18.  (WCSP[x], 6 points) A student experimentally observed three (3) emission lines from a hydrogen tube in her spectroscope. One of these was a red line that was determined to have a wavelength of 664 nm. She thinks that this is due to an electron undergoing a transition from the third to the second orbit. a.  Assume that the Bohr model is correct and calculate the wavelength predicted for the n=3 to n=2 transition.  (Equations and constants are listed above.)   Enter the value in the box below.   

(WCSP24) You used a titration in the water hardness experiment.  Please respond to the following in a few words: a.  Why is a titration useful? b.  Describe what is happening at the atomic level throughout the titration. c.  How do we know that the titration is complete?

(WCSP24) Using the data below, answer the following questions by entering a single letter (a-e) in the box: a.  Which measurement is the most precise?  [blank1] b.  Which measurement has the fewest significant figures? [blank2]   Measurement ± Uncertainty (mL) a 10.5 ± 0.5 b 10. ± 1 c 1.00 ± 0.02 d 500 ± 100 e 250.0 ± 0.1

Edit the abstract below by selecting the sentences that should be removed in the final draft. (WCSP24) Single replacement reactions occur when a single element reacts and takes the place of another element in a compound. I learned about stoichiometry when I did this experiment.  Herein, the synthesis of copper from aluminum and copper(II) sulfate is described. 5.0 g of aluminum were added to 50 mL of copper(II) sulfate.  Once the chemical reaction was balanced, I was able to determine the amount of moles of each reactant used when undergoing the reaction to produce copper. The mass of copper isolated was 1.5 g giving a yield of 86%. This lab was super fun!  

(WCSP24) Predict whether each of the molecules below is polar or nonpolar.  a) Cl-Cl   [drop1] b)   [drop2] c)  [drop3]

7.  A chromatography experiment was used to determine components in a mixture. a.  Calculate the Rf values for spot A and spot B using your ruler. Show your work. Use appropriate significant figures in your measurements and calculations.  (6 points, WCSP24.[x])    b. The stationary phase for the previous chromatogram was cellulose, which is highly polar due to the presence of multiple hydroxyl (OH) groups.  The mobile phase was water.  Given this, identify which amino acid (a building block for proteins) shown below corresponds to A and B.  Explain your reasoning. (6 points)   Enter the Rf value of spot A in the box below.

19.  (WCSP[x], 5 points) Hydrogen bonding is responsible for many of the interesting and unusual properties of water. Draw a picture showing hydrogen bonding in liquid water.  Use three water molecules in your drawing and dashed lines to depict the hydrogen bonding interactions. Enter the number of hydrogen bond donor-acceptor interactions in the sketch.  

(WCSP24) Explain the “like dissolves like” principle. Use at least two specific examples in your explanation.

In the 1910s, a massive immigration of blacks from south to north occurred as a result of

Whenever Jamia sees someone wearing traditional Middle Eastern clothing or a woman with a hijab, she gets very upset. She will cross the street to avoid them and turn down another aisle in the store to avoid them. If she accidentally comes close to someone she believes is Muslim or Middle Eastern she gets nervous and has to leave immediately. What is Jamia experiencing?