Solutions Flashcards
solute
things being dissolved
solvent
material doing dissolving
methods of measuring solubility
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
How do we prepare a specific molarity?
we add solute to a volume of solvent less than target volume until molarity reached
doesnt create excess solution
when should you measure volume in creating molarity solution
measuring volume after dissolving
for aqueous solutions, molarity and molality are nearly the same
bc 1 L water = 1 kg
for non aqueous or concentrated solvents they are very different
molar solubility
molarity of solution when saturated (as much solute dissolved as possible)
solubility product
like an equilibrium constant big Ksp
solids and pure liquids dont appear in eq constants so only numerator is kept
What is Ksp and how to find Ksp
Ksp is the special equilibrium constant which quantifies solubility
Use ksp equation using only products (solution when saturated)
large ksp means very soluble
super saturated
more is dissolved than should be able to
makes Ksp < IP
Precipitation occurs
find ion product IP is a specific description in unsaturated conditions
same process as Ksp
compare ksp to IP
IP < Ksp
when IP = KSP its saturated
reached equilibrium
which ion precipitated?
compare Ksp
low Ksp means precipitate
(IP > Ksp)
common ion effect
the presence of an ion in solution will decrease solubility of compounds containing that ion
what is ion product
it determines if a precipitate forms
IP > Ksp ==> precpitates
how to manipulate base solution to dissolve?
add an acid
kb is the molal boiling point elevation constant for solutions in a given solvent
what are the properties of boiling point
what kind of reaction is H+ + OH- –> H20
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.
How do you find the maximum amount of a product that can be produced from a reaction?
- stiochiometry of reaction and starting amount of each reactant
find the net reaction by canceling terms
- find the amounts of each reactant
100 mL x mole concentrations
- reaction only proceeds if all reactants are present, the limiting reagent is what stops the reaction
- 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
- 0.006 moles for I- which maxes max of 0.03 moles I2. 0.03*250g = 0.750 g of I2
reaction rate vs reaction constant
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.
What are solutions?
**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
As a point of clarification: all solutions are considered mixtures, but —– mixtures are considered solutions.
As a point of clarification: all solutions are considered mixtures, but not alll mixtures are considered solutions.
What is a solute and a solution?
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.
- 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.
- 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.
How does the solute move?
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.
What is solvation/dissolution?
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
when is solvation exothermic?
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
When is solvation endothermic?
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
what happens if the new interactions of a solvation are equal to overall strength of old interactions?
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.
What does the spontaneity of a dissolution depend on?
- 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.
How do hydrophollic and hydrophobic interactions demonstrate solubility?
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.
how to tell endothermic or exothermic from KJ/mol values (heat)
+ means endothermic and favored at high temperatures
- means exothermic and favored at low temperatures
enthalpy vs entropy
Enthalpy is a term used to describe the total heat content of a particular system, while entropy describes the disorderliness of a system.
how does entropy apply to the formation of sodium chloride solution?
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).
what is solubility?
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
what does it mean when the solution is saturated
if more solute is added it will not dissolve, rather form a precipitate on the bottom of the container
are dilute vs concentrated solution still unsaturated?
yes, if the maximum equilibrium concentration (saturation) has not yet been reached.
