Solutions

Question 1

solute

Answer 1

things being dissolved

Question 2

solvent

Answer 2

material doing dissolving

Question 3

methods of measuring solubility

Answer 3

3 methods

• mass per unit volume of solvent
  10 g per 100 mL
• molality
  molality, m = moles of solute/ kiliograms of solent

0.08 moles/0.1 kg = 0.8 molal

• molarity, M
  moles of solvent / liters of solution

Question 4

How do we prepare a specific molarity?

Answer 4

we add solute to a volume of solvent less than target volume until molarity reached

doesnt create excess solution

Question 5

when should you measure volume in creating molarity solution

Answer 5

measuring volume after dissolving

Question 6

for aqueous solutions, molarity and molality are nearly the same

Answer 6

bc 1 L water = 1 kg

for non aqueous or concentrated solvents they are very different

Question 7

molar solubility

Answer 7

molarity of solution when saturated (as much solute dissolved as possible)

Question 8

solubility product

Answer 8

like an equilibrium constant big Ksp
solids and pure liquids dont appear in eq constants so only numerator is kept

Question 9

What is Ksp and how to find Ksp

Answer 9

Ksp is the special equilibrium constant which quantifies solubility

Use ksp equation using only products (solution when saturated)

large ksp means very soluble

Question 10

super saturated

Answer 10

more is dissolved than should be able to

makes Ksp < IP

Precipitation occurs

Question 11

find ion product IP is a specific description in unsaturated conditions

Answer 11

same process as Ksp
compare ksp to IP

IP < Ksp
when IP = KSP its saturated
reached equilibrium

Question 12

which ion precipitated?

Answer 12

compare Ksp
low Ksp means precipitate
(IP > Ksp)

Question 13

common ion effect

Answer 13

the presence of an ion in solution will decrease solubility of compounds containing that ion

Question 14

what is ion product

Answer 14

it determines if a precipitate forms

IP > Ksp ==> precpitates

Question 15

how to manipulate base solution to dissolve?

Answer 15

add an acid

Question 16

Answer 16

kb is the molal boiling point elevation constant for solutions in a given solvent

Question 17

what are the properties of boiling point

Answer 17

Question 18

what kind of reaction is H+ + OH- –> H20

Answer 18

neutralization and combination

A neutralization reaction is when an acid and a base react to form water and a salt and involves the combination of H+ ions and OH- ions to generate water. The neutralization of a strong acid and strong base has a pH equal to 7.

Question 19

How do you find the maximum amount of a product that can be produced from a reaction?

Answer 19

1. stiochiometry of reaction and starting amount of each reactant

find the net reaction by canceling terms

2. find the amounts of each reactant

100 mL x mole concentrations

3. reaction only proceeds if all reactants are present, the limiting reagent is what stops the reaction
4. the reagent that has the least number of moles is likely the limiting reagent because you solve this by taking # moles of each reactant / its stochiometric coeffcient
5. 0.006 moles for I- which maxes max of 0.03 moles I2. 0.03*250g = 0.750 g of I2

Question 20

reaction rate vs reaction constant

Answer 20

The reaction rate, also known as rate law, is directly related to the reaction constant. But unlike the rate constant, reaction rate also depends on the concentration of the reactants.

Question 21

What are solutions?

Answer 21

**Solutions are homogeneous (the same throughout) mixtures of two or more substances that combine to form a single phase, usually the liquid phase.
**
The MCAT will focus almost exclusively on solids dissolved into aqueous solutions, but it’s important to remember that solutions can be formed from different combinations of the three phases of matter. For example, gases can be dissolved in liquids (carbonating soda); liquids can be dissolved in other liquids (ethanol in water); solids can even be dissolved in other solids (metal alloys). Incidentally, gases “dissolved” into other gases can be thought of as solutions, but are more properly defined only as mixtures because gas molecules do not interact all that much chemical

Question 22

As a point of clarification: all solutions are considered mixtures, but —– mixtures are considered solutions.

Answer 22

As a point of clarification: all solutions are considered mixtures, but not alll mixtures are considered solutions.

Question 23

What is a solute and a solution?

Answer 23

A solution consists of a solute (such as NaCl, NH3, C6H12O6, or CO2) dissolved (dispersed) in a solvent (such as H2O, benzene, or ethanol). The solvent is the component of the solution that remains in the same phase after mixing.

1. If the two substances are already in the same phase (for example, a solution of two liquids), the solvent is the component present in greater quantity.
2. If the two same-phase components are in equal proportions in the solution, then the component that is more commonly used as a solvent in other contexts is considered the solvent.

Question 24

How does the solute move?

Answer 24

Solute molecules move about freely in the solvent and interact with it by way of intermolecular forces such as ion–dipole, dipole–dipole, or hydrogen bonding. Dissolved solute molecules are also relatively free to interact with other dissolved molecules of different chemical identities; consequently, chemical reactions occur easily in solution.

Question 25

What is solvation/dissolution?

Answer 25

Solvation is the electrostatic interaction between solute and solvent molecules. This is also known as dissolution, and when water is the solvent, it can be called hydration. Solvation involves breaking intermolecular interactions between solute molecules and between solvent molecules and forming new intermolecular interactions between solute and solvent molecules

Question 26

when is solvation exothermic?

Answer 26

When new interactions are stronger than orginal ones, solvation is exothermic (and favored at low temps)
CO2–> water is exothermic. Co2 has minimal intermolecular interactions so lowering a temp will favor solubility of a gas a liquid

Question 27

When is solvation endothermic?

Answer 27

When the new interactions are weaker than the original ones, solvation is endothermic and the process is favored at high temperatures. Most dissolutions are of this type.

dissolving ammonium nitrate or sugar into water. Because the new interac

Question 28

what happens if the new interactions of a solvation are equal to overall strength of old interactions?

Answer 28

enthalpy change for the dissolution is close to zero. These types of solutions approximate the formation of an ideal solution, for which the enthalpy of dissolution is equal to zero.

Question 29

What does the spontaneity of a dissolution depend on?

Answer 29

• The spontaneity of dissolution is dependent not only on the enthalpy change; solutions may form spontaneously for both endothermic and exothermic dissolutions.
• entropy change that occurs in the process. At constant temperature and pressure, entropy always increases upon dissolution.
• change in Gibbs free energy: spontaneous processes are associated with a decrease in free energy, while nonspontaneous processes are associated with an increase in free energy. Thus, whether or not dissolution will happen spontaneously depends on both the change in enthalpy and the change in entropy for the solute and solvent of the system.

Question 30

How do hydrophollic and hydrophobic interactions demonstrate solubility?

Answer 30

Proteins dissolve in solution with their most hydrophilic amino acids on the outside and hydrophobic amino acids on the inside because this maximizes the increase in entropy during dissolution.

Question 31

how to tell endothermic or exothermic from KJ/mol values (heat)

Answer 31

+ means endothermic and favored at high temperatures
- means exothermic and favored at low temperatures

Question 32

enthalpy vs entropy

Answer 32

Enthalpy is a term used to describe the total heat content of a particular system, while entropy describes the disorderliness of a system.

Question 33

how does entropy apply to the formation of sodium chloride solution?

Answer 33

entropy is the measure of molecular disorder, or the number of energy microstates available to a system at a given temperature. When solid sodium chloride dissolves into water, the rigidly ordered arrangement of the sodium and chloride ions is broken up as the ion–ion interactions are disrupted and new ion–dipole interactions with the water molecules are formed. The ions, freed from their lattice arrangement, have a greater number of energy microstates available to them (in simpler terms, they are freer to move around in different ways), and consequently, their energy is more distributed and their entropy increases.

The water, however, becomes more restricted in its movement because it is now interacting with the ions. The number of energy microstates available to it (that is, the water molecules’ ability to move around in different ways) is reduced, so the entropy of the water decreases. In the end, the increase in the entropy experienced by the dissolved sodium chloride is greater than the decrease in the entropy experienced by the water, so the overall entropy change is positive—energy is, overall, dispersed by the dissolution of sodium chloride in water. Because of the relatively low endothermicity and relatively large positive change in entropy, sodium chloride will spontaneously dissolve in liquid water (ΔG = ΔH – TΔS).

Question 34

what is solubility?

Answer 34

The solubility of a substance is the maximum amount of that substance that can be dissolved in a particular solvent at a given temperature. When this maximum amount of solute has been added, the dissolved solute is in equilibrium with its undissolved state, and we say that the solution is saturated. If more solute is added, it will not dissolve

Question 35

what does it mean when the solution is saturated

Answer 35

if more solute is added it will not dissolve, rather form a precipitate on the bottom of the container

Question 36

are dilute vs concentrated solution still unsaturated?

Answer 36

yes, if the maximum equilibrium concentration (saturation) has not yet been reached.