Chemistry midterm 2: Solutions and Colloids Flashcards
What is a solution
a uniform, homogeneous mixture where solute is present as individual atoms, ions or small molecules
An alloy is
solid solution of one metal dissolved in another
What is a solute
the least amount component in solution comprised of substances within a solution
What is a solvent
the most abundant component in a solution which determines the state of the solution
What is solubility
the maximum amount of solute that dissolves in a fixed quantity of solvent at a given temperature
What are some characteristics of solutions
- They are homogeneous; after a solution is mixed, it has the same composition at all points throughout (its composition is uniform)
- The physical state of a solution—solid, liquid, or gas—is typically the same as that of the solvent
- The components of a solution are dispersed on a molecular scale; they consist of a mixture of separated
solute particles (molecules, atoms, and/or ions) each closely surrounded by solvent species - The dissolved solute in a solution will not settle out or separate from the solvent
- The composition of a solution, or the concentrations of its components, can be varied continuously (within limits determined by the solubility of the components
The formation of a solution is an example of what type of process
A spontaneous process. a process that occurs under specified conditions without the requirement of energy from some external source
What are two criteria that favour a spontaneous formation of a solution
- a decrease in the internal energy of the system (an exothermic change)
- an increased dispersal of matter in the system (which indicates an increase in the entropy of the system
What is an ideal solution
- When the strengths of the intermolecular forces of attraction between solute and solvent species in a solution
are no different than those present in the separated components, the solution is formed with no accompanying
energy change - A mixture of ideal gases (or gases such as helium
and argon, which closely approach ideal behavior) is an example of an ideal solution, since the entities
comprising these gases experience no significant intermolecular attractions.
What type of attraction plays an important part in the dissolution of ionic compounds in water
ion-dipole attraction
What happens when ionic compounds dissolute in water
When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the
solution because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them. This process represents a physical change known as dissociation
What happens when KCl is added to water
Ion-dipole forces attract the positive (hydrogen) end of the polar water molecules to the negative chloride ions at the surface of the solid, and they attract the negative (oxygen) ends to the positive potassium ions. The water molecules surround individual K+ and Cl− ions, reducing the strong interionic forces that bind the ions together and letting them
move off into solution as solvated ion
What are miscible fluids
dissolve in all proportions
What are immiscible fluids
do not mix; form layers
What is a saturated solution
- When a solute’s concentration is equal to its solubility
- Suppose we place some solute in a container of solvent. Some solute dissolves, solution concentration increases for some time. Eventually, the concentration remains constant
- At this point the solution is said to be saturated. No more solute will go into solution
- rate of dissolution is equal to the rate of deposition
What is an unsaturated solution
- If the solute’s concentration is less than its solubility
- rate of dissolution is greater than the rate of deposition; more solute is capable of dissolving
What is a supersaturated solution?
- there is more solute dissolved than the equilibrium amount, the solution is unstable and solid will spontaneously precipitate out
When is dynamic equilibrium reached
- when solute molecules dissolve and recrystallize at the same rate.
What happens in solutions of gases and liquids
The solubility of a gas in a liquid is affected by the intermolecular attractive forces between solute and solvent species. Unlike solid and liquid solutes, however, there is no solute-solute intermolecular attraction to overcome when a gaseous solute dissolves in a liquid solvent since the atoms or molecules comprising a gas are far separated and experience negligible interactions. Consequently, solute solvent interactions are the sole energetic factor affecting solubility
The solubility of most solids increases with
temperature (some exceptions).
The solubility of gases increases with
decrease in temperature (inverse relationship), and pressure increase
What is recrystallization
purification technique that slowly cools a saturated solution to form pure crystals of the solute. Impurities are unsaturated and do not crystallize.
What is fractional crystallization
The separation of a mixture of substances into pure components on the basis of their differing solubilities.
Pure A has only A-A interactions, pure B has only B-B interactions, what will the solution have
Solution of A and B has A-A, B-B and A-B interactions
Substances that exhibit similar types of intermolecular
force will
dissolve in each other: “like dissolves in like.”
non-polar molecules are soluble in
non-polar solvents
Polar molecules are soluble in
polar substances
Ionic compounds are soluble in
Polar solvents
Which particles oppose solubility
Charge density and delta H(solute): high charge density opposed solubility
Which particles tend to be soluble
Low charge density salts
How can the temperature dependence of solubility can be exploited to prepare supersaturated solutions of certain
compounds
A solution may be saturated with the compound at an elevated temperature (where the solute is
more soluble) and subsequently cooled to a lower temperature without precipitating the solute. The resultant
solution contains solute at a concentration greater than its equilibrium solubility at the lower temperature (i.e.,
it is supersaturated) and is relatively stable. Precipitation of the excess solute can be initiated by adding a seed
crystal (see the video in the Link to Learning earlier in this module) or by mechanically agitating the solution
What prevents oil from dissolving in water
strong water-water interactions
When ionic solutions dissolve, the ion-ion force changes to
ion-dipole force
How do ion-dipole forces orient a molecule
Ion-dipole forces orient water molecules around an ion. In
the innermost hydration or solvation shell here, six water
molecules surround the cation octahedrally.
Dissolved ions and their solvated shell of water molecules
can move as intact entities when an electric field is applied
What are electrolytes
The solutions formed from ionic species are conductors of electricity
What is solavation
the process of surrounding a particle with solvent particles. In water, solvation is called hydration
The hydration of an ion is always
exothermic because ion-dipole forces are very strong
High charges and small ionic radius contribute to
strong heats of hydration. Heats of hydration decrease down a group and increase across a group
high charges and small ionic radii also result in
High lattice energies
When a solution forms, solute-solute attractions and solvent-solvent attractions are replaced by
Solute-solvent attractions. This can only occur if the forces within the solute and solvent are similar to the forces that replace them.
What are driving forces of dissolution
- Tendency towards greater disorder
- Minimizing potential energy (enthalpy), minimizing attractive forces
Gas solubility can be characterized by which law
Henry’s Law. Gases are more soluble in water as
pressure increases
Descibe suba driving and “The Narcs”
- Deep-sea divers breathe high pressure air underwater
- Dissolved Nitrogen at depths of 25 – 40 m caused intoxication
- This condition is often called “The Narcs” or “”Rapture of the Deep”
Describe solubility of CO2 in carbonated drinks
- Solubility of CO2 in water is high under high pressure
- Opening a bottle relieves the pressure, solubility decreases.
- CO2 evaporates from solution as fizz
Describe scuba diving and “The Bends”
- Deep-sea divers breathe high pressure air underwater
- Excess N2 dissolves in the blood
- A rapid return to the surface causes N2 to diffuse out of the blood
- This painful and often dangerous condition is called “the Bends”
What are colligative properties
There are a few solution properties, however, that depend
only upon the total concentration of solute species, regardless of their identities. These colligative properties
include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.
What are colligative properties
properties that depend on the relative amounts of solute and solvent and are independent of the chemical identity of the solute
What are electrolytes
separate into ions when it dissolves (ionic compounds)
What are non-electrolytes
does not dissociate to form ions (molecules)
What are extensive properties
depend on the quantity of matter (in atoms), volume, and mass whereas intensive properties are independent of the quantity of matter, density, and temperature. Colligative is a new third category
The French scientist Francois-Marie Raoult, discovered
that, at any temperature, the vapor pressure of a solvent is proportional to its mole fraction in a solution
What is Raoult’s law
The partial pressure exerted by any component of an ideal solution is equal to the vapor pressure of the pure component multiplied by its mole fraction in the solution.
According to Raoult’s law, when two volatile liquids A and B are mixed,
- the total vapour pressure is above the mixture is the sum of the vapour pressures of the two components
For a volatile nonelectrolyte, the vapour of the solution
contains
both solute and solvent.
What is fractional distillation
method of separating volatile liquids from one another
Describe process of distillation
- Start by heating the solution to its boiling point
- Collect the vapour which is richer in the more volatile compound
- Cool and condense the vapour to a liquid
- Repeat until desired purity is reached
What are Azeotropes
liquid mixtures that we are unable to separate by distillation
What is boiling point elevation
The increase in boiling point observed when nonvolatile solute is dissolved in a solvent, ΔTb, is
called boiling point elevation and is directly proportional to the molal concentration of solute species
Boiling point elevation constants are characteristic properties that depend on the identity of the
Solvent
What is the freezing point depression
The decrease in freezing point of a dilute solution compared to that of the pure solvent, ΔTf, is called the
freezing point depression and is directly proportional to the molal concentration of the solute
What is activity
the “effective concentration” of a species, as measured by colligative properties
What is osmosis
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
Osmotic pressure is
the pressure that must be applied to prevent the net flow of solvent
Describe osmotic pressure and red blood cells
- A red blood cell in an isotonic solution has its normal
shape. - A hypotonic solution has a lower concentration of particles than the cell. A cell in a hypotonic solution absorbs water and swells until it bursts
- A hypertonic solution has a higher concentration of
dissolved particles than the cell. If a cell is placed in
a hypertonic solution, water moves out of the cell,
causing it to shrink
What is isotonic solution
of equal osmotic pressure
What is a hypertonic solution
of greater osmotic pressure
A strong electrolyte dissociates
completely to form ions. Each mole of solute gives more than 1 mol of dissolved particles
The formula of the compound indicates
the expected number of particles in solution
The van’t Hoff factor takes into account
the dissociation of a strong electrolyte to predict the effect on the solution
What is reverse Osmosis
- Sea water can be desalinated by “reverse osmosis,”
- P applied to hypertonic side: Forces pure water through membrane, Need P must be > Π
For colloids, the particulate component typically present in a relatively minor amount is called
Dispersed phase
For colloids, the substance or solution throughout which the particulate is dispersed is called the
Dispersion medium
Colloids may involve virtually any combination of
physical states (gas in liquid, liquid in solid, solid in gas, etc.)
Particles of colloidal size are formed by two methods, they are:
- Dispersion methods: breaking down larger particles. For example, paint pigments are produced by dispersing large particles by grinding in special mills.
- Condensation methods: growth from smaller units, such as molecules or ions. For example, clouds form when water molecules condense and form very small droplets
How can an emulsion be prepared
by shaking together or blending two immiscible liquids. This breaks one liquid into droplets of colloidal size, which then disperse throughout the other liquid. Oil spills in the ocean may be difficult to clean up, partly because wave action can cause the oil and water to form an emulsion
What is an emulsifying agent
a substance that inhibits the coalescence of the dispersed liquid. For example, a little soap will stabilize an emulsion of kerosene in water.
