pre/post lab questions
Using the Balmer-Rydberg equation (Equation 3.11 from your textbook), calculate the wavelengths and energies for the hydrogen lines corresponding to the following transitions: 2 1, 3 1, 4 1, 5 1, 10 1, 20 1,100 1, and 1000 1. Use these to estimate the value of the ionization energy for hydrogen. The ionization energy corresponds to the transition n = infinity 1. (Note: this means the electron is GONE and you have created a positive ion; hence, the term "ionization energy".)
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Using the literature values for density of nickel and isopropyl alcohol that you included with your pre-lab questions, calculate the percent error for each of your experimental density values and report the values here.
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What common feature exists in the electronic structure of elements in group 2 (the alkaline earth metals)? How about group 6 (the chalcogens)? Use electron configurations in your explanation.
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When Mendeleev started assembling the periodic table, the elements known as the "noble gasses" were not known. How did this discovery alter the periodic table? What key quantum concept(s) do these elements emphasize?
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Now, compare the spectral differences between the light from your cell phone screen vs. your cell phone flashlight. Based on the comparison you made in #5 above, what can you say about ways light is produced in your cell phone? (Comment on both the screen and flashlight functions.)
.The cell phone screen and the light emit the same line spectre.
Look up the formulas, molar masses, structures (provide them), and boiling points for pentane, isopentane, and neopentane. Comment on the IMFs for each molecule. Provide a brief explanation for the difference in boiling points among the three substances. (Be brief!)
As the amount of elements increase the boiling point decreases.
You are given a 317. mg sample of a barium chloride hydrate BaCl2·6H2O and told to heat it in order to drive off all the waters of hydration. What mass of anhydrous salt will you be left with after cooling?
BaCl2 x 6H2O mm 316.29 g/mol mass.317g mol=1x10^-3 208mg
If you conducted this experiment with a known salt: copper azide - Cu(N3)2, and recorded 1.524 g as the starting mass, calculate the mass of copper you would expect to collect after complete reaction and drying the product.
Cu(N3)2 mm=147.59 g/mol cu mm =63.55 g/mol % cu by mass = 63.55/147.59 x 100=43.06% final = 1.524 times .431 = .657 g cu
In a few sentences, describe how an effective soap removes an oil spot.
Due to the fact that oil and water do not mix, soap can suspend oil leaving it readily available. to be removed. The soap product forms molecules which traps the fats from the oils.
In a hypothetical experiment, a student did not wait long enough for all of the magnesium metal to react. How would this affect the student's final value for percent by mass of copper in the salt? Explain.
If a student did not wait long enough for all of the magnesium metal to react, this would skew the results. The oxidation reduction reaction would not be complete causing bigger numbers as results for the final value of percent by mass of copper in the salt.
Epsom salt has the formula of MgSO4·7H2O. A 10.90 g sample was heated and dried completely. After cooling the mass was 5.38 g. Using calculations, show that the experimental results confirm the formula for the hydrate (i.e., seven moles of water per MgSO4 formula unit). What is the mass percent of water in the original salt sample?
MgSO4=5.38g H2O=5.52 g .3/.044=6.81(7) MgSO4-7H2O mm MgSO4=120.4g/mol mm H2O=18g/mol mole MgSO4=.044 mol mole H2O=.3 mol .3/.044=6.81(7) MgSO4 x 7H2O=50.6% mass
What naturally occurring substance might they have used instead?
Olive oil
Without looking it up, propose a boiling point temperature for pentanol (C5H11OH). Briefly explain your reasoning.
Pentanol would have a boiling point of about 250 F because it is slightly higher than butonal
Look up phosphates as detergent additives and provide brief descriptions of a.) one reason they are desirable in detergents, and b.) one reason they are considered harmful to the environment. Draw the best Lewis structure for the phosphate anion (PO43-).
Phosphates as detergents are desirable because they chelate calcium and magnesium. Chelating agents are chemical compounds that react with metal ions to form a stable, water-soluble complex. However, these can build up in waterways and cause eutrophication that starves fish. Google lewis structure.
Provide a brief definition of "saturated solution" (1-2 sentences). Provide a hypothesis for why a saturated solution is necessary at this stage of the procedure.
Saturated solution is a solution in which no more solute can be dissolved in the solvent. Saturated solution is neccesary at this stage of procedure because if it didn't become saturated the solute would ever stop saturated.
Provide the correct name for the hydrate Na2HPO4·12H2O. Also provide the correct formula for magnesium sulfate undecahydrate.
Sodium dihydrogen phosphorous dodecahydrate and MgSO4 x 11H2O
Look up and provide brief definitions of "surfactant" and "emulsifier" and explain how they are similar/different and how they can be used in conjunction with cleaning agents.
Surfactant is a substance which tends to reduce the surface tension of a liquid in which it is dissolved in. Emulsifier is a mixture of two or more liquids that become stabilized. Surfactant are a compound used in cleaning products to lower the surface tension of water and emulsifier have similar characteristics.
Describe the intermolecular forces that lead to these properties. (i.e., what intermolecular forces lead to hydrophobic behavior? Hydrophilic?) Be specific!
The IMFs that lead to hydrophobic behavior are ldfs. Dipole-dipole and hydrogen bonding.
Commercial soaps contain many additives that would not be present in the soaps synthesized in this experiment. Provide three examples.
Titanium dioxide, fragrance and stearic acid.
Provide a minimum of three reasons that water is considered a green solvent. Also, do the same for ethanol.
Water is non toxic, benign and non flammable. Ethanol is odorless, non flammable and is a renewable resource.
In a hypothetical experiment, a student accidentally broke her glass stirring rod and used a spatula made of an alloy of iron and chromium instead. Would this be a problem? Why/why not?
Yes, this would be a problem because the acid may react with the iron and the chromium, which would skew the results of the experiment.
Which molecular model in Part A of the experiment (generic formulas ABx) had the largest bond angle(s)? Which one had the smallest bond angle(s)? Provide the formulas for your answers (ABx) and comment on whether the bond angles agree with what you expected.
ab2 had the largest bond angle-linear-180 ab4&ab6 were smallest bond angle- 90
What is the most electronegative element in Red dye #2?
oxygen
What are the five basic common geometric arrangements or shapes of 2-6 total bonding domains (no lone pairs) and what are the bond angles associated with each shape?
AB2= linear = 180 AB3= trigonal planar= 120 AB4 = tetrahedral = 109.5 AB5= trigonal bypyramidal = 90 120 AB6= octahedral = 90
Provide the names of the domain and molecular geometries formed by each of the following generic formulas, assuming lone pair.
AB2E=trigonal planar=bent AB3E=tetrahedral=trigonal bi AB2E2=tetrahedral=bent AB4E=trigonal bi=seasaw AB3E2=trigonal bi=t shaped AB2E3=trigonal bi=linear AB5E=octa=square pyramidal AB4E2=octa=square planar AB3E3.=octa=t shaped
Why do you think lone pairs of electrons create greater repulsion when located near other lone pairs or bonding pairs? Orbitals containing lone pairs of electrons require more space than orbitals containing bonding pairs. Why do you think this is the case? What does the presence of one or more lone pairs of electrons do to the bond angles in a molecule (in other words, do bond angles get larger, smaller, or remain unchanged?) Briefly explain.
lone pairs have a greater repulsion bc bonding pairs are further away from the central atom while lone pairs are placed on it lone pairs dont need to be shared with other atoms lone pairs take up more space because they only attract to one nucleus the prescence of one or more lone pairs results in the bond angles decreasing bc a lone pair tries to repel the other bond
Several pieces of zinc metal are placed on an analytical balance and found to weigh 45.219 g. They are then placed in a graduated cylinder initially containing 13.75 mL of water. The final volume is 20.02 mL. Calculate the experimental density of zinc and report the result to the correct number of significant figures. Be sure to show your work.
mass/volume
Even though mercury (Hg) has many more electrons than hydrogen (how many?) there are only a few lines in the visible region of the emission spectrum for mercury. Explain why this can be true. (Be specific.)
mercury has a low number of shells diff wavelengths are released fewer lines
Do a web search for images of the line spectra for hydrogen and mercury. Make a note of the spectral lines that appear in the visible region of the spectrum (wavelength 400-700 nm) and cite the source(s) of the information.
mercury has more colors and lines
You are given a sample of a hydrate of CaSO4. The data collected and recorded in your laboratory notebook were: Calculate the formula of the hydrate.
mm CaSO4=136.14 g/mol mmH2O=18.02 g moles CaSO4=2.2mol moles H2O=1.16 mol 2.2/1.16=1.9(2) 2CaSO4 x H2O
For the experiment you will be conducting in lab, identify the following: mobile phase, stationary phase, and analyte (what you will be spotting).
mobile phase- moves or flows when in contact with stationary phase stationary- remains in a fixed position, molecules wont move analyte- dye is being measured
A rectangular block has dimensions 27.6 cm by 14.1 cm by 12.3 cm and weighs 5.67 kg. Will it float on water? Explain your answer.
multiply first 3 #s to get cm^3 (4786.7) change kg to g for weigh # (5670) 5670/4786.7 = 1.18 that is greater than 1 so it will sink
Draw the Lewis structures for the molecular gases N2, O2, and F2. Which molecule exhibits the longest interatomic distance? Which one exhibits the shortest?
n2 is shortest f has longest
Calculate the energies and frequencies for the three lower energy transitions in joules (J). Clearly show how each wavelength (434 nm, 486 nm, and 656 nm) relates to the energy you calculated and the individual quantum numbers (n) of the transition (5 2, etc.).
..V=e/h E=-2.18x10^-18J(1/n^2F-1/n^2i) n=6->2 e=-2.18x10^-18J(1/4-1/36) e=-4.84x10^-19 v=-4.84x10^-19/6.63x10^-34=7.3x10^14 Hz
There is a fourth line in the hydrogen spectrum that corresponds to the transition from 6 2 that some people can see, but most can't. Were you able to see this fourth transition? Calculate the frequency and energy of this transition (410 nm). If you were unable to see it, provide an explanation of why you think this was the case. In what region of the electromagnetic spectrum is this transition found?
.No I was not able to see the fourth line that the transition emits because there was not enough energy. 410nm==4.1x10^-7m (6.63x10^-34)(3x10^8)/4.1x10^-7=4.85x10^-19 which is less than 7.31x10^14 Hz. This would be seen in the ultraviolet part of the spectrum.
Why is ethanol a good choice for this reaction? (Hint: think about intermolecular forces.)
Ethanol is a good choice for reaction because it is a polar molecule with strong IMFS such as dipole-dipole and hydrogen bonding.
Would you be able to conduct the procedure as described (with magnesium and acid) and successfully collect solid calcium if you started with calcium salts instead of copper salts? Briefly explain.
If I conducted the same experiment with calcium salts it would not be successful since copper is a transition metal and calcium is an alkaline metal.
if you were given barium metal to use for this experiment rather than magnesium, would you expect the experiment to be successful? What if you were given solid platinum instead of magnesium? Briefly explain your answers.
If I was given barium metal instead of magnesium, the experiment would still be successful because they are both alkaline metals with low electronegativity. On the other hand, if we were given solid platinum it wouldn't work because it is not an alkaline metal.
provide brief explanations of why soaps of Li+ and Ca2+ are or are not produced for commercial consumption.
Li+ soaps are good for commercial consumption they are efficient thickeners. Li grease is also a good lubricant and is resistant to heat. Ca2+ has similar qualities however they have low dropping points and do not have an optimal temperature range.
A 100. mg sample of the magenta hydrate CoCl2·6H2O is heated in a crucible. The pale blue, anhydrous salt (CoCl2) is obtained, and weighs 54.5 mg after being cooled to room temperature. Calculate the percent water of hydration for the hydrated salt. Confirm the empirical formula as shown above (hexahydrate).
Mass of H20=.100-.0545=.0455. %h20=.45x100/.100=45.5% H20=18.016 g/mol mass=.045g 4.5x10^-2/18.02=2.49x10^-3 CoCl2==129.7 g/mol mass=.0545g 5.4x10^-2/129.7=4.16x10^-4 2.49x10^-3/4.16x10^-4 = 6 so empircal formula is confirmed
Notice that propanol and isopropanol have the same chemical formulas. What could explain the difference in boiling points between these two solvents?
The difference in boiling points can be explained by the difference in molarmasses. As well as the different IMFS.
Rationalize the difference in boiling points (look them up) for ethylene glycol, propanol, propanal, and butane. Incorporate comments on molar mass and IMFs in your answer.
The greater the boiling, the greater the IMF molar mass is also directly correlated to the boiling point and the structure of these substances.
Look up the formulas, molar masses, structures (provide them), and melting points for methane, decane, and triacontane. Comment on the melting point data with respect to molar mass and IMFs. Which substance has the strongest IMFs? Why?
The greater the molar mass and melting point means greater IMF.
Look up and draw the structure of the detergent sodium lauryl sulfate. (Do NOT simply copy and paste a photo.) Describe how the structure of this molecule differs from the soaps you will be synthesizing in lab. Be specific! (IMFs?)
The structure is a sulfate hydrogen bonded to a hydrocarbon chain. This is different because the soaps synthesized in the lab are triglycerides that become glycerol.
What trend do you observe in the boiling points for methanol, ethanol, propanol, and butanol? Does this trend make sense, given the respective molar masses of these solvents? Which one do you think exhibits the strongest IMFs? Explain.
The trend that I observed is the boiling points increases with more carbon and hydrogen present. This makes sense because the molar mass and the boiling points are directly related. Butonal has the strongest IMFS due to its high boiling point
Based on periodic trends, which halide ion, X ̄, will be most stable, that is, lowest in energy? Briefly explain your reasoning.
cl- is the most stable
Look up and provide brief definitions of the following terms as they relate to ionic compounds: deliquescent, hygroscopic, and efflorescent. (Be brief and specific!)
diliquescent-tendacy to become a liquid hygroscopic-absorbs moisture from our and creates humidity. efflorescent-migration of salt to the surface of porous material
Consider the following chromatography data and calculate the Rf values for each dye. Distance traveled Yellow 8.62 cm Red 7.18 cm Blue 3.13 cm Solvent Front 12.37 cm 12.37 cm 12.37 cm
distance/solvent
Another block the same size as given in #3 above, but made of a different material, weighs 3.95 kg. Will it float on water? Explain.
do same thing as ^
Based on the periodic trends, which of the halogen molecules do you expect to have the shortest bond? Why?
fluorine has the shortest bond bc bond is weak
Do a web search for images of the line spectra for helium, argon, and neon. h Where are the primary (brightest) lines? Are there significant "dark" areas of the spectrum? Why/why not? (BE SPECIFIC!)
helium has fewer lines than argon and neon neon has more red lines while argon has more blue lines helium has the brightest lines dark parts on left of blue and right of red
You are given a 0.800 g sample of a hydrate of SrSO4. After heating and cooling, the sample weights 0.762 g. Calculate the formula of the hydrate.
initial=SrSO4=.8g final=SrSO4=.762g mm=183.62 g/mol moles SrSO4=.762 / 183.68=.00415 mol moles H2O=.038g / 18.02 = .0021 mol 2SrSO4 x H2O
Why is it important to use pencil when drawing the spotting line on your chromatography paper instead of ink? What would happen if you did use a pen? Briefly explain.
ink contains dye which will chromatograph with the inks being used in the experiment. a pencil will not interfere w the experiment
The visible lines you see in the emission spectrum for hydrogen are part of what's known as the "Balmer series". Look this up and explain which electronic transitions make up this series.
n=3 to n=2 n=4 to n=2 n=5 to n=2 n=6 to n=2
Another well-studied series of electronic transitions is called the "Paschen series". Look this up and explain which specific electronic transitions make up this series. Are the photons emitted during these transitions found in the visible region of the spectrum? If not, in which region of the electromagnetic spectrum are they located?
n=7 to n=3 n=6 to n=3 n=5 to n=3 n=4 to n=3 infrared
Answer question 15 again, but for the "Lyman series" instead of the Paschen series.
n=7,6,5,4,3,2,1 to n=1 ultraviolet
Only two of the following species can exist. Which ones? Why is it impossible for the remaining two molecules to be formed? (NeF2, PCl5, NF6-, XeF4)
ne cannot form anything
The mathematical procedure for combining wave functions for individual atomic orbitals is called orbital hybridization. What four atomic orbitals are combined for carbon when it makes four single bonds? What four equivalent hybrid orbitals are created this way? What is the name of the geometric shape created by these four equivalent hybrid orbitals?
one 2s and 3 2p orbitals orbitals combine to form four sp3 hybrid orbitals tetrahedral is the shape created
Calculate the percent error for the experimental density values you found for each metal during the lab experiment vs. the known, literature values. Present your calculations and results neatly organized below.
our value - literature value / literature value x 100
Draw a possible Lewis structure for the iodine heptachloride (ICl7) molecule. List two possible names for the geometric shape of this molecule. What hybridized orbitals are used by the central iodine atom?
pentagonal bipyramidal sp3d3
Look up the dye "Carmine". What color is it? Is it synthetic or natural? From what source is it derived? Name at least two food products that include this dye.
red dye and natural dye it is obtained from cochineal which is an insect living as a parasite candy and frozen meat
The earth's atmosphere is composed primarily of nitrogen (N2 78%) and oxygen (O2 21%). Look up the densities of these two gases and use those values to explain why mountain climbers get light-headed at high altitudes. (Be brief!)
since density of n is lower than o there is less o molecules resulting in loss of stable air to breathe- causes light headness
Draw a possible Lewis structure for the iodine octafluoride anion (IF8-) molecule. List two possible names for the geometric shape of this molecule. What hybridized orbitals are used by the central iodine atom? What atomic orbital(s) are used for bonding by the fluoride atoms?
sp3d4 square antiprism anticube
Look up the molecule known as "Red dye #2" or "Amaranth" online and provide a brief summary (3-5 sentences) of why Mars, Inc. (the company that makes the candy M&Ms) stopped using red dye for more than a decade in the 1980s.
stopped using red dye due to public controversry synthetic red dye was linked to cancer fda was not able to name this product a safe one so it was discontinued and replaced w orange dye
Comparing the two techniques for determining the density of nickel, which method gave results that are more accurate? Was this what you expected? Why/why not? (Briefly explain.)
technique 2 bc results were closest to the library value
What trend in density are you able to determine for Period 3 to Period 4 to Period 6 (that is, top to bottom in the Periodic Table)?
the density increases from top to bottom
Food dyes are used in many products. Using the internet, identify three consumer products that contain the dye known as FD&C Yellow #5. List them below and provide sources for your information.
twinkies mountain dew m&m