chem lab 1212
Terms in this set (53)
Where can you find info about each chemical in lab?
The Material Safety Data Sheets located in the chemistry prep room.
What is an erlenmeyer flask?
a general purpose container used for holding or mixing liquids. Some flasks have graduations on them to indicate approximate volume of contents.
what is a filtering flask?
A heavy wall flask designed for use in suction (vacuum) filtration of solutions. Has side hose connection to attach vacuum tubing.
What is a Buchner funnel?
A porous funnel used with filter paper during vacuum filtration.
What is freezing point depression?
It's a colligative property
When you add salt to ice what happens?
Salt lowers the freezing point of the ice.
What do colligative properties depend on?
Only the number and not on the identity of the solute particles in a solution. Examples include freezing point depression, osmotic pressure and boiling point elevation.
What is freezing point?
the temperature at which the solvent in solution and the pure solid solvent have the same vapor pressure. Basically, the solid and liquid are coexisting.
What is m equal to?
delta T_f/ K_f
What happens when a solute is added to the solvent?
the vapor pressure of the solvent changes and causes the vapor pressure of the liquid solvent to be lowered.
Why does solute being added to a liquid solvent weaken intermolecular forces?
Because the solute particles are interfering or standing between the solvent particles.
what is required to make it possible for the solvent particles to reach each other and form the solid?
how is the freezing point of a solvent lowered?
when any solute is dissolved in that solvent. The nature of the solute is not important, only the amount of the solute.
Why can we quantify the freezing point depression?
Because it is proportional to the amount of solute present in a given mass of solvent.
What is the formula of freezing point depression?
∆t_f=t_(f solution)- t_(f solvent)
How do you find ∆t_f?
K_f * m
What is K_f of water?
-1.86 degrees Celsius
Historically, what were the most common and the most difficult natural colors to produce.
Respectively, yellow and purple.
crystal violet dye
Upon reacting with a Lewis base, the dye undergoes structural changes that cause the molecule in solution to convert from a purple color to colorless. It is not a textile dye and is instead used to dye paper; is a component of navy blue and black inks for printing, ball-point pens and ink-jet printers; fertilizers; antifreezes, detergents and leather jackets.
What are dyes?
Aromatic organic compound--contains planar ring systems with alternating double bonds
How do the molecules have color?
The conjugated compound gains chemical stability from the delocalization of electrons in the ring system. The electrons are not associated with a single atom or one covalent bond. Instead, delocalized pi electrons form an orbital cloud that extends over several adjacent atoms.
What is a chromophore?
the part of a molecule responsible for its color; it's a region in the molecule where the energy difference between the two different molecular orbitals falls within the range of the visible spectrum
Why does the color of the dye disappear when a base is added?
When a Lewis base is added to the central carbon in crystal violet, the central atom now has four single bonds. The geometry around the central atom converts from trigonal planar to tetrahedral--does not allow pi bonding. The color disappears because electron delocalization no longer exists over the entire molecule.
What happens to the rate of the reaction as base is added?
What is the slope of the graph of -lnA vs time?
What does it mean for a reaction to be pseudo-first order and how is it different from a first-order reaction?
a reaction that is pseudo-first order is a second-order reaction that has the kinetics rearranged so that it resembles a first-order reaction. Pseudo-first order reactions result if we pick one of the two reactants and make its initial concentration much greater than the concentration of the other reaction. A first order reaction depends ont he ocncentration of only one reactant.
Why is the slope of K_obs vs [OH^-] equal to K_2?
Because its a pseudoorder reaction. There is an excess of OH^- which makes it so that the only concentration effected is the OH^- concentration in the reaction when talking about the K_2 value. When the reaction is put together, the water's K does not effect the k[OH^-] value.
What is Beer-Lambert Law?
Absorbance= molar absorptivity
concentration of the dye
What does chemical kinetics focus on?
What is the reaction rate of a chemical reaction?
It is the change in concentration of a reactant or product per unit time. The molar concentration of reactant will decrease over time and the molar concentration of product will increase.
What is Arrhenius Equation?
k= Ae^-Ea/RT; where R=8.314 J/Kmol; and increase in temperature will lead to a larger k value and a higher reaction rate; A is the frequency factor--a constant that reflects the frequency of collisions with proper orientation; Ea is the difference in energy between the reactants and the transition state--the energy barrier that must be overcome for the reaction to proceed
What is activated carbon?
a form of carbon with a very high surface area; it is processed to have small, low-volume with a very high surface area; make it an effective medium for gas filtration and liquid absorption
exhibits the greatest magnetism of any mineral on Earth; the synthetic form is ferrofluid--consists of nanoscale ferromagnetic particles evenly dispersed in a carrier fluid
What are the desirable properties of ferrofluids?
reactive surfaces, a large surface area to volume ratio, easy separation by applying a magnetic field and a relatively low cost
what is a nanocomposite?
it is a multiphase solid material where one of the phases has a one, two or three dimensions of less than 100 nm
A graph of the complex ion data gives a slope of?
What is the mole ration of Fe^2+ to Fe^3+ ions in the magnetite?
Activated carbon binds to most substances through van der waals or London dispersion forces. Explain why it's effective in absorbing aromatic pollutants such as dyes, but is ineffective in removing most inorganic pollutants such as arsenic and nitrates.
Activated carbon is extremely nonpolar like most organic substances. Thus it is effect because the nonpolar activated carbon attracts the nonpolar aromatic dues. it is ineffective because most inorganic substances are polar.
how is the removal of nitrates by alum (potassium aluminum sulfate) similar to the absorption of organic pollutants by activated carbon?
alum is a flocculant which causes particles to pull together in a clump, then settle. Alum is used up in this process unlike the activated carbon, but similar to alum it pulls the particles together in clumps.
What is a neutralization reaction?
A chemical reaction between an acid and a base to form a salt and water. It may be interpreted as a proton transfer reaction where a proton is transferred from the acid to the base.
In general, what does a larger K_a mean?
It indicates a greater extent of ionization and thus a stronger acid.
What is pH titration?
a common technique to determine the extent of ionization and K_a for a weak acid
What is the equivalence point?
the point of titration where a stoichiometric amount of base has been added; just enough base has been added to completely react with all of the acid present
extent of ionization
[H_3O^+]/ M_A * 100
pH of a buffer solution
ph=pK_a + log ([A^-]/[HA])
What are solubility product constants used for?
Describing saturated solutions of ionic compounds with relatively low solubility.
What is a saturated solution?
in a state of dynamic equilibrium between the dissolved, dissociated, ionic compound and the undissolved solid
What is the common ion effect?
in general, the solubility of an ionic compound is lower in a solution containing a common ion that in pure water.
What is a photovoltaic cell?
a device that converts light energy into electrical energy; they are composed of semiconductors that pass an electrical current through the cell (silicon is the most commonly used material)
What will our nanocrystalline dye sensitized solar cell consist of?
a layer of titanium dioxide that has been stained with a natural dye
Why is a mediator, in this case the iodide ion, needed?
The dye molecule releases electrons when it absorbs light and those electrons must be replaced by a mediator in order for the solar cell to continue producing electricity. In this case, when the iodide ion is converted to triiodide, electrons are released
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