the ____________.
Note that you have to use concentration in ____________ for these because you have changing temperature.
If you know how many grams of a solute are dissolved in a given mass of solvent, the ____________ of the solute can be determined by measuring the freezing point or boiling point.
Osmotic Pressure
Diffusion-driven transfer of solvent molecules through a ____________ membrane is a process known as ____________. Solvent molecules will ____________ across the membrane in both directions. Since the concentration of solvent is greater in the pure solvent than the ____________, these molecules will diffuse from the solvent side of the membrane to the solution side at a ____________ rate than they will in the reverse direction. Therefore, if all other factors are equal, the volume of the liquid will ____________ on the solution side. The more concentrated the ____________, the higher the liquid level rises on the solution side.
Osmotic pressure is the amount of pressure required to maintain a ____________ concentration of solution when it is separated from a pure solvent by a semipermeable membrane. At this value, the solvent moves across the membrane at an ____________ rate in both directions.
Practice Problems
60. Calculate the vapor pressure of benzene, C6H6, at 25°C in an ideal solution containing 1.66 mol of benzene and 0.313 mol of toluene. The vapor pressure of pure benzene is 96.0 torr.
74. Calculate the osmotic pressure of a 0.0100 M solution of glucose in water at 25°C.
82. Calculate the boiling point of 0.150 m aqueous solutions of Mg(NO3)2
Text segments from OpenStax, Chemistry. OpenStax CNX. Sep 15, 2020 http://cnx.org/contents/[email protected].; White, J. et al. Interactive General Chemistry. MacMillan, NY. 2019.; Chemistry LibreTexts, Libretexts, [online] Available from: https://chem.libretexts.org/Courses/ Reading guide style Adapted from "Ionic equations Study Guide" by Montgomery College is licensed under CC BY 4.0 Document not to be reposted on the internet without express permission.
