Chem 111 Lab Final Exam
Small Scale Techniques: Be able to calculate a standard deviation by hand for a given set of data. You will not be given the equation for standard deviation.
Standard deviation equation: [(∑(x-x1)^2)/(N-1)]^.5 the average x value is subtracted from the attained x value from the equation N is the total amount of results
Use and Abuse of aluminum: When 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. (If you do this correctly you will have an equation which explains why acids corrode most metals.)
3 H₂SO₄ + 2 Al → Al₂(SO₄)₃ + 3 H₂ H₂ is hydrogen gas thats why there are bubbles
Use and Abuse of aluminum: What is an "alum"?
A combination of aluminum sulfate and a group 1A metal sulfate
Small Scale Techniques: Be able to describe the observations of OTO (from Chlorine test kit) with tap water and water passed through the Brita® filter. Explain.
When OTO was added to the tap water, it turned yellow showing that there was chlorine present. On the other hand when OTO was added to the water passed through the Brita filter, it was no color change because there was no chlorine present.
Spectroscopy: Explain the effect on the spectrum of changing the distance from the source of light to the spectroscope.
When its closer to the spectroscope the light is more intense
Solutions and reactions: Solubility rules
compounds are soluble with: NO3-, SO42-, Cl-, Br-, or I- so these will have a product that includes H2O compounds are insoluble with: OH-, PO43-, or CO3 EXCEPT WHEN THEY ARE COMBINED WITH : Na , K , and NH4
Use and Abuse of aluminum: Write an equation which explains why carbonated (not necessarily COLAs) beverages are acidic.
CO₂ + H₂O → H₂CO₃ H2CO3 is carbonic acid
Spectroscopy: List the colors of the spectrum from the highest to the lowest frequency.
lowest to highest ROYGBV Red, Orange, Yellow, Green, Blue, Violet
Intro to Acids and Bases: In Section C you did some titrations of HCl with NaOH, using a BTB indicator. What is observed at the endpoint, and what is the overall and net ionic equation? You should be able to predict the color in each well of your titration and use calculations to support your answer. You should also know how to calculate the concentration of an unknown given titration results
HCl(aq) + NaOH(aq) → NaCl (aq) + H₂O (l) Net ionic equation: H⁺(aq) + OH⁻(aq)→H₂O(l) Endpoint: yellow color → dark blue we calculate unknown with the formula MiVi=MfVf
Spectroscopy: If you are given the wavelengths of light observed by a particular student for the hydrogen emission spectrum you should be able to (a) know and be able to use the appropriate equations to determine the frequencies and the energies associated with these wavelengths
Frequency= speed of light/wavelength (speed of light is 3.00x10^8) energy= frequency x plants constant (plants constant= 6.63x10^-3)
Use and Abuse of aluminum: You did a melting point test on the alum you made. What two things does this test tell you about your compound? Explain.
It confirms the identity of the compound and measures its purity. Impurities decrease the melting point and gives a bigger range of melting point.
Small Scale Techniques: Describe the technique of calorimetry
It is a process where a set of solutions that have known concentrations of some light absorbing substance are placed in containers. Then a solution with an unknown concentration is compared to it.
Solutions and Reactions: One of the solutions you labeled is "aqueous ammonia/ammonium hydroxide". Why is such a complicated name used? (Isn't ammonia a gas?)
It is constantly fluctuating between the aqueous ammonia and ammonium hydroxide, even though ammonia is a gas it can still be dissolved in water. It can affect stuff near it in its gas qualities without directly touching them.
Solutions and Reactions: Write out chemical equations to explain why: aqueous sodium carbonate is basic aqueous aluminum chloride is acidic aqueous potassium iodide is neutral
1. Na₂CO₃(aq) + 2 H₂O(l)→2 NaOH(aq) + CO₂(aq) + H₂O(l) 2. AlCl₃(aq) + 3 H₂O(l)→Al(OH)₃(aq) + 3 HCl(aq) 3. KI(aq) + H₂O(l)→KOH(aq) + HI(aq)
Spectroscopy: (c) be able to quantitatively compare the results of (a) and (b)—i.e., know how to calculate the % error between a student's results and Bohr's. (You will be given the Bohr equation, the Rydberg constant, Planck's constant, and the speed of light.)
% difference = [(actual - theoretical)/ actual] x 100%
Use and Abuse of aluminum: Given the overall reaction equation for the synthesis of alum and the molar masses involved, you should be able to calculate the theoretical yield. If you are given the mass of alum actually obtained, you should be able to calculate the % yield.
% yield = (g alum actually obtained / g alum theoretically produced) * 100 % theoretical can be found by: taking grams of aluminum and converting it to moles, then multiplying that by the molecular weight
Carbon Dioxide Scrubbers: Given the mass of the scrubber and the volume of CO2 absorbed, be able to calculate the absorption capacity.
Absorption capacity= (g of CO2 absorbed/absorber)
Intro to acids and bases: Explain the difference between a "serial" titration and a "single well" titration. Cite one advantage of each type.
In a serial well, it is a process. One drop is added to the first well then 2 to the second then so on. It has the advantage of having an accurate result because you can see exactly where the titration took place. In a single well, you have a larger quantity of just one well where you just constantly add drops until titration occurs, this can be quicker because you don't have to recount for each well.
Carbon Dioxide Scrubbers Given the volume of CO2 absorbed, be able to calculate the corresponding mass of CO2. You will be given the Ideal Gas Constant (R), but no other constants or formulas.
PV=nRT
Chromatography: Be able to calculate Rf values for developed chromatograms
Rf= (distance spot traveled)/(distance solvent travels from spotting line) large Rf = component spends more time in mobile phase small Rf = component spends more time in stationary phase
Small Scale Techniques: What is the fundamental reason why a substance absorbs visible light?
The energy of a particular photon of visible light is equal to the energy that is needed to take an electron from a low energy state to a high energy state
Calorimetry: Define calorimetry
The measurement of the quantities of heat
Spectroscopy: Explain the effect on the spectrum of changing the slit width
The thicker the slit width, the more light that can enter the spectroscope so each line on the graphing paper will be thicker
Calorimetry: When walking, an average person burns 0.453 Food Calories/mile-pounds. How many food calories does a 150-pound person burn after walking a mile? If a fully combusted cheese ball produces 5.6 Food Calories/g and an average cheese ball weighs about 1 gram, then how many cheese balls will a 150-pound person have to eat to walk a mile?
(150 lb)∙(.453C/mi-lb)=67.95 C/mi (67.95 FC/1)(1cheeseball/5.6FC)= 12.13 cheeseballs
Solutions and Reactions: Define the four major types of reactions that occur in aqueous solution and give an example of each type (be able to write a balanced reaction equation for each type)
1. Acid/Base: acid reacts with base and forms salt and water ex. HCl + NaOH --> H2O + NaCl 2. Precipitation: forms an insoluble product. ex. NaCl + AgNO3 --> NaNO3 + AgCl (s) 3. Redox: chemical species changing oxidation states. ex. 2CuSO4 + 4KI --> 2CuI (s) +I2 + 2K2SO4 oxidation: 2I-->I2 +2e- reduction: 2Cu + 2e- --> 2Cu 4. Complexation: form a complex ion ex. CuSO4 + 4NH3 --> [Cu(NH3)4]SO4
Use and Abuse of aluminum: You observed a reaction involving Crystal Drano which is a similar reaction to the one that took place in the first step of the alum synthesis. Write out this reaction equation.
2 Al(s) + 2 NaOH + 6H₂O → 3 H₂(g) + 2 NaAl(OH)₄ (its always gonna be h2 and then everything else)
Chromatography: define chromatography
A method for separating mixtures that involves a stationary and mobile phase. Substances in mobile phase are separated based on the amount of time they spent in the mobile phase compared to the amount of time spent in the stationary phase.
Carbon Dioxide Scrubbers: What are the advantages and disadvantages of lithium hydroxide and activated carbon as CO2 scrubbers?
Advantages: large surface area and it can be reused Disadvantages: CO2 is a product and it can only be used once
Use and Abuse of aluminum: Explain the difference between the corrosion of iron and the corrosion of aluminum.
Aluminum reacts quickly with oxygen and its corrosion can be stopped. Where as, iron reacts slowly and can rust because its corrosion does not stop.
Intro to Acids and Bases: You used two different types of indicators in this experiment—red cabbage extract and bromothymol blue (BTB). Be able to cite one advantage of the BTB indicator over red cabbage extract.
BTB indicator will show faster, the results are more instantaneous and the results are more accurate
Spectroscopy: What kind of energy transitions were observed in this experiment?
Electronic energy transitions (valence electrons); Another transition was the color seen by human eye to the color seen on the clear graph from the spectroscope
Calorimetry: Know how to calculate amount of energy released using E = mCΔT
E is energy m is mass in grams C is specific heat T is change in temperature
Spectroscopy: Outline in a few sentences how you calibrated your spectroscope (Section E).
First we constructed the spectroscope, the sample of excited hydrogen gas was viewed through the spectroscope. We used the graph paper to note where each line was. Finally, we plotted the four highest numbers of graph lines versus the actual wavelength and used a linear equation.
Use and Abuse of aluminum: Give two reasons why aluminum is expensive to produce, and two uses for the alum compound that you synthesized.
It can be used for textiles and cosmetics It is expensive because the production of high grade bauxite deposits occur outside the United States. and The Hall-Herout process is energy intensive.
Spectroscopy: Explain the difference between a line and continues spectrum, and give an example of a source of each type
Line: only includes certain frequencies, it is produced by excited atoms in the gas phase. ex. gas Continuous: contains all the frequencies of the emitted radiation within a region on the EM spectrum. ex. sun
Chromatography: To obtain good separations in chromatography, what factor must be maximized and what factor must be minimized?
Maximize migration so that each component is clear Minimize spreading so that the bands will be narrow and thin
Carbon Dioxide Scrubbers: Be able to predict the mass and volume of CO2 that should be absorbed by a given mass of LiOH.
PV=nRT
Solutions and Reactions: Explain the "like dissolves like" principle and know some specific examples that document your explanation.
Polar substances are able to dissolve other polar substances. Water can dissolve salt because salt is an ion and ions break up completely in solution.
Chromatography: Be able to define retention volume (Vr). What does a larger retention volume mean about a component's ability to interact with the liquid chromatography column?
Retention volume is the volume of mobile phase required to carry a component through the chromatographic system Larger retention volume means the components interact with the stationary phase stronger Smaller retention volume means the components interact with the mobile phase stronger
Solutions and Reactions: Use the "like dissolves like" principle to explain the solubility experiments that you did with ethanol, pentanol, kerosene, and water in Section B.
Since water is polar, if it dissolves in water then it is polar if it doesn't dissolve in water then it is non polar. So we put each in water to see if it dissolves. ethanol: polar water:polar pentanol:non polar kerosene:non polar
Calorimetry: What is meant by small calorie "c" and a food calorie "C"?
Small calorie "c" is a scientific calorie and it is 1000x smaller then a food calorie "C". Food calories are 1000c and it is how food is measured.
Carbon Dioxide Scrubbers: Name two situations where removal of CO2 from air is important.
Spacecrafts and submarines need it because they're high in the air in space for a long time. They can be exposed to CO2 in the air and if it is over a long period of time then it can cause unconsciousness and even death
Chromatography: Be able to name the mobile phase and stationary phases in your paper chromatography experiment and be able to use the "like dissolves like" principle to rationalize relative Rf values for dye molecules.
Stationary phase is considered the water because it absorbs water from the atmosphere and the mobile phase is the fluid that flows through the stationary phase.
Use and Abuse of aluminum: In Section B you tested for the presence of SO42−, K+, Al3+ and H2O. Be able to explain (a) how each test was performed, and (b) what should have been observed in each test.
Sulfate was tested for by reacting the alum with BaCl2. A white precipitate formed. K and H2O were tested for by the flame test. The flame turned purple which shows K in it and a popping noise was heard as the water evaporated. Al was tested for by reacting it with KOH and checking for the Al(OH)4 precipitate and by Al having an acidic pH, it made a gelatinous precipitate indicating an acidic pH H2O had the crackling when it hit the flame
Small Scale Techniques: What process removed the energy from excited food dye molecules in aqueous solution?
The extra energy is removed by the solvent molecules continuously bumping into the food dye molecules. Liquids have molecules that are close together so the molecules constantly collide so the more solvent it is the more they can collide.
Small Scale Techniques: Explain the complementary nature of absorbed/observed colors
The observed color is the color transmitted and seen where as the absorbed color is the color complimentary to the observed color and it cannot be seen
Spectroscopy: Explain the purpose of the setup of the "discharge tube"
The purpose of the setup is to be able to observe/study the color emissions by the excited atoms. Since the box is black, the colors are more visible.
Intro to acids and bases: Explain what is meant by a "back titration." Why is this a better approach than a regular titration for the analysis of calcium carbonate in egg shells. Be able to calculate the calcium carbonate content of an eggshell (given the raw data and the pertinent molar masses) —i.e., the kind of calculation you had to do in Section F.
When you add a lot of acid so that the reaction will happen quicker and when the reaction is done or you want to get to the equivalence point we add a base. 1. Calculate the number of mol of HCl added to eggshell powder 2. Calculate number of mol of HCl leftover after reaction with eggshell powder is complete 3. Subtract number of mol of excess HCl from total number of mol of HCl to determine how many mol of HCl reacted 4. Calculate amount of CaCO3 that must have been involved in the reaction with HCl
Carbon Dioxide Scrubbers: Name two sources of atmospheric carbon dioxide.
aerobic respiration decomposition of organic matter
Small Scale Techniques: Be able to use the dilution equation given in this experiment to solve dilution problems.
dilution equation= m1v1=m2v2 concentration equation= CiVi=CfVf
Spectroscopy: Describe what is meant by the term "white light," and know the wavelength range (in nm) that white light covers.
light that can be seen from human eye ranged from 400nm to 800nm
Spectroscopy: Define spectroscopy
the study of the interaction with electromagnetic radiation and water
Spectroscopy: (b) be able to use the Bohr equation to calculate the wavelengths expected for the Balmer series of the hydrogen atom,
ΔE= -Rn(1/nf^2 - 1/ni^2) Rn=2.18x10^-18
