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18 May 2018

159. Have each group member look up the Ksp for a different com- pound. Calculate the molar solubility. Do the numerical values suggest that the compound is soluble or insoluble? Compare answers with the solubility rules from Chapter 4, and have each group member present his or her findings to the group.

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The Behavior of Substances in Water

Part 1:

Ammonia, NH₃, is a weak electrolyte. It forms ions in solution by reacting with water molecules to form the ammonium ion and hydroxide ion. Write the balanced chemical reaction for this process, including state symbols.
From everyday experience, you are probably aware that table sugar (sucrose), C₁₂H₂₂O₁₁, is soluble in water. When sucrose dissolves in water, it doesn’t form ions through any reaction with water. It just dissolves without forming ions, so it is a nonelectrolyte. Write the chemical equation for the dissolving of sucrose in water.
Both NH₃ and C₁₂H₂₂O₁₁ are soluble molecular compounds, yet they behave differently in an aqueous solution. Briefly explain why one is a weak electrolyte and the other is a nonelectrolyte.
Hydrochloric acid, HCl, is a molecular compound that is a strong electrolyte. Write the chemical reaction of HCl with water.
Compare the ammonia reaction with that of hydrochloric acid. Why are both of these substances considered electrolytes?
Explain why HCl is a strong electrolyte and ammonia is a weak electrolyte.
Classify each of the following substances as either ionic or molecular:

KCl
NH₃
CO₂
MgBr₂
HCl
Ca(OH)₂
PbS
HC₂H₃O₂

For those compounds above that, you classified as ionic, use the solubility rules to determine which are soluble.
The majority of ionic substances are solids at room temperature. Describe what you would observe if you placed a soluble ionic compound and an insoluble ionic compound in separate beakers of water.
Write the chemical equation(s), including state symbols, for what happens when each soluble ionic compound that you identified above is placed in water. Are these substances reacting with water when they are added to water?
How would you classify the soluble ionic compounds: strong electrolyte, weak electrolyte, or nonelectrolyte? Explain your answer.
Sodium chloride, NaCl, is a strong electrolyte, as is hydroiodic acid, HI. Write the chemical equations for what happens when these substances are added to water. m
Are NaCl and HI strong electrolytes because they have similar behavior in an aqueous solution? If not, describe, using words and equations, the different chemical process that takes place in each case.

Part 2:

You have two hypothetical molecular compounds, AX and AY. AX is a strong electrolyte and AY is a weak electrolyte. The compounds undergo the following chemical reactions when added to water.

AX (aq) + H₂O (l) → AH₂O⁺ (aq) + X⁻ (aq)

AY (aq) + H₂O (l) → AH₂O⁺ (aq) + Y⁻ (aq)

Explain how the relative amounts of AX ( aq ) and AY ( aq ) would compare if you had a beaker of water with AX and a beaker of water with AY.
How would the relative amounts of X⁻ ( aq) and Y⁻ ( aq) in the two beakers compare? Be sure to explain your answer.

indigolouse566

The above is what we did in the lab

Down is the question

Today you are going to take a closer look at the light emitted from a wide variety of different types of matter. Before experimenting with these different light sources, make a large table in your lab notebook with columns listing the major regions of the visible spectrum (ROYGBIV). As you collect data by looking at different light sources, you will keep adding rows of observations into this table. The general layout should look something like this: Once you have your lab notebook ready, collect some observations about these different systems by performing the following experiment: At your bench, you should find a small handheld spectroscope through which you can split the visible spectrum apart and carefully observe each color region in the spectrum. For the first light source, set up and light the votive candle inside the metal pan (the metal pan is just to keep wax from dripping all over the benchtop). Then, look through the spectroscope at the burning candle. In your lab groups, predict what you think the emission spectrum will look like from a light source (flame) that is made by burning the ionic compound SrCI_2. With your prediction, provide a molecular-level justification that supports why you think the emission will look the way you predicted. Write the predictions and explanations down in your lab notebook (with a heading/label for your TA - as you should be doing for every activity). Fill a 400mL beaker about % of the way full with tap water and keep it near your area to use as a waste beaker for used matches and burning applicators. You should have a second beaker containing cotton-tipped applicators soaking in deionized (Dl) water (be sure the applicators are NOT placed in tap water). Into the 24-well microplate, add enough of the solid test samples that have been provided in the lab so that the solid just barely covers the bottom of each well. Be sure to record the identity of each solid you test. Note - be very careful not to cross-contaminate between wells as this will significantly skew results (even a single small crystal can cause a large contamination issue). Remove the candle and place the Bunsen burner in the center of the metal baking pan (the pan will help catch any burning solids that drip or spatter from the flame tests you will be performing). Your TA will demonstrate how to light and adjust the burner being used in our labs here at CSU (avoid fireballs in your face or your lab partner- listen to the TA's directions). To observe the flame colors, you will be placing the salts on the end of water-soaked wooden applicators. When placing the applicators into the burner flame, you only have a limited amount of time before the color will disappear and the applicator begins burning so you should be prepared to make observations as soon as you place the applicator into the burner flame. Also, while performing these steps, one member of your lab group should be observing the flame with the spectroscope while another group member handles the actual burning and observes just with their eye. You should record as much information as you can about the burning behavior including color, intensity, and any other details you notice. In your groups, predict what you think the spectrum would look like for a light-emitting diode (LED) light source. LEDs are made up of solid-state materials. What do you expect to see in the spectroscope while looking at a lit LED? Write this prediction down in your lab notebook and be sure to include a heading so your TA can find this prediction while reviewing your lab notebook pages later. Test your prediction by performing the following experiment: Setup the 9V battery and wire leads as shown below - the foam card that the LEDs are mounted may be clamped into a ring stand to hold it upright for easier viewing. Connect the alligator clips coming from the battery one LED at a time. The red alligator clip should be connected to the longer (+) lead of the LED bulb. The black alligator clip is connected to the shorter (-) lead of the LED bulb. If you reverse the wire leads, the LED will not light. Once connected to the battery, note the macroscopic color of the LED bulb that you can see with your eye, then look through the spectroscope at the lit LED bulb. As you examine the LED with the spectroscope, carefully note and rate the relative appearance/intensity of each of the color regions in the visible spectrum (ROYGBIV). After you have collected all your observations, your TA will demonstrate how to use a different type of spectroscope attached to the laptop computers (SpectroVis Plus). After your TA has demonstrated how to use the instrument, collect spectra for all the LED bulbs by following these Identify and write three (3) new and well-thought-out scientific questions related to the light emitted from a firework. For credit, these new questions MUST follow these guidelines: Questions must be molecular-level and focused on the behavior of the chemical components within fireworks Questions should be directly related to the light emission concepts covered in this lab

Gasoline is made up of hundreds of different types of hydrocarbons. From a human health perspective, the most dangerous components of gasoline are four aromatic compounds: benzene, toluene. ethylbenzene, and xylenes (commonly abbreviated BTEX). These compounds help to boost the octane level of gasoline.

a) Write a balanced electron donor half reaction for oxidation of each BTEX compound.

b) Gasoline spills often soak through the soil and come in contact with groundwater. The BTEX compound then serve as food for microorganisms. Suppose a groundwater has been contaminated with 4.9 mg/L of benzene, 5.6 mg/L of toluene, 3.5 mg/L of ethylbenzene and 0.81 mg/L of xylenes. Calculate the concentration of dissolved oxygen needed for complete oxidation of these compounds. Express your answer in mg O2/L.

c) Is the amount you calculated in part b less than or greater than the maximum concentration of DO found in water when it is in contact with air? Answer yes or no and explain.

d) When dissolbed oxygen is depleted, microorganisms are able to use other electron acceptors, including ferric iron (Fe3+). Since ferric iron is insoluble, one of the ways you can determine if iron- reducing conditions exist is by measuring ferrous iron (Fe2+), which is soluble. Calculate the concentration of ferrous iron (MW= 55.84) that would be present in groundwater assuming complete decomposition of the BTEX compounds at the concentrations listed in part b. Express your answer in mg Fe2+/L