Chapter 11 Text
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Homogeneous mixtures can be classified according to the size of thei constituent particles as either __ or __.
What are solutions?
- the most common class of homogeneous mixtures
Solutions are __, thoiugh they may be __, and they dont __.
- separate on standing
__, like milk and fog, contain much larger aprticles. Although they are often __, they don't __
- murky or opaque to light
- separate on standing.
Mixtures called __ also exist, having even larger particles than colloids. These are not truly __, because their particles __ and are visible with a low-power microscope. ONe example is blood.
- separate out on standing
For solutions in which a gas or solid is dissolved in a liquid, the dissolved substance is called the __ and the liquid is called the __. When one liquid is dissolved in another, the minor component is usually considered the __ and the major is hte __.
What are the three interactions among particles that have to be taken into account in solution
True or False
What is solvated/ hydrated?
they are surrounded and stabilized by an ordered shell of solvent molecules
If delta G is negative, the process is __ and the substance __.
The enthalpy change is called the __ and the etropy change is called the __.
- heat of solution
- enthalpy of solution
- entropy change
- entropy of solution
Entropies of solution are usually __ because the molecular randomness usually incresaes during dissolution.
Explain solvent-solvent interactiosn.
energy is absorbed to overcome intermolecular forces between solvent molecules because the molecules must be separated and pushed apart to make room for solute particles
Substances with higher lattice energies tend to be __ than substances with lower lattice energies.
Explain solvent-solute interactions.
energy is released when solvent molecuels cluster around solute particles and solvate them
For ionic substances in water, the amount of hydration energy released is generally __ for smaller cations than for larger ones because water molecuels can approach the positive nuclei of smaller ions more closely and thus bind more tightly. In addition, hydration energy generally __ as the charge on the ion increses.
The first two kinds of interactions are __, requiring an input of energy to spread apart solvent molecules and to break apart crystals. Only the third is __, as attractive intermolecular forces develop between solvent and solute aprticles.
Is molarity temperature dependent or independent?
are mole fractions dependent or independent of temp?
How do you get mass percent?
mass of component/ total mass of solution x 100
Closely related to mass percent, and particularly useful for very dilute solutions, are the concentration units __ and __.
- parts per million (x 10^6)
- parts per billion (x 10^9)
A concentration of 1 ppm for a substance means?
For dilute aqueous solutions near room temp, where __ has a volume __, 1 ppm alsom means __.
- that each kilogram of solution contains 1 mg of solute
- 1 kg
- 1 L
- each liter oof solution contains 1 mg of solute
What is the advantage of using mass percent for expressing concentration?
the values are independent of temperature because masses dont change when substances are heated or cooled
What is the disadvantage of using mass percent for expressing concentration?
it is generally less convenient when working with liquid solutions to measure amounts by mass rather than by volume abd the density of the solution must be known
What is molality?
- the number of moles of solute per kilogram of solvent
- moles of solute/ mass of solvent in kg
Advantage of using molaily?
it is temperature-independent because masses don't change when siubstances are heated or cooled
What is the disadvantage of using molality?
amounts of solution must be measured by mass rather than by volume and that the density of the solution must be known to convert molality into molarity
The definition for saturated requires that a saturated solution be at __ with undissolved solid at a given temp.
A supersaturated solution is __ and __ occurs when a tiny seed crystal of (if working with NaCl) sodium acetate is added to initiate __.
The solubility of a substance-- that is, the amount of a substance per unit volume of solvent needed to form a saturated solution at a given temp-- is a __ property of that substance
Sometimes, particularly when two liquids are involved, the solvent and solute are __, meaning that they are mutually soluble in all proportions. A solution of __ and __ is an example.
- ethyl alcohol
Solubilities are __, meaning.
- the temp at which a specific measurement is made must be reported
The solubilities of most __ and __ solids __ with increasing temperature, althoguh the solublities of some (NaCl) are alomost __ and the solubilties of others __.
The effect of temp on the solubility of gases is more predictable that its effect on the solids: __
gases become less soluble in water as temp increases
__ has practically no effect on the solubility of liquids and solids, but has a profound effect on the solubility of gases.
the solubility of a gas in a liqid at a given temp is directly proportional to teh partial pressure of the gas over the solution
When the gas partial pressure P is 1-atm, the Henry's Law constant k is __.
numerically equal to the solubility of teh gas in moles per liter
On a molecular level, the increase in gas solubility with increasing pressure occurs because __
of a change in the position of the equilibrium between dissolved and undissolved gas
At a given pressure, an equilibrium is estabilished in which __.
When the pressure is increased, however, __
- equal numbers of gas partiles enter and leave the solution
- more particles are forced into solution than leave it, so gas solubility increases until a new equilibrium is established
The __ BP and __ FP observed for a solution compared to a pure solvent are examples of __, which depend only on the amount of dissolved solute but not on the solute's chemical identity.
- colligative properties
What are the four colligative properties?
- the vapor pressure of the solution is lower
- the BP of the solution is higher
- the freezing or melting point of the solution is lower
- the solution gives rise to osmosis, the migration of solvent molecuels through a semipermeable membrane
A liquid in a closed container is in equilibrium with __ and that the amount of pressure exerted by the vapor is called the __.
If the solute is nonvolatile and has no appreciable vapor pressure of its own, as occurs when a solid is dissolved, then the vapor pressure of hte solution is always __ then that of the pure solute.
If the solute is voltaile and has a significant vapor pressure of its own, as occurs in a mixture of two liquids, then the vapor pressure of the mixture is __ between the vapor pressures of hte two pure liquids.
True or False:
A solution always evaporates more quickly than a pure solvent does because its vapor pressure is lower and its molecules therefore escape less readily.
- A solution always evaporates more quickly slowly than a pure solvent does because its vapor pressure is lower and its molecules therefore escape less readily
- the vapor pressure of a solution containing a nonvolatile solute is equal to the vapor pressure of hte pure solvent times the mole fraction of the solvent
- Psoln=Psolv x Xsolv
If an ionic substance such as NaCl is the solute rather than a molecular substance, what must we do?
calculate mole fractions based on the total concentration of solute particles (ions) rather than NaCl formula units
What does Raoult's law only apply to?
ideal solutions; the law works best when solute concentrations are low and when a solute and solvent particles have similar intermolecular forces
If the intermoleuclar forces between solute particles and solvent molecules are weaker than the froces between solvent molecules alone, then the __.
solvent molecules are less tightly held in the solution and hte vapor pressure is higher than Raout's law predicts
Solutions of ionic substance often have a vapor pressure significantly __ than predicted, because the __ between dissolved ions and polar water molecules are so strong.
True or False:
Ionic substance rarely dissociate completely
The actual extent of dissociation can be expressed as a __.
van't Hoff factor (i)
A physical process such as the vaporization of aliquid to a gas is accompanied by a __.
- free-energy change
- DetaGvap= DeltaHvap - TdeltaSvap
The more negative the value of deltaGvap, the more __
favored the vaporization process
The vaporization of a liquid to a gas is disfavored by __ because energy is required to overcome intermolecular attractions in the liquid. At the same time, however, vaporization is favored by __ because randomness increases when molecules go from a liquid state to a gaseous state.
- enthalpy (positive deltaHvap)
- entropy (positive deltaSvap)
The __ of vaporization for a pure solvent and a solvent in a solution are similar because similar intermolecular forces must be overcome in both cases for solvent molecuels to escape from the liquid.
The __ of vaporization for a pure solvent and a solvent in a solution are not similar, however, Because a solvent in a solutoin has more molecular randomess and higher entropy than a pure solvent does, the entropy change on going from a liquid to vapor is __ for the solvent in a solution than for the pure solvent.
Because a solution of a nonvolatile solute has a lower vapor pressure than a pure solvent has at a given temperature, what must happen to the solution?
must be heated to ahigher temp to cause it to boil
The lower vapor pressure of hte solution means that the liquid/ vapor phase transition line on a __ is always lower for the solution than for the pure solvent.
As a result, the triple-point temperature Tt is __ for the solution, the solid/ liquid phase transition line is shifted to a __ temperature for the solution, and the solution must be cooled to a __ temperature to freeze.
The boiling point elevation of a soltuion relative to that of a pure solvent depends on the concentration of __, just as vapor-pressure lowering does.
The change in BP (deltaTb) for a solution is __. Freezing is similar, except for boiling, substitute freezing
- deltaTb=Kb x m
- where m is the molal (not molar) concentration of sollute particles and Kb is the molal-boiling-point-elevation constant characteristic of a given liquid
To take dissociation into account, what must be added to the two equations of change in boiling/ freezing point
In comparing the __ for a pure solvent and for a solvent in a solution, the values are similar because similar intermolecular forces holding the solvent molecules must be overcome in both cases. In comparing the __ of vaporization, however, the values are not similar. Because the solvent in a soltuion has more molecular randomness than a pure solvent has, the __change betaween solution and vapor is smaller than the __change between pure solvent and vapor.
- entropy x2
If deltaSvap is smaller for the solution, then __ must be correspondingly larger. In other words, the __ of the solution is higher than that of the pure solvent.
In comparing the solvent in a solution with a pure solvent for freezing, the __ are similar because similar intermolecular forces between solvent molecules are involved. The __ are not similar. Because the solvent in a solution has more molecular randomness than a pure solvent has, the entropy change between the solvent in the solution and the solid is larger than the entropy change between pure solvent and the solid. With __ larger for the solution, __ must be correspondibgly smaller, meaning that the freezing point of the solution is __ than that of the pure solvent.
- enthalpies of fusion (deltaHfusion)
- entropies of fusion (deltaSfusion)
The amount of osmotic rpessure at equilibrium depends on the __.
- concentration of solute particles in the solution according to the equation II=MRT
- m= molar concentration of solute particles
- R= gas constant
- T= temp in K
How would you prepare a solution of methyl alcohol and water in which Xmethanol is 0.15 and Xwater is .85
mix together .15 mol of methanol with .85 mol of water
Why does 5 g of powdered NaCl dissolve rapidly as opposed to 5 g block?
the larger the surface area, the more solid-solvent interactions, adn the more rapidly it dissolves
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