General Chemistry- Solutions Flashcards
What are solutions?
Homogeneous (the same throughout) mixtures of two or more substances that combine to form a single phase, usually the liquid phase.
What are mixtures?
Gases “dissolved” into other gases can be thought as solutions, but are more properly defined as mixtures because gas molecules do not interact all that much chemically.
Can all solution be considered mixtures? Can all mixtures be considered solutions?
All solution are considered mixtures, but not all mixtures are considered solutions.
What do solutions consist of?
A solute and solvent
What is a solute?
Something dissolved or dispersed in a solvent.
NaCl, NH3, C6H12O6, CO2
What is a solvent?
The component of the solution that remains in the same phase after mixing. If the two substances are already in the same phase, 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 context is considered the solvent.
What do solute molecules do in a solvant?
Move 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.
What is solvation?
The electrostatic interaction between solute and solvent molecules.
What is another name for solvation?
Dissolution, and when in water Hydration
What is involved in solvation?
Solvation involves breaking intermolecular interactions between solute molecules and between solvent molecules and forming new intermolecular interactions between solute and solvent molecules together.
When is a solvation exothermic?
When the new interactions are stronger than the original ones
What are examples of exothermic processes?
The dissolution of gases into liquids, such as CO2 into water, because the only significant interactions that must be broken are those between water molecules.
What does Le Chatelier’s principle tell us?
That lowering the temperature of a liquid favors solubility of a gas in the liquid.
When is a solution endothermic?
When the new interactions are weaker than the original ones
Most dissolutions are exothermic or endothermic?
Endothermic
What are examples of endothermic dissolutions?
Dissolving ammonium nitrate or sugar into water
What must be added to an endothermic dissolution? Why?
Energy must be added because the new interactions between the solute and solvent are weaker than the original interactions between the solute molecules.
What happens when the overall strength of a endothermic solution is equal to the overall strength of the original interaction?
The overall 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 contributes to the sponteneity of dissolution?
Enthalpy change.
Gibbs free energy
What always increases upon dissolution at constant pressure and temperature?
Entropy always increases
Sponteneous processes in dissolution are associated with what in regards to free energy? Nonspontaneous?
Decrease in free energy
Nonspontaneous process with increased free energy
Is the formation of ion-dipole interactions exothermic or endothermic?
Exothermic
Why is the dissolution of table salt in water endothermic?
The magnitude is slightly less than the energy required to break the ionic bonds and hydrogen bonds. As a result the overall dissolution of table salt inot water is endothermic and favored at high temperatures.
What is entropy?
The degree to which energy is dispersed throughout a system or the amount of energy distributed from the system to the surroundings at a given temperature.
What is another way to understand entropy?
The measure of molecular disorder, or the number of energy microstates available to a system at a given temperature.
What does it mean when you say ions have a greater number of energy microstates?
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).
If a solid dissolves in a liquid forming a liquid, what happens to the solid’s entropy and what happens to the liquids entropy?
A solid’s energy is more distributed and the entropy increases
Liquid becomes more restricted in its movements, microstates decrease and entropy decrease.
How do you determine the overall entropy of a solution?
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.
What is solubility?
The maximum amout of that substance that can be dissolved in a particular solvent at a given temperature.
When do we say a solution is saturated?
When the maximum amount of solute has been added, the solution is saturated. If more solute is added, it will not dissolve
What is dilute?
A solution in which the proportion of a solute to solvent is small.
What is concentrated?
The proportion of solute to solvent is large
When are dilute and/or concentrated solutions unsaturated?
If the maximum equilibrium concentration has not yet been reached.
The soluability of substance in different solvants is a function of what?
Thermodynamics.
What happens when the change in Gibbs free energy for a dissolution reaction is negative at a given temperature? What about positive?
The process will be spontaneous and the solute is soluble, if negative.
If positve, The process is nonspontaneous and the solute insoluble.
How do you consider a solute soluable?
If they have a molar solubility above 0.1 M in solution
What are sparingly soluble salts/
Those solutes that dissolve minimally in the solvent (molar solubility under 0.1 M)
What is the most common type of solution?
The aqueous solution
What is an aqueous solution?
The solvent is water
How is the aqueous state denoted?
The symbol (aq)
What is hydration?
The process through which dissolution occurs
In some acid solutions, what complex may form when mixed with water?
Hydronium ion (H30+)
Is H+ ever found alone in solution? Why?
No, because a free proton is difficult to isolate
Why does the MCAT focus on Aqueous solution?
Aqueous solutions are so common and so important to biological systems
What are the seven solubility rules of aqueous solutions?
- All sals containing ammonium (NH4+) and alkali metal (group 1) cations are water-soluble.
- All salts contain nitrate (NO3-) and acetate (CH3COO-) anions are water soluble.
- Halides (Cl-, Br-, I-), excluding fluorides, are water-soluble, with the exception of those formed with Ag+, Pb 2+ and Hg2 2+
- All salts of the sulfacte ion (SO4 2-) are water soluble, with the exceptions of those formed with Ca 2+, Sr 2+, Ba 2+, and Pb 2+
- All metal oxides are insoluble, with the exception of those formed with alkali metals, ammonium, and CaO, SrO, and BaO, all of which hydrolyze to form solutions of the corresponding metal hydroxides.
- All hydroxides are insoluble, with the exception of those formed with alkali metals, ammonium, and Ca 2+, Sr 2+, Ba 2+.
- All carbonates (CO3 2-), phosphates (PO4 3-), sulfides (S 2-), and sulfites (SO3 2-) are insoluble, with the exception of those formed with the alkali metals and ammonium.
What are the two absolute rules of solubility in aqueous solutions you should know on the MCAT?
All salts of Group 1 metals, and all nitrate salts are soluble.
What are usually used as counter ions?
Sodium and nitrate ions are generally used as counterions to what is actually chemically important
When is the only time you should worry about nitrate ion concentration as a chemically reacting species? Otherwise just focus on what?
In an oxidation-reduction reaction, for the nitrates ion to function, weakly, as a oxidizing agent.
Otherwise just focus on the cation as the chemically reacting species.
What is a complex ion?
A molecule in which a cation is bonded to at least one electron pair donor (which could include the water molecule).
What is another name for complex ion?
Coordination compound.
What are ligands?
The electron pair donor molecules.
What is an example of a complexation reaction?
The tetraaquadioxouranyl cation, which has water (aqua-) and oxygen (oxo-) ligands.
How are complexes held together?
Coordinate covalent bonds
What are coordinate covalent bonds?
An electron pair donor (a Lewis base) and an electron pair acceptor (a Lewis acid) form a very stable Lewis acid-base adducts.
What biologically uses complex ion bonding?
Many active sites of proteins utilize complex ion binding and transition metal complexes to carry out their function.
What is an example of complex ion binding biologically?
The iron cation in hemoglobin, which can carry oxygen carbon dioxide, and carbon monixde as ligands
What else contains complexes of transition metals?
Many coenzymes (vitamins) and cofactors also contain complexes of transition metals.
What is an example of a coenzymes/cofactor?
Cobalamin (vitamin B12)
What does the presence of a trantion metal allow in coenzymes and cofactors?
Bind other ligands or assist with electron transfer.
What is chelation?
In some complexes, the central cation can be bonded to the same ligand in multiple places.