Unit 6

Question 1

our tap water is considered what type of a solution?

Answer 1

Aqueous solution

Question 2

Solutes and solvents can be

Answer 2

any state of matter—solid, liquid or gas.
-When solute particles become evenly distributed, the entire solution takes on the physical state of the solvent
-liquid solutions are transparent to light and have very small solute particles that cannot be separated from the solvent by filtration

Question 3

colloids

Answer 3

-intermediate sized solute particles form colloids whose particles may be individual large molecules or clusters of molecules (aggregates)
-The properties of liquid colloids are similar to liquid solutions in that the particles are so small and evenly dispersed in the dispersion medium that they will not separate upon standing and are not filterable.
-Many colloids look uniform and identical to solutions to our eyes because individual particles are not seen while others are murky in appearance.
-Light passes directly through solutions, yet as light passes through a colloid, the particles scatter the light and the beam can be seen due to the Tyndall effect.

Question 4

suspensions

Answer 4

-larger particles dispersed in a medium are visible and form heterogeneous mixtures called suspensions.
-Most suspensions are solids dispersed in liquids; however, suspensions may form between two liquids or a solid or liquid dispersed in a gas.
-Liquid suspensions may scatter light or have a murky to opaque appearance and the particles can be separated from a liquid suspension by filtration.
-Many drug preparations are in the form of suspensions and must be shaken well before a dose can be measured out since the particles are unevenly dispersed, or “suspended,” and large enough to fall to the bottom of the container due to gravity.

Answer 5

Question 6

Aqueous solutions are

Answer 6

Homogenous mixtures made of a majority of the solution as the solvent

Question 7

The strength of the interactions between the solute and solvent

Answer 7

must overcome the individual solute-solute and solvent-solvent interactions to form a solution.

Question 8

miscible

Answer 8

If the solute and solvent are both liquids having similar intermolecular forces, and they can easily form a solution, they are said to be miscible in each other.

Question 9

Solubility

Answer 9

-Molecules with a large surface area are more soluble in a given solvent than those with smaller surface areas. -Molecules that can have more points of contact between individuals will have more attractive forces between them (either solute-solute or solute-solvent interactions)

Question 10

Non-polar Solvents and Solutes

Answer 10

-interact with each other through numerous London dispersion forces between individual molecules so that instantaneous and temporary dipoles in the solute and solvent molecules align themselves to maximize and maintain the short-lived opposite attractions forming the solution. -Organic compounds containing only carbon and hydrogen atoms are non-polar and are only soluble in non-polar solvents such as hexane (C6H14) and benzene (C6H6).

Question 11

Polar Solvents and Solutes (1/2)

Answer 11

-Polar solvents will orient themselves so that the negative dipole of one molecule is adjacent to the positive dipole of a solute molecule and vice versa until each solute molecule is free from its neighbor and evenly distributed within the solvent.
-They interact with each other usually by multiple dipole-dipole forces as solute molecules are surrounded by solvent molecules to form a solution

Question 12

Polar Solvents and Solutes (2/2)

Answer 12

-solvents with high polarity will dissolve solutes that are highly polar; slightly polar solvents would be more suited for dissolving less polar solutes. -Smaller polar molecules dissolve in polar solvent such as water with more ease than larger polar molecules–NH3 is more soluble than CH3CH2Cl in water.
-When comparing molecules of the same size, those that can form hydrogen bonds with water will be more soluble than those that cannot. -For example CH3OH (methanol) is more soluble in water than CH3Cl, because the methanol can form H-bonds with water molecules.

Question 13

“solvation” or “dissolution”

Answer 13

Physical process
-Only the interactions between individual molecules are disrupted upon solution formation and replaced by new interactions.
-Since solutions are formed by physical means, components of solutions can be separated from each other by physical means.

Question 14

Dissolution

Answer 14

Physical process
-Governed by entropy and enthalpy changes
-When the entropy and enthalpy changes are favorable (energetic favorability) a solute will dissolve spontaneously
-solutes that will not dissolve spontaneously under any conditions are considered insoluble
-dissolving a solid solute is an entropically favorable event since the solid particles become free of the confines of the solid crystal structure and can move about unrestricted in solution

Question 15

Endothermic or exothermic

Answer 15

-Depending on whether there is a net release or absorbance of energy when solute molecules dissolve in a solvent, solvation can be an endothermic or exothermic process.
-Energy is required and absorbed to disassociate solute molecules from each other and disrupt their intermolecular forces or to disrupt the attractive forces between cations and anions.
-Energy is released when the solute and solvent particles form attractions between each other.
-Some solutes will release more energy upon dissolution, and it will be an exothermic process.
-Other solutes absorb more energy when forming interactions between solvent molecules and dissolution is an endothermic process.

Question 16

Water, universal solvent

Answer 16

-The unique properties of water allow it to be the “universal” solvent in chemistry allowing it to dissolve a wide range of polar molecules and even ionic compounds.
-However, many organic compounds are not soluble in water.
-Water is required for life and makes up over 70% of the human body.
-Water acts as the solvent for all of the biochemical reactions within cells and at times is a reactant or product of such reactions.
-It is also the medium that facilitates the transport of ions, nutrients and wastes into and out of cell

Question 17

Polar aqueous solutions

Answer 17

-Water forms aqueous solutions via dipole-dipole interactions between individual water molecules and polar solute molecules.
-The negative dipole on the oxygen in water will attract any positive dipole on a solute molecule, while the positive dipole on the hydrogen atoms will attract any negative dipole on another solute molecule.
-Many polar solutes contain -OH or -NH bonds that will allow for hydrogen bond (H-bond) formation between themselves and water molecules.
-In fact, the more of these -OH and -NH bonds found within a large molecule, the more polar it will become and its solubility increases in water.
-Larger molecules with fewer of these types of bonds will be less polar and have decreased solubility in water.
-atoms within the molecule do not separate upon dissolving.

Question 18

Ionic Aqueous Solutions

Answer 18

-The attractive forces or interactions between ions and water molecules can be referred to as ion-dipole interactions.
-By dissolving, the ions in an ionic compound dissociate from each other or “solvate.”
-The dissolved ions are said to be “hydrated” when they become surrounded by water molecules—O-atoms oriented towards cations with H-atoms oriented towards anions. -When the dissolved ions are evenly distributed throughout the water a uniform aqueous ionic solution forms.
-some ionic compounds will dissolve in water under only certain conditions (ex. With heat) and only to a very small extent.
-Such ionic compounds will settle to the bottom of a container filled with water forming a “precipitate.”
-no amount of heat or stirring will dissolve these compounds and they form a heterogeneous mixture, not a solution

Question 19

Electrolyte vs non-electrolyte

Answer 19

An electrolyte is a substance that dissolves in water and the ions allow the solution to conduct electricity. A non-electrolyte is a substance that dissolves in water but does not conduct electricity.

Question 20

Electrolytes

Answer 20

-Only aqueous solutions that contain electrolytes, or dissolved ions, can conduct electricity.
-The more ions in solution, the greater the conductivity.
-Thus, all soluble salts are “strong electrolytes” and will dissolve completely in solution—every formula unit dissociates into its ions.

Question 21

Weak electrolytes

Answer 21

-a term also applied to salts that are slightly soluble.
-The “weak” designation refers to poor formation of ions in water.
-Although a weak electrolyte solution can light up a light bulb, the light is dim compared to the bright light given off by a strong electrolyte.
-Only a few units of each compound will dissociate into their respective ions, while the majority will remain locked into the solid crystalline structure.
- This can be noted as forward and reverse arrows when writing the equations for their dissolution below to represent that both dissolution and recrystallization are occurring at the same time and same rate.

Question 22

Non-electrolytes

Answer 22

-do not dissociate into ions when dissolved in water.
-most molecular compounds do not dissociate into ions, nor separate into their constituent atoms upon dissolving in water and are non-electrolytes.
-Salts that are insoluble in water are also considered non-electrolytes since they do not dissolve into ions in water. -No dissociation into ions means no electrolyte formation.

Question 23

Solubility

Answer 23

-Only solutes with similar intermolecular forces will dissolve in a given solvent.
-Solubility is the maximum amount of solute capable of dissolving in a particular solvent.
-Solubility is represented numerically as:
Grams of solute/ 100 mL of solvent
-Solutes will dissolve in particular solvents based on a number of factors: similarity of solute and solvent intermolecular forces, temperature; and pressure.

Question 24

Temperature

Answer 24

-Temperature changes affect how well molecules of a pure substance interact with each other
-Increased vibrations at higher temperatures will cause particles to move faster and collide into each other more often.
-As solvent molecules bump into clusters of solute molecules more at a faster rate, they form solute-solvent attractions leaving their solute-solute and solvent-solvent attractions behind. -Increasing the temperature will increase the solubility of a liquid or solid solute in a given solvent.
-Solubility limits are given for individual solutes in a given solvent at a specific temperature.

Question 25

Temperature for a gaseous solute

Answer 25

-Increasing the temperature of a solution containing a gaseous solute will decrease the solubility of the gas in the solution
-Gas molecules have virtually no interactions between each other, but when condensed they can be forced to dissolve in liquid solvents.
-High temperatures increase the vibration of gas molecules within the solution, allowing them to expand and readily break free from their attractions to the solvent molecules at a higher rate than at low temperatures. -Gases are more soluble in liquid solvents at lower temperatures than high temperatures.
-Dissolving of gas molecules involves a loss of entropy as gas molecules essentially become liquid.
-This process is less spontaneous at high temperatures
-at low temperatures, the kinetic energy of molecules decreases, and as a gas becomes a liquid it will more readily dissolve in a solvent.

Question 26

Pressure

Answer 26

-Pressure usually has no effect on liquid solutions unless the solute is a gas
-Henry’s Law explains the behavior of gaseous solutes under different pressures.
-The law states that the solubility of a gas in a liquid solvent is directly proportional to the partial pressure of the gas above the solvent liquid.
-The partial pressure of the gas is essentially the concentration of a gas. -The higher the partial pressure, the more a gas will dissolve in a solvent at a given temperature.
-Decreasing the pressure of a gas will decrease its solubility.
-If more than one gas is dissolved in solution, increasing the partial pressure of one gas will increase its solubility, not the solubility of the other gases.
-Increasing the partial pressure of one gas will actually decrease the solubility of another gas in solution since they will be “competing” for space in the solvent.

Question 27

Saturated Solutions

Answer 27

-When liquids are completely soluble in each other regardless of the relative amounts, they are said to be “miscible.” -There is no limit to the amount of solute or solvent that will mix with each other; they are mutually soluble in all proportions.
-If a solid can dissolve in a given liquid solvent, only a certain amount will dissolve completely at a given temperature.
-This is considered the saturation limit, defined as the measurement of the amount of solute in 100 mL of solvent. -Any additional solute added to the solution above this limit will not dissolve and drop to the bottom of the container.
-A saturated solution forms containing the maximum amount of solute capable of dissolving at a given temperature; it does not have the capacity to dissolve any more solute.

Question 28

Unsaturated solutions

Answer 28

-can dissolve more solute if added to the solution up to the saturation limit. -Remember that solubility is temperature dependent and more solute can be added to solvents at a higher temperature than at lower temperatures.
-If the temperature of an unsaturated solution decreases, the solute will recrystalize forming a saturated solution
- There are some salts that are exceptions to this and are more soluble at cold temperatures

Question 29

Supersaturated solution

Answer 29

-Under specific conditions, a supersaturated solution can form containing more solute than the saturation limit at a given temperature. -Heating the solvent and saturating it with solute, then cooling slowly will form a supersaturated solution.
-If the process is not done carefully enough or the system is disturbed by striking the container or adding a small crystal of the solute, the excess solute will precipitate out of solution forming crystals.
-This process is called crystallization, or recrystallization since a solid is first dissolved in a solvent then reforms crystals in a new pattern as the solvent cools and/or evaporates.

Question 30

Crystallization

Answer 30

-an Equilibrium Process
-Initially, as solute is added to solvent, dissociation occurs at a high rate.
-Once there are enough solute molecules that can interact with each other in solution, the saturation limit, crystallization occurs.
-Equilibrium is set up when the rate of dissolving and crystallization become equal, i.e. the rate of crystal reformation is the same rate of crystal dissolution.
-For some solutes that are slightly soluble in a given solvent, only a few particles will disperse in the solvent compared to the majority of the particles which will remain as a crystal or rapidly crystallize, also forming setting up a system at equilibrium as represented by the reaction equation below.
-Just like any other equilibrium process there is a favored direction for the reaction.
-The most energetically stable process will be favored.
-For solutes that are highly soluble, the forward reaction, or dissolution, is most favored (arrow pointed to the right)
-solutes with low solubilities will favor the reverse direction of recrystallization (arrow pointed to the left).

Question 31

dissolution/crystallization

Answer 31

-Factors that affect solubility will also affect the dissolution/crystallization of a saturated solution at equilibrium. -Slightly soluble solutes readily form saturated solutions, and thus rapidly form equilibrium systems
-Solutes with higher solubility will need higher concentrations to form saturated solutions than those with lower solubility.
-For any saturated solution, adding more solute will shift the equilibrium to the left since the solution is already past its solubility point and no further solute can dissolve.
-Removing some of the solvent via evaporation will increase crystallization as well, since in effect the solute is concentrated and particles will have more contact with each other without the interference of solvent particles hindering their interactions.
-Diluting the solution will shift the equilibrium to the right since more solvent allows for additional dissolution essentially reducing the solute concentration.
-heating a solution will initially aid in dissolving more solute for substances since solubility increases with increasing temperature for solid solutes.
-solutes that dissolve endothermically will absorb energy from their surroundings upon dissolving, and cooling the solution will cause the equilibrium to shift towards recrystallization.
-However, if dissolution of a solute is an exothermic process that produces energy, adding heat will slow down the rate of dissolution and increase the rate of crystallization

Question 32

Saturation unit

Answer 32

G solute /100mL solvent

Question 33

Concentration calculation table

Answer 33

Question 34

Molarity (M)

Answer 34

(Mol) solute/ L solution

-The number of moles of solute in a given solution of a specific concentration can be determined using molarity as a conversion factor
(# mol = M x L solution).

-Using the periodic table, the molar mass of any pure substance can be calculated by adding up the atomic masses of all of the atoms present expressed in the units g/mol.

Note: when calculating molar masses, use 4 sig figs when doing molar mass calculations

Question 35

m/m% (usually for solid solutions)

Answer 35

(g solute/ g solution) x 100
Conversión factor:
g solute/100 g solution

Question 36

m/v % concentration (usually for liquid solutions with solid solutes)

Answer 36

g solute / mL solution x 100
Conversion factor:
g solute/ 100 mL solution

Question 37

v/v % concentration

Answer 37

volume solute /volume solution x 100
Conversion factor:
Volume solute/100 mL solution

Question 38

Dilution calculation

Answer 38

changes in the solution concentration can be determined by comparing the product of the initial concentration and volume to the product of the final concentration and volume using the following equation:

C1V1 = C2V2

CV = moles of solute (constant)

Since the amount of solute remains constant during dilution, changes in the solution concentration can be determined by comparing the product of the initial concentration and volume to the product of the final concentration and volume using the following equation:

Question 39

Tips for dilution calculations:

Answer 39

• First determine the given values representing the initial and final states.
• Rearrange the equation to solve for the needed value, and solve by putting the values into the equation
• Check to ensure your answer makes sense
• If solving for the final concentration, the value should be less than the initial concentration, and vice versa (C1 > C2)
◦ o If solving final volume, the value should be greater than the initial volume, and vice versa (V1 < V2)

Question 40

Four colligative properties arise when solutions form.

Answer 40

1. Vapor pressure depression (lowering)
   
   2. Boiling point elevation
   3. Freezing point depression
   4. Osmotic pressure (usually for aqueous solutions)

A molecular unit of a covalent compound is only one molecule such as glucose. At the molar level, one mole of NaCl dissolves forming 2 moles (1.2 x 1024 particles) of ions in solution; likewise, 3 moles (1.8 x 1024 particles) of ions are formed by one mole of CaCl2. Whereby one mole of glucose will dissolve into one mole of glucose (6.02 x 1023 particles) molecules. The greater the concentration of particles in solution, the greater the effect on colligative properties.

Question 41

Electrolytes

Answer 41

Produce Ions in Solution

Question 42

equivalent (Eq)

Answer 42

-The concentration of electrolyte or electronic charge in solution is given by the unit equivalents per liter (Eq/L).
-An equivalent (Eq) is equal to one mole of electronic charge, whether positive or negative.
-An ion with a +1 or -1 charge is 1 Eq. -An ion with +2 or -2 charge is 2 Eq; -likewise an ion with a 3+ or 3- charge is 3 Eq.
-As shown above one mole of NaCl produces 2 moles of ions (a 1+ ion and a 1- ion).
-Since each ion has a 1 charge, there are 2 Eq per mole of NaCl.

Question 43

Vapor Pressure and BP

Answer 43

-The addition of solutes to a pure solvent causes vapor pressure to decrease and boiling point to increase.
-the presence of solute particles also prevents solvent molecules from forming the solvent-solvent interactions necessary to form solid crystals.
-Thus, more energy must be removed from a solution.
-In other words, a lower temperature is required in order for the solvent to freeze, hence a lower freezing point or freezing decreases

Question 44

Collegiative properties

Answer 44

Depends on molality
m= Moles of solute/ kg solvent

Question 45

Osmosis

Answer 45

-net movement, or diffusion, of solvent molecules (mainly water in aqueous solutions) across a semipermeable (selective) membrane
-The pressure that must be applied to the membrane to prevent the spontaneous flow of water is equal to the osmotic pressure of the solution
-The side of the membrane with the highest solute concentration has the higher osmotic pressure.
-If both sides have equal osmotic pressure then the solute concentrations are equal on both sides of the semipermeable membrane.

Question 46

Cremation

Answer 46

Shrinkage of red blood cells in a hypertonic solution

Question 47

Plasmolyzed

Answer 47

Plants become plasmolyzed when placed in hypertonic solutions

Question 48

Hemolysis

Answer 48

term for the bursting of red blood cells when placed in hypotonic solutions

Question 49

Isotonic

Answer 49

-Isotonic solutions have the same concentration of solutes, and osmotic pressures, as the solution within cells. -Red blood cells placed in an isotonic solution maintain their normal shape as water flows into and out of the cell at the same rate
-Plant cells in an isotonic solution are said to be flaccid

Question 50

Reverse osmosis

Answer 50

-purification of drinking water
-involves the forcing of water across a semipermeable membrane against the solute concentration allowing for the separation of solutes such as ions, large molecules, and microorganisms from pure water.
-Water is forced to move towards the solution with little to no solutes dissolved.
-The result is water with very little to no dissolved solids depending on the size of pores used in the membrane.
-A membrane permeable to small solute particles and not large ones can separate solutes in solution by the principle of dialysis or the diffusion solutes across a semipermeable membrane such as dialysis tubing
-particles smaller than the membrane pore size can cross the membrane while others are too large to fit through the pores.

Question 51

Non-polar solvents and solutes

Answer 51

-interact with each other through numerous London dispersion forces between individual molecules so that instantaneous and temporary dipoles in the solute and solvent molecules align themselves to maximize and maintain the short-lived opposite attractions forming the solution
-Organic compounds containing only carbon and hydrogen atoms are non-polar and are only soluble in non-polar solvents such as hexane (C6H14) and benzene (C6H6).

Question 52

Henrys Law

Answer 52

-the solubility of a gas in a liquid solvent is directly proportional to the partial pressure of the gas above the solvent liquid.
-The partial pressure of the gas is essentially the concentration of a gas. -The higher the partial pressure, the more a gas will dissolve in a solvent at a given temperature.
-Decreasing the pressure of a gas will decrease its solubility.
-If more than one gas is dissolved in solution, increasing the partial pressure of one gas will only increase its solubility, not the solubility of the other gases.
-Increasing the partial pressure of one gas will actually decrease the solubility of another gas in solution since they will be “competing” for space in the solvent.