Chemistry 111

experiment 2:

 

define spectroscopy

the study of the interaction of electromagnetic radiation with matter

experiment 2:

 

difference between a line and continuous spectrum, give an example of each

continuous: the emitted radiation contains all frequencies within a region of the electromagnetic spectrum

(light from lightbulb)

line: produced by excited atoms in the gas phase and contain only certain frequencies, all other frequencies being absent

(chemical elements- unique)

experiment 2:

 

what kind of energy transitions were observed in this experiment?

electronic transitions

experiment 2:

 

define “white light” and the range (in nm) that it covers

small band of electromagnetic spectrum ranging from 400-800 nm that is made up of colors of the rainbow that is visible to humans

experiment 2:

 

list the colors of the spectrum from highest to lowest frequency

violet, blue, green, yellow, orange, red

experiment 2:

 

what is the purpose of this “discharge tube” set up?

gas molecules become excited and emit light when turned on, purpose is to measure wavelength using calibrated spectroscope and determining wavelength using calibration equation, then comparing to actual values to determine percent error

experiment 2:

 

explain the effect of the spectrum

(a) changing slit width

(b) distance from source of light

(a) chances width of the spectral lines viewed through spectroscope (thinner slit, thinner line), more precise measures

(b) changes the intensity of the light (closer=more intense)

experiment 2:

 

how you calibrated your microscope

1. attach graph paper and number, view fluorescent light for 3 most prominent lines (Hg)

2. record location of prominent lines according to numbers placed on graph

3. graph, one axis being number on graph section, the other being actual wavelength

4. connect dots to form a line, then find equation of the line

experiment 2:
experiment 2:
experiment 2:

experiment 3:

 

explain the complementary nature of absorbed/observed colors

the color being observed can be seen because the complementary colors are being absorbed.

the complement is absorbed because there are electronic energy level transitions in the molecules that correspond to the photon energy of the compliment.

experiment 3:

 

why will a substance absorb visible light?

the radiation possesses the energy needed to move an electron from its lowest energy stated to some excited state

(low energy state–> higher energy state)

experiment 3:

 

describe technique of colorimetry

a set of solutions of known concentrations of some light absorbing substance are placed in a series of containers. an unknown concentration solution is compared with the calibration set, either by eye or with aid of instrument. Matching to unknown to a known determines unknown concentration

experiment 3:

what process removes the energy from excited food dye molecules in aqueous solution?

energy is removed by solvent molecules bumping billions of times/second against the excited food molecules. there is a small increase in the thermal energy of the solvent.

(do not emit radiation)

experiment 3:

 

what is the dilution equation?

Ci x Vi = Cf x Vi

c=concentration

v=volume

i=initial

f=final

experiment 3:

 

what is beer lambert’s law?

T=10(exp)-abc

A=abc

;

a=constant (depends on substance absorbing light)

b=path length of light sample

c=concentration of absorbing substance in the solution

;

*governs absorption of light by solutions

;

b increases, c decreases

c increases, b decreases

experiment 3:

;

what is intensity related to?

related to path length and concentration

experiment 4:

;

-reasons why aluminum is expensive to produce

-two uses for the slum compound that you synthesized

-1) high grade bauxite deposits occur outside US

2) Hall-Herlout process is extremely energy intensive

-1) paper making

2) fire extinguishing compounds

experiment 4:

;

difference between corrosion of iron and the corrosion of aluminum

aluminum surface reacts with oxygen in the air to form a tenacious, thin film that effectively stops further corrosion, while iron does not

experiment 4:

;

what is an “alum”?

a generic name for a variety of aluminum compounds that are composed of aluminum sulfate and a group 1A metal sulfate or ammonium sulfate

experiment 4:

;

H2SO4 is added to one of the scratched up areas of an aluminum can bubbles are observed. Write a reaction equation to explain this observation.

Al + H2SO4 –> Al2(SO4)3 + H2

experiment 4:

 

write an equation which explains why carbonated beverages are acidic?

CO3 + H2O –> HCO3 + OH

experiment 4:

 

what is the equation for theoretical yield?

absolute value of actual/theoretical x 100%

experiment 4:

 

tested for presence of SO4, K, Al, H2O

SO4- present because it is insoluble with Barium and forms a precipitate (BaSO4)

K- flame test

(flame was purple)

H2O- expanded when heated because water was breaking up

Al- aluminum hydroxide was formed when OH was added to Aluminum

experiment 4:

 

what two things does the melting point of alum tell you?

identity of the material

purity of the material (compare melting point found to actual melting point)

experiment 4:

 

reaction of crystal draino

2Al(s) + 2KOH(aq) + 6H2O(l) –> 2KAl(OH)4(aq) + 3H2

experiment 7:

 

explain the “like dissolves like” principle

 

specific example

 

like intermolecular forces dissolve with like intermolecule forces

 

polar molecules dissolve in polar solvents

nonpolar molecules dissolve in nonpolar solvents

 

 

experiment 7:

 

“like dissolves like” to explain solubility experiments you did with ehtanol, pentanol, kerosene, and water

-knowing that water is polar (by structure), by adding kerosene to water, it runs directly off, showing that it is nonpolar.

-ethanol is polar because it would not mix with kerosene which was found to be nonpolar

-water is polar by structure

-pentanol is partially polar because it will separate in water, but not fully dissolve

experiment 8:

 

whats one advantage of BTB over red cabbage?

BTB is man-made, so that whenever it is needed it can be produced. Also, red cabbage, since it is natural, can be infected by pesticides or other chemicals while BTB is consistent.

experiment 8:

 

explain the difference between a “serial” titration and a “single well” titration (advantage of each?

serial: titration that takes in a 1×12 well strip so that each step of titration can be seen

 

single well: titration that takes place in one well, it is just as efficient and quicker

experiment 8:

 

net ionic equation or HCl and NaCl, observed at the endpoint?

 

OH- + H –> H2O(l)

 

color changes from yellow to dark blue, in well 6 equivalence point occurs

experiment 8:

 

what is back titration?

what is the advantage?

-adding excess amounts of HCl (acid) to completely dissolve calcium carbonate, the titrating the uncreacted acid with a soluble base to the standard solution

 

faster.

experiment 10:

 

what is meant by hardness of water?

 

problems caused by hard water (2)

determined by the presence of the dissolved divalent cations, specifically Ca2+ and Mg2+

 

-soap anion produces insoluble, greasy scum

-metal corrosion/structural weakness

experiment 10:

 

why is a buffer necessary for EDTA?

why does each sample need to be “spiked” with MgEDTA?

-make sure that there is enough magnesium to start the reaction

experiment 10:

 

experiment 10:

 

explain what is happening when water is “softened” by adding either washing soda, or an ion exchange resin?

divalent cations are replaced with monovalent cations.

 

removes magnesium/calcium

experiment 10:

 

how is atomic absorption carried out? and the principles behind how it works?

determines what metals are dissolved or suspended in a solution

-there is monochromatic light that is proportional to delta E of an element

-water tested is aspirated into fine aersol which is introduced to flame

-everything is atomized and light will only be absorbed if energy levels match

-monochrometer allows only certain wavelength to pass through

-detector measures decrease in initial signal which is proportional to concentration

experiment 10:

 

what is “beer-lambert law” and what is its significance in AA?

It=Io(10(exp)-abc)

 

used to calculate the unknown metal concentration in the sample

 

Io is intensity of initial light source

experiment 10:

 

what is the purpose of the “standards”in AA analysis?

check accuracy and reproducibility of the instrument

experiment: 10

 

what is the problem with analyzing a sample whose absorbance exceeds 1 absorbance unit?

what is done in this experiment to compensate for this problem?

if the sample exceeds one absorbance unit, there is little light transmitted for the PMT to detect. In this case, solution should be diluted
experiment 10:

experiment 10:

 

why is water hardness measured by AA less than hardness determined by EDTA titration?

AA only measures Calcium and Magnesium, while EDTA titration tests for all divalent cations which would in turn make the amount larger.

experiment 7:

 

define acid/base reaction

formation covalent, neutral water molecules from hydrated hydrogen

experiment 7:

 

define precipitation reaction

produces insoluble compound

experiment 7:

 

define complexation reaction.

one or more covalent bonds produced during formation of product

experiment 7:

 

define oxidation reaction.

electrons are transferred