Verna Wang Hannah Palmer CHEM 101-069 Lab 11-19-16 Stoichiometry and Limiting Reagents Lab Report Purpose: We are using the reaction of sodium hydroxide and calcium chloride to illustrate stoichiometry by demonstrating proportions needed to cause a reaction to take place. Background: Just like a recipe would call for a specific amount of one ingredient to a specific amount of another, stoichiometry is the same exact method for calculating moles in a chemical reaction. Sometimes, we may not have enough of or too much of one ingredient , which would be defined as limiting and excess reagent, respectively. Ideally, every mole of each reagent would be used up, and theoretical yield, we are assuming that every last mole of the reactants would
(1) If the crucibles were not put in the oven at the end of the experiment, there could be excess moisture trapped in the crucible. This contributes to the mass of the weighed crucible at the end of the experiment, meaning the mass would be higher than it would normally be. After calculations, it can be concluded that the moisture in the crucible shifts the data up, creating an artificially high concentration of Al3+. (2) Reading the volumetric pipet to 25.00mL is an incredibly crucial step in this experiment because it’s the only source of Al3+ that is added to the reaction. This step affects the end result when weighing the precipitate because in the reaction, the Al3+ is the limiting reagent and is in a 1:1 stoichiometric ratio with the precipitate product.
The nucleophile in this particular SN2 reaction was iodine and, as stated before, the leaving groups for 1-bromobutane and 1-chlorobutane are bromine and chlorine respectively. Bromine is a better leaving group than chlorine however, so the fact that 1-bromobutane reacted before 1-chlorobutane corresponds directly with what would be expected. As stated before, primary is more reactive than secondary and even more reactive that tertiary. This explains why no reaction/change was seen for 2-chlorobutane, 2-bromobutane, and tert-butyl-chloride. 2-bromobutane would have been expected to react next, due to bromine being a better leaving group than chlorine, then 2-chlorobutane.
Purpose: The purpose of this lab is to titrate an unknown solid acid (KH2PO4) with a standardized sodium hydroxide solution. After recording and plotting the data, the acid’s equivalence point will be recorded once the color changes. Using the equivalence point, the halfway point will be calculated, which is used to determine the acid’s equilibrium constant. The acid’s calculated equilibrium constant will be compared with the acid’s established pKa value. Eventually using the NaOH and the acid’s consumed moles, the equivalent mass will be determined.
Compare the result to the chart on the back of the urinary pH test strips bottle, and record data. Clean the stirring rod with water before moving on to the next test tube. Repeat this process for each increment (2 mL, 3mL, 4mL) Figure #1: Picture of bean solution mixed Figure #2: Picture of materials needed for the with alpha galactosidase experiment Safety considerations: Be careful with the beakers, glass stirring rod, and test tubes, as they could break easily and can cause cuts in the skin. DCP: A scatter plot will be used to display how the amount of alpha galactosidase (measured in mL) in the bean solution affects the glucose concentration (measured in mg/dL) and error bars to show the standard deviation. A line of best fit will be used to show the relationship between the glucose concentration and the amount of alpha galactosidase.
Introduction: Enzymes are biological catalysts that increase the rate of a reaction without being chemically changed. Enzymes are globular proteins that contain an active site. A specific substrate binds to the active site of the enzyme chemically and structurally (4). Enzymes also increase the rate of a reaction by decreasing the activation energy for that reaction which is the minimum energy required for the reaction to take place (3). Multiple factors affect the activity of an enzyme (1).
Rf is equal to the distance traveled by the substance divided by the distance traveled by the solvent. Since the solvent used in the developing chamber was hexanes—a non-polar molecule— the more nonpolar the substance was, the stronger it would stick to the plate. This means that the more polar a pigment was, the higher it climbed on the TLC plate and would therefore have a larger Rf. There are 3 major classes of pigments present in spinach: carotenes, xanthophylls, and chlorophylls. Since the solvent is nonpolar, we would expect carotene to have the lowest Rf, then xanthophylls, and chlorophylls would have the highest.
Celery started with a pH of 6.05 and dropped down to a pH of 5.03 after 30 drops that is not nearly as drastic as alka seltzer. But, it shows how celery does not have a buffer because of the drop in pH and is not able to create more hydroxide ions when acid is added. Liver started with a pH of 6.50 and after 30 drops the pH dropped down to 6.03 which means the drop in pH is only .47 and looks similar to the data of the positive control of alka seltzer. The data in this lab follows the hypothesis of testing the HCI of liver and celery, then liver will contain a buffer and celery will not. This conclusion can be drawn because of celery’s large drop in pH and the data’s resemblance to the water data meaning celery cannot hydrolyze ions and keep a constant pH.
The error was how fast the person was spinning the water. It could have changed the temperature of the water easily, by how much calcium chloride was dissolved. Another error was how much calcium chloride was added, it told us to add one scoop, instead of a more accurate measurement, for example, one tablespoon. The scoop could have been not filled all the way, or filled too much. To improve this experiment, we could have had accurate measurements and spinning every 10 seconds.
The end rating of the Salt #2 container was 1, which is not as high as the end rating for the positive control: 1.5. This was because salt cause the algae cells to pump water out of the cell into the hypertonic outside environment. As a result, the cell membranes inside the cell to shrivel and the cell to die. However, adding 0.5 mL of salt was probably not