Chemistry Lab Final Part 2

Briefly describe the differences between the spectra you observed of ambient daylight and the fluorescent lights in the laboratory. (2-3 sentences) Comment on what this evidence tells you about how light is produced in fluorescent bulbs.

*answer last statement This evidence tells me that light produced in fluorescent bulbs is produced by the absorption of electromagnetic radiation when illuminated by an external source of radiation.

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.)

*answer last statements Light is produced by the absorption of electromagnetic radiation and by the emission of certain elements.

Do a web search for images of the line spectra for helium, argon, and neon. Make general notes about the appearance of each spectrum (describe them in 2-3 sentences each). Where are the primary (brightest) lines? Are there significant "dark" areas of the spectrum? Why/why not? (BE SPECIFIC!)

*just answer last 2 questions There are significant dark areas of the spectrum because these are areas the naked eye cannot see that helium is emitting. The visible light spectrum only provides the naked eye with some vulnerable colors, the others are where the dark gaps are.

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.

-2 valence electrons in the s subshell -general configuration is ns2 Chalcogens: -6 valence electrons -form -2 ions -located in p shell -general configuration is ns2np4

Define accuracy in 1 or 2 sentences.

Accuracy is is how close a measured value is to a true value.

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.

Carmine is a red color, it is natural, and is derived from an insect called cochineal. Two food products that include this dye are jams and ice cream.

Give the correct number of significant figures for 23.450080

8

Give the correct number of significant figures for 0.071

2

Give the correct number of significant figures for 0.0000702

3

Give the correct number of significant figures for 0.0204

3

Give the correct number of significant figures for 1.78 x 10^3

3

Give the correct number of significant figures for 100.

3

Give the correct number of significant figures for

4

Give the correct number of significant figures for 1.203 x 10^-5

4

Based on the periodic trends, which of the halogen molecules do you expect to have the shortest bond? Why?

I expect fluorine to have the shortest bond length because it forms a double bond, double bonds are shorter than the single bonds.

If your beaker, graduated cylinder, or graduated pipet was wet before each trial, would this have affected the masses of water you measured? Why or why not? Briefly explain.

If the equipment was wet before each trial, this would have affected the masses of water I measured. This is because I wouldn't have been only measuring an empty equipment tool and when I used the mass from this tool to calculate the mass of water, the numbers would be incorrect.

Suppose the sample of nickel-metal you used for the experiment was actually nickel-plated lead, how would your results have been different? What specific measurement would have yielded different results from the data you collected? Be specific! (You will need to look up the literature value for the density of lead.)

If the sample of nickel metal was actually nickel-plated, I think the density I calculated for nickel would be higher. If the sample nickel was plated the mass would be greater and would therefore change the calculated density. This could have caused an increased in the density calculated and I say this because the density of lead is approximately 11.4 g/mL.

Based on periodic trends, which halide ion, X¯, will be most stable, that is, lowest in energy? Briefly explain your reasoning.

Iodine will be most stable because it has the lowest 1st ionization energy of all the halide ions.

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.

It's important to use pencil when drawing the spotting line instead of ink because the ink from the dye would mix with other chemicals and pencil wouldn't do this.

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 79 more electrons than hydrogen but there are only a couple lines in the visible region of its emission spectra. This is because many of the lines that are actually there are too high in energy or too low in energy. This would mean that they aren't in the visible region so we can't see them with our naked eye.

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: tap water Stationary phase: rectangular piece of filter paper Analyte: the movement of a particular molecule

Define precision in 1 or 2 sentences.

Precision is based upon the reproducibility of a measurement.

Define relative standard deviation.

Tells us if the standard deviation is big or little when it is compared with the mean.

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?

The discovery of noble gases altered the periodic table by having unusual characteristic like being inert and resistant to combining to other substances. Those elements emphasize that when elements react their octet they become stable and don't need to bind to more atoms or substances.

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.

The electron transitions that make up the Balmer Series are those that go from n greater than or equal to 3 and n=2.

Answer question 6 again, but for the "Lyman series" instead of the Paschen series.

The electron transitions that make up the Lyman Series are those that go from n greater than 2 and n=1. They are found in the ultraviolet region, not the visible region.

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?

The electron transitions that make up the Paschen Series are those that go from n greater than 4 to n=3. They aren't found in the visible region of the spectrum, they are found in the infrared region.

Define standard deviation.

The measure of how much certain values vary from the true value.

Define median.

The middle number in a set of values ranging from lowest to highest. When there are 2 numbers in the middle, you divide them to get the median.

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.)

The second technique gave results that were more accurate and I did expect this. I expected this because by placing the nickel pellets in the graduated cylinder, you aren't accounting for the empty space between and because the pellets don't fit perfectly. With the second method you are able to get closer to the real volume by calculating it from the volume of water being subtracted by the volume of water plus nickel pellets.

Define range.

The smallest measurement or value to the largest measurement or 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 trend is that density increases from top to bottom.

What trend in density are you able to determine (from the pooled data) from left to right in the Periodic Table? Is there a consistent trend?

The trend would be increasing left to right and yes because as atomic number increases (atomic radius too), density follows that trend as well.

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.

This happens because at these altitudes, the levels of these gases decrease alongside air pressure.

Define mode.

Whichever value in a set is most frequent.

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.

caused female rat to form malignant tumor and it was deemed unsafe for human consumption by FDA

Now answer question 7 again, but assume the metal was actually nickelplated aluminum. (You will need to look up the literature value for the density of aluminum.)

if the sample of nickel metal was actually nickel-plated aluminum, I think the density would be only slightly lower. I think this because aluminum has a low density of 2.70 g/mL and I feel like if nickel was plated with this, it would make the nickel metal pellets a tad bit lighter. This would cause a slight decrease in mass and possibly density as well.

Define mean.

the total of the sum of all measurements divided by the total number of measurements.