Chapter 13: Solutions
Solution Formation: IMFs and Entropy 1. What is entropy? 2. Which state of matter has the highest entropy? 3. Which has a higher entropy: solution or pure solute and pure solvent? 4. An increase in entropy is the ________ in both physical and chemical processes. 5. What are the equations for when liquid vaporizes and when liquid freezes?
1. Entropy (S) of a system is related to the number of ways a system can disperse its energy and therefore to the freedom of motion of the particles 2. Gases has the highest entropy then liquid then solid 3. a solution! 4. the natural tendency 5. -ΔSvap =S(g)- ΔS(l) (ΔSvap>0) -ΔSfus =S(l)- ΔS(s) (ΔSvap<0) * another factor that determines whether a solute dissolves
Concentration ratio and symbol for molarity and molality?
1. Molarity (M) = amount (mol) of solute/ volume (L) of solution 2. Molality (m) = amount (mol) os solute/ mass (kg) of solvent
Concentration ratio for mole fraction and mass percent?
1. Mole fraction (X) = amount (mol) of solute/ [amount (mol) of solute +amount (mol) of solvent] 2. Mass percent = mass of solute/ mass of solution
Osmotic Pressure: 1.What is it? 2. Why does it occur? 3. What is the equation and components?
1. Osmotic pressure is the pressure that must be applied to prevent the net flow of solvent (compensates for different liquid heights or to prevent increase in volume) 2. always looking to keep an equilibrium (rate into solution = rate out of solution) 3. π = MRT - M = molarity (mol solute/L soln) - R = 0.0821 atm x L / mol x K - T = Kelvin temp
What is a solute?
is the substance that is dissolved (usually the substance present in a smaller amount)
What is solubility?
it is the max amount of solute that dissolves in a fixed quantity of a particular solvent at a specific temp. -qualitative term
The vapor pressure of a solution containing a __________ __________ is always lower than the vapor pressure of a pure solvent.
nonvolatile, nonelectrolyte
What does BP generally correlate with in water?
solubility! *weak intermolecular forces = low BP
Molality involves quantity of _____, whereas the other concentration terms involve quantity of soluntion
solvent
What is the freezing point depression proportion to of the solution?
the molality Eq: ΔTb = Kbm - Kb is the molal boiling point elevation constant for the solvent *can be switched out for f to find freezing point depression (Kb water = 0.512 and Kf = 1.86)
If it requires more energy to break apart the solute and solvent particles than is given off by solute-solvent interactions the solvation process would be? A. Endothermic B. Exothermic C. Impossible to tell
ENDOTHERMIC
What is the difference between enthalpy and entropy?
Enthalpy: the sum of internal energy of a system and the product of the pressure and volume of a system Entropy: is a measure of disorder or randomness of a system (ordered system low entropy)
What are Nonideal Situations?
Ions may remain clustered together in solution, forming an atmosphere. This effect is greater for a more concentrated solution. ???
What happens when table sugar or sucrose dissolves in water?
It breaks into smaller particles!!! (is not: no longer present in the solution, dissociated in water, an electrolyte, forming ions in solution)
What happens when a solute is first added to the solvent?
It is faster at first!
What is osmosis?
It is the movement of solvent particles from a region of higher to a region of lower concentration through a semipermeable membrane *solvent will always flow from a more dilute solution to a more concentrated one!!!
What do we want regarding entropy and enthalpy for solution formation?
Lower enthalpy and higher entropy
What is solvation ?
Solvation = the process of surrounding a solute particle with solvent particles ΔHsolvation = ΔHsolvent + ΔHmix
What does "like dissolves like" mean?
Substances with similar types of intermolecular forces dissolve each other ex: polar dissolves polar and non-polar dissolves non-polar
The temperature when Pvap = Pext is?
Temperature boiling point
What effects the strength of ionic bonds?
The size first and then the "charge capacity" ( how much space)
What affects the magnitude of ΔHhydration?
The smaller the ion than the stronger the attraction to water!!! KINDA CONFUSED
What is Henry's Law?
The solubility of a gas (Sgas) is directly proportional to the partial pressure of the gas (Pgas) above the solution Equation: Sgas = KH X Pgas -units: -Sgas =mol/L -KH= mol/L x atm or mol x L^-1 x atm^-1 (constant) - Pgas = atm
What is a nonvolatile solute?
The solute added won't evaporate
Aqueous: 1. What does in mean on a particulate level?
aqueous means dissolved in water and that the ions are dissociated with each other and become hydrated
How does the addition of a solute ( thus lowering the VP of the solvent/solution) affect boiling and freezing point?
boiling point: solute addition makes BP increase because (higher temp) freezing point: solute addition makes FP decrease (lower temp) WHY?????
When water comes in contact with NaCl what attractions are broken and which ones form?
broken: the dipole-dipole attraction form: ion-dipole attraction forms *the oxygen is attracted to cations and the hydrogen attracted to anion
What is solvation in water called?
hydration ΔHhydration = ΔHsolvent + ΔHmix ΔHsolvent = endothermic (+) ΔHmix = exothermic (-) ΔHhydration = ALWAYS exothermic (-) *this is bc heat of hydration is a key factor in dissolving an ionic solid
When you have grease on your hands it can't be dissolved by water so....
we need soap!!!! -soaps cleaning ability depends on the dual polarity of its molecules has cleaning ability (polar-ionic heads attach to water and nonpolar tails dissolves grease)
What are the components of aqueous ionic heat of solution?
ΔHsoln = ΔHsolute + ΔHhydration ΔHsoln = ΔHlattice + ΔHhydr of ions *ΔHsolute =ΔHlattice...... which are both always positive! but combined heats with hydration of the ions which is always neg.
How can we rewrite enthalpy quantities when: ΔHsoln = ΔHsolute + ΔHsolvent + ΔHmix ΔHsolvation = ΔHsolvent + ΔHmix
ΔHsoln = ΔHsolute + ΔHsolvation
What are the three steps of dissolving a solute in a solvent that are each accompanied by enthalpy?
*before solution: solute particles attracting each other and same with solute particles 1. solute particles separate from each other (endothermic) - solute (aggregated) + heat = solute separated - ΔHsolute > 0 2. Solvent particles separate from each other (endothermic) - solvent (aggregated) + heat = solute separated - ΔHsolute > 0 3. solute and solvent particles mix and form a solution (exothermic) - solute (separated) + solvent (separated) = solution + heat - ΔHmix < 0 OVERALL: thermochemical solution!!! (aka sums of all ΔH and + or - depends on relative sizes of ΔH values) ΔHsoln = ΔHsolute+ΔHsolvent+ΔHmix
Why does vapor pressure lowering (ΔP) occur in regard to entropy?
- compared to the pures solvent, fewer solvent particles in the solution have to leave (vaporize) to achieve the same entropy as the solvent we end up with fewer particles in the vapor phase THUS a lower vapor pressure
What type of attractions must be overcome to melt NaCl(s)? why?
- dispersion because its more only when its broken apart not together as an ion!
What does the concept "like dissolves like" mean?
- if the intermolecular forces between the solute molecules are similar to the intermolecular forces between the solvent molecules, then the solvent will have favorable interactions and dissolution will generally occur BUT if intermolecular forces are different then the solute will most likely be insoluble - ex: NP hexane couldn't dissolve in polar water but salt could be!
What is a solution?
-a homogeneous mixture with a uniform composition throughout - can be solids (brass) , liquids or gases (air) -composed of a solute and solvent through intermolecular forces
Equilibrium on a Particulate Level?
-at some temperature, the number of solute particles dissolving per unit time equals the number recrystallizing - solute (undissolved) = solute (dissolved)
What is dispersion intermolecular force?
-everything has this! only will see with two nonpolar molecules though!
What is an ion-induced dipole intermolecular force?
-ions charge disorts the electron cloud of a nearby non-polar molecule
What is a solvent?
-is the medium in which the solute is dissolved (ex. salt dissolved in water) - most abundant *sometimes "solute + solvent" loose meaning and substances become miscible (soluble in any proportions)
What is an ion-dipole intermolecular force?
-it is the strongest force -ionic compound dissolves in water -two events simultaneously: 1. forces compete (water attractions overcome ion attractions) 2. hydration shells form (as ion separates water molecules for these, and number of H2O molecules depends on ions size)
How does pressure affect gas solubility?
-major effect!... when volume decreases and gas pressure increase the gas particles collide with the liquid surface more often THUS more particles enter than leave the solution per unit time *little effect on solid and liquid because almost incompressible
What is equilibrium vapor pressure?
-partial pressure exerted by vapor particles in a closed system -with solvent molecules: equilibrium is reached with a given number of particles in the vapor -with nonvolatile solute molecules: equilibrium is reached with fewer particles in the vapor
What is an H bond intermolecular force?
-polar molecules with H attached to either an O, F, N -ex alcohols or amino acids
What are electrolytes?
-substances that when mixed with water conduct electricity -electrolytes produce ions in aqueous solution (we say they dissociate into ions)
What does vapor pressure lowering depend on?
-vapor pressure lowering depends on the amount of solute, NOT ITS IDENTITY, so enthalpy (IMFs) can't explain it
What is an dipole-induced dipole intermolecular force?
-when a polar molecule disorts the electron cloud of a non-polar molecule (negative pushing away negative electron cloud)
What is the differences between saturated solutions, unsaturated solutions, and supersaturated solutions?
1. Saturated solutions: contains the maximum amount of dissolved solute at a given temp in the presence of undissolved solute (equilibrium) 2. Unsaturated solution: contains less than the equilibrium concentration of dissolved solute. If more solute is added, it will dissolve. 3. Supersaturated solution: contains more than the equilibrium concentration of dissolved solute
Compare in regard to entropy: (S - vapor pressure) 1. Ssolvent vs. Ssolution 2. Svapor vs. Ssolvent
1. Ssolvent < Ssolution 2. Svapor >> Ssolvent Therefore in order of increasing entropy: Svapor>>>> Ssolvent > Ssolution
What two factors play a role in a solution forming?
1. The attractive forces between solute and solvent are as strong as the attractive forces between solute particles and between solvent particles 2. Increase in entropy (the number of ways energy can be dispersed through the motions of its particles)
Heat of Solution (ΔHsoln) 1. Breaking bonds or intermolecular attractions is________. 2. Forming bonds or intermolecular attractions is _______.
1. endothermic 2. exothermic
Describing Solutions: Solubility 1. The solution is ______ to increase the solute's solubility. 2. When it is cooled slowly, the solubility goes _____ what is dissolved, but the _______ remains dissolved 3. The solution is _____ and addition of ___________ causes excess solute to precipitate 4. Example?
1. heated 2. below, solute 3. unstable, tiny crystal or a jolt to the beaker 4. hot pack!
What are the 6 types of intermolecular forces in a solution in order from strongest to weakest attraction?
1. ion-dipole 2. H bond 3. dipole-dipole 4. ion-induced dipole 5. dipole-induced dipole 6. dispersion *attractions always there but the intermolecular force could not be @ work *peep diagrams in your notes
Trends in Ionic Heats of Hydration: 1. What happens when ΔHhydr as ions get bigger within a group? 2. What happens to ΔHhydr as charge increases? 3. Which seems to affect ΔHhydr more charge or size?
1. it goes down 2. it goes up 3. depends on the charge density (ratio of charge to volume) but usually the charge * More charge packed in a smaller space makes a stronger attraction to a water molecule!
How does temperature affect solubility of gases and solid solutes in water?
1. most solids are soluble at higher temperatures (its easier to break ionic bonds) 2. gas solubility is more predictable... so gas solubility in water decreases with rising temperatures (this is because gases have weak IMF with water, so as temp rises avg. KE increases allowing the gas particles to easily overcome these forces and re-enter the gas phase!)
1. Molality is based on mass so? 2. The mole fraction give the proportion of?
1. so it is independent of temp 2. gives the proportion of dissolved particles
What happens if solute particles: 1. enter the gas phase 2. enter the solid phase 3. move across a semipermeable membrane
1. solute particles enter the gas phase = in ΔPvap (vapor pressure decrease) and ΔTb (boiling point increase) 2. solute particles enter the solid phase = ΔTf (freezing pt. decrease) 3.solute particles move across a semipermeable membrane results in π (osmotic pressure)
Volute Solutes: 1. For a volatile non electrolyte, what does the vapor of the solution contain? 2. How does the volatile component affect VP?
1. the solution contains both solute and solvent (vapor has a different composition than the solution) 2. the presence of each volatile component lowers the VP of the other, since each one lowers the mole fraction of the other (for a solution the vapor will have a higher mole fraction of the more volatile component)
Solute particles: 1. What can't they do? 2. What has a bigger effect?
1. they cant move between two phases!!!! 2. the more solute there is the bigger the effect!
What are the two types of compounds that are electrolytes?
1.Ionic (strong electrolytes, soluble) 2. Acids (weak electrolytes, don't dissociate completely) *non electrolytes = molecular compounds!
Which of the following compounds dissociate into ions when dissolved in water? A. Copper (2) nitrate B. Table sugar (C11H22O11) C. Ethylene glycol (HOCH2CH2OH) D. HNO3
A and D!!!! *DISSOCIATE means to break into ions and DISSOLVE just means to break into smaller pieces!
Which best explains why a solute with an endothermic heat of solution (such as ammonium nitrate) even dissolves in water? A. the entropy of mixing is much greater than the increase in enthalpy B. the entropy of mixing is much less than the decrease in enthalpy A. the entropy of mixing is much greater than the decrease in enthalpy A. the entropy of mixing is much less than the increase in enthalpy
A!!! * it is unfavorable for the reaction to be endothermic because you want to be releasing heat!!!
A. CaCl2 (s) = Ca2+ (aq) + 2Cl(aq) B.NH4Cl(s) = NH4+(aq) + Cl(aq) In these two solution formations which is exothermic and which is endothermic? Whats easier to separate? What are the temperatures of the bag?
A. exothermic!, hot bag!, negative ΔHsoln B. endothermic, cold bag!, weaker so easier to separate!, positive ΔHsoln
When a saturated solution is in equilibrium with undissolved solid solute..... A. the dissolving and crystallizing processes continue to occur B. the addition of one more crystal of solute will not change the solution concentration C. the concentration of the solution is constant D. all of the above
ALLL OF THE ABOVE!!!!
Ethane gas, C2H6, is bubbled into liquid heptane, C7H16. It is logical to expect that the gas will: A. dissolve because both molecules undergo hydrogen bonding B. dissolve because both molecules are non-polar C. not dissolve because ethane is non-polar and heptane is highly polar D. not dissolve because ethane is a gas and heptane is a liquid
B!!!!
Which of the following is the BEST explanation for why AGCl is insoluble in water? A. Water and AgCl do not have similar types of intermolecular forces B. Water is polar and AgCl is nonpolar C. The amount of energy given off by solute-solvent interactions is not enough to overcome the ionic bonds in AgCl
C!!!!
Rank the following in order of increasing freezing point.... glucose, CaCl2, NaNO3 * all are 0.100m aqueous solutions
CaCl2 < NaNO3 < Glucose
What is the difference between a cation and anion?
Cation = positively-charged ions Anion = negatively-charged ions
What are solution properties depending on the quantity of solute particles called?
Colligative Properties
What don't oil and water molecules not mix?
Oil and water don't mix because water molecules are more attracted to each other than to oil molecules. (it is insoluble in water but not in hexane!)
What does Van Hoff's factor tells us and the role it plays in calculations with colligative properties?
The Van Hoff factor takes into account the dissociation of a strong electrolyte to predict the effect of the solution i = (measure value of electrolyte solution/ expected value for nonelectrolytes) *the formula of the compound indicates the expected number of particles in solution
If solutes affect vapor pressure do boiling points?
The temperature at which the VP of the liquid is equal to the pressure above its surface is known as *as temperature increases so does boiling point at a constant vapor pressure
What is Raoult's law?
This law states that the VP of the solvent above the solution is proportional to the mole fraction of the solvent present! Eq: Psolvent = Xsolvent x Psolvent -Xsolvent = (mol H20/ mol H20 + solute) - Psolvnet = pure solvent (like pure water) *the VP lowering is proportional to the mole fraction of the solute present: Eq- ΔPsolvent = Xsolute x Psolvent
The greater the charge density = the ________ ΔHhdyra
more negative!
What is reverse osmosis?
movement of solvent particles from a region of lower to a region of higher concentration through a semipermeable membrane with REQUIRED ENERGY
