Chem Lab final 116
Which of the the TLC solvents shown in the picture would be the best to choose to separate unknowns using a microcolumn?
(picture) the one with the most separation
Which of the following should you look out for PRIOR to starting your titration? -All of the above -Loose O-rings -That the stopcock is horizontal before adding titrant -Air bubbles in the tip of the buret
all of the above
What is the main carbohydrate found in milk? (Type carefully, you must spell it correctly.)
lactose
If a reaction evolves 556.06-J of heat as 0.024-moles of water are produced, what is the \Delta H ΔH of this reaction (in kJ/mol)? Report your answer to 2 decimal places.
23.17
A tablet generated 0.002 moles of CO2. If that tablet had an initial mass of 0.5-g, what percent of the tablet was bicarbonate? Report your answer to 3 decimal places.
24.4
Separations are considered sufficient if there is
obvious space between the components being tested. Here, you can see that there is plenty of space between the components, so this separation would be considered sufficient.This point was covered in the video for this week's lab.
What is the ratio of citric acid (HCit) and sodium hydroxide (NaOH) based on the balanced chemical equation?
3 NaOH: 1 HCit
Report the volume of liquid contained in the graduated cylinder to the correct number of decimal places. DO NOT include units in your answer.
the correct number of decimal places is two ex:4.90 not 4.9
Decide which of the following would be the BEST for the individual performing this experiment to record for the reaction product represented in the picture.
(picture) would be yellow precipitate
Calculate the Rf value for the measured spot on this TLC plate. Report your result to 2 decimal places.
(picture) would take the smaller number(on the bottom) and divide by bigger number (on the top)
How much heat (in J) is evolved when two solutions are mixed together to give 34.79-g of solution and a temperature change of -5 degrees Celsius? Report your answer to 2 decimal places, and the sign on your answer should correspond to the change in temperature.
-727.81
Which of the following is a specific safety precaution that you must take this week? -Take care with the sulfuric acid; it is a strong, concentrated acid and could cause severe skin burns if exposure occurs. -Take care with the glacial acetic acid; it can cause skin burns and irritate the respiratory system. -All of these are specific safety precautions that you must take this week. -Take care when smelling the esters; it is important to waft the odor towards you so that you don't sniff the vapors directly.
-All of these are specific safety precautions that you must take this week.
-When 'washing' your filtered product, you should turn the vacuum off before adding the 'wash' solvent to remove as many impurities as possible. -You must clamp the funnel to the ring stand prior to using it. -When filtering a solid, you should add the 'wash' solvent to the glassware that originally held the solid and filtrate before adding it to the funnel. -You should wet the filter paper with the same solvent that is in your filtrate prior to turning on the vacuum. -You are limited to only the amounts of 'wash' solvents that are listed in the manual. which is wrong?
-You are limited to only the amounts of 'wash' solvents that are listed in the manual.
Which of the following tasks can be performed at the same time (check all that apply)? -titration -thin layer chromatography -UV-Vis spectroscopy -My group will do them all separately because we like to take as much time as possible to complete the lab.
-titration -thin layer chromatography -UV-Vis spectroscopy
How many moles of Aspirin are present in a tablet that has 250-mg of active ingredient?
0.0014 moles
How many moles of CO2 gas are generated if you collect 35.52-mL of the gas over water at 26 degrees C and 1.02-atm?
0.0015
What is the citric acid concentration in a soda if it requires 32.23-mL of 0.01-M NaOH to titrate 25-mL of soda?
0.0043
How many moles of phosphate were isolated from a sample of milk if 1.124-g of calcium phosphate were isolated after the completion of exercise 3? Report your answer to 4 decimal places and WITHOUT units.
0.0072 mol
What mass of copper sulfate pentahydrate is necessary to produce 25 mL of a solution with a concentration of 0.02 moles per liter?
0.125
A reaction involving acetic acid has an enthalpy change of 55.7 kJ/mol. What is the concentration of 33.42-mL of this acetic acid solution if the reaction it is involved in evolves 621.44-J of heat? Report your answer to 2 decimal places
0.33
Calculate the theoretical yield of aspirin given that 0.914-g of salicylic acid was reacted with excess acetic anhydride. REPORT YOUR ANSWER TO 2 DECIMAL PLACES!
1.19
To how many decimal places should the volume on the buret be read (hint: it is graduated the same way that the Mohr pipet is)?
2
Fill in the blanks with the BEST required coefficients to balance the chemical equation. (If there is no coefficient needed, enter a 1 in the blank). ____NaNO3(s) → ___NaNO2(s) +___O2(g)
2, 2, 1
What is the molar mass of KHP?
204 g/mol
How many mL of 0.01-M NaOH will be required to titrate 0.06-g of KHP to it's endpoint?
29.412
Jack and Jill are lab partners. Jill delivered 8.19 mL of a 19.97 % sugar stock solution using a graduated pipette into a 25-mL volumetric flask. Distilled water was added to the graduation mark on the flask and mixed well. What was the final concentration of the resulting solution?
6.54
Which of the following pH's is most reasonable for a titration of a strong base and weak acid that uses phenolphthalein as an endpoint.
9.0
A positive result for the FeCl3 test should result in which of the following observations? in isolation of aspirin and preparation of flavoring esters
A deep purple solution
Excess of which of the following reagents should be placed in the designated chemical waste containers?
Acetone
What type of sample(s) should be included on the TLC plate? -Salicylic acid -Commercial aspirin -Your synthesized aspirin -All of the above
All of the above
Which of the following statements best describes the spot size you should aim for when spotting your TLC plates with the dyes? -As large as possible -As small as possible -It doesn't matter
As small as possible
Which of the following would be considered the analyte in this week's lab?
Both NaOH and Citric acid
Which of the following types of molecules will give a positive result for the Benedict's test?
aldehydic sugars
Adding the bicarbonate solution to the organic acid should result in which of the following noticeable changes?
Evolution of gas
According to your lab manual, which of the following experimental steps MUST be carried out in the fume hood because of the risk of bumping.? -Adding approximately 7-mL of NaOH to the filtrate from exercise 1. -Adding acetic acid to the milk sample in Exercise 1. -Heating the precipitate from Exercise 1 in acetone. -Performing the Benedict's test on the control and treatment test tubes.
Heating the precipitate from Exercise 1 in acetone.
In what order should the following steps be performed for a successful recrystallization? I. Place the beaker with the aspirin in an ice bath. II. Add the chilled second solvent slowly until you see a few crystals. III. Dissolve the synthesized aspirin in the solvent it's most soluble in. IV. Weigh the purified aspirin and calculate the percent yield.
III, II, I, IV
Which of the following statements best describes the proper disposal of the microcolumn? -In the trash, without paper towels. - In the glass waste, wrapped in paper towels. -In the glass waste, without paper towels. - In the trash, wrapped in paper towels
In the glass waste, without paper towels
Why is the addition of the bicarbonate solution necessary when making the flavoring esters?
It is added to react with excess acetic acid so the acid doesn't mask the smell of the ester.
Which of the following statements best describes the line you will create on the bottom of your TLC plate? - It should be made in black ink about an inch from the bottom of the plate. - It should be made in pencil about a centimeter from the bottom of the plate. - It should be made in pencil about an inch from the bottom of the plate. - It should be made in black ink about a centimeter from the bottom of the plate.
It should be made in pencil about a centimeter from the bottom of the plate.
What is the most likely cause of water not being displaced in the buret once the tablet has been dissolved?
Leaks in the system; fix them with parafilm.
in the milk lab What should you do if you measure 55.3 mL (59.4 g) of milk?
Record the mass and press on because you care more about exact mass than exact volume here.
in copper amine synthesis and UV-vis spec lab You will prepare solutions this week using a volumetric flask. What should you do if you add water too quickly and your solution goes above the graduation line?
Start weighing another sample of copper sulfate because you need to start over.
Why is the addition of cold distilled water to the container holding the aspirin you are trying to isolate a necessary step and why should this step be carried out carefully? -The aspirin is less soluble in water than ethanol- the water keeps the crystals from separating from solution. -The aspirin is less soluble in ethanol than water - the water helps the crystals separate from solution. -The aspirin is more soluble in ethanol than water - the water helps the crystals separate from solution. -The aspirin is more soluble in water than ethanol- the water keeps the crystals from separating from solution.
The aspirin is more soluble in ethanol than water - the water helps the crystals separate from solution.
-You must stir moderately fast so that your solution doesn't 'bump'. -The beaker should be cool enough that you can remove it from the hot plate with your bare hands. -You will need to heat and cool your beaker more than once to ensure that the fat is separated from the protein. -You will need to periodically replenish your acetone throughout the heating process. -The mixture should be heated on the lowest hotplate setting. which is incorrect for exercise 2?
The beaker should be cool enough that you can remove it from the hot plate with your bare hands.
Which solution should be added to the calorimeter first? for the heat of reaction lab
The excess reagent
Which of the following is NOT included in the next ionic equation we are using this week? heat of reaction lab
The soluble salt
In order to start Exercise 2 for the milk lab, you need to...
Use the precipitate from Exercise 1.
How will you know that the pressure of your system is equalized and that it is okay to record an initial and/or final volume?
When the meniscus in the funnel is level with the meniscus in the buret.
Your manual mentions Dalton's Law of Partial Pressures. If you attribute all of the generated gas to CO2 production, which of the following statements is true? -Your calculated value for the generated CO2 will be lower than it actually is because you are not considering the vapor pressure of water. -Your calculated value for the generated CO2 will be higher than it actually is because you are not considering the vapor pressure of water. -Your calculated value for the generated CO2 will represent the actual value because you are not considering the vapor pressure of water. -I like soup.
Your calculated value for the generated CO2 will be higher than it actually is because you are not considering the vapor pressure of water.
The function group R-COOH is referred to as an organic --___and the functional group R-OH is referred to as a generic _____
acid, alcohol
What color should be observed when a small drop of basic solution is touched to litmus paper?
blue
For this experiment (copper amine sun and UV-vis) , you will graphically determine how the concentration of a solution affects absorption. Which response represents the values of the independent (x) and dependent (y) axes that will be on the graph you prepare, respectively.
concentration (M), absorbance
Which of the following scenarios was NOT mentioned as a possible troubleshooting point in the technique video?
crushing the tablet with a mortar and pestle is difficult.
The following reaction can BEST be described by which of the categories listed below? N2O5(s) ® NO2(g) + O2(g) Gas Formation Reduction/Oxidation Precipitation
gas formation
The following reaction the BEST be described by which of the categories listed below? HC2H3O2(aq) + NaHCO3(aq) → NaC2H3O2(aq) + H2O(l) + CO2(g) - Acid/Base -Reduction/Oxidation -Gas Formation
gas formation
Which of the following answers lists the components for the microcolumn in the order you should add them. - glass wool, sand, silica gel, sand, solvent and dye -glass wool, sand, silica gel, solvent and dye, sand - glass wool, silica gel, sand, solvent and dye, sand -glass wool, solvent and dye, sand, silica gel, sand
glass wool, sand, silica gel, solvent and dye, sand
What are the most dominate intermolecular forces present in water?
hydrogen bonding
Which of the following statements regarding the collection and use of pH data during this week's lab is FALSE? -Determining the pH of the solution before mixing is useful for determining the identity of an unknown solution. -pH data should be collected following completion of all of the reactions. -The pH cannot be used to definitively identify an unknown if the pH units are close together. -It is not possible to take the pH of a solid piece of met
pH data should be collected following completion of all of the reactions
What color should the solution containing your analyte turn when the endpoint of the titration has been reached? (characterization and analysis of aspirin)
pink
Methanol (CH3OH) molecules are capable of hydrogen bonding. Would this be an example of a polar or a nonpolar solvent?
polar
A lab group made a copper amine stock solution with a concentration of 0.02 M. A group member transfers 7.59 mL of this solution to a 25 mL volumetric flask and dilutes to the line with water. What is the concentration of the resulting solution?
0.006
What is the maximum amount of gas that your apparatus can collect? (In other words, how much water should you aim to displace?) (bicarbonate content in an antacid tablet)
35-45 mL
Carey is using an aluminum cylinder as a counter weight. He would like to know the mass of the cylinder, but does not have a balance available. Knowing that his cylinder displaced a volume of 13.02 mL and that the density of aluminum is known to be 2.7 g/mL, what is the mass of his cylinder
35.15 g
What is the MINIMUM temperature change that is acceptable to record in your manual? for heat of reaction lab
4 degrees C
A laboratory group began the recrystallization process with. 0.964-grams of synthesized aspirin. After they carefully completed the necessary steps to purify their sample via recystallization, they were left with 0.497-grams of aspirin. What is the group's percent yield? REPORT YOUR ANSWER TO 2 DECIMAL PLACES.
51.56
Which of the following definitions DOES NOT describe a catalyst? -A small amount of catalyst will make a significant change in rate. -A catalyst is not consumed in the reaction. -A catalyst speeds up the rate of a chemical reaction. -Adding a catalyst ensures a much larger yield of product.
Adding a catalyst ensures a much larger yield of product.
Review the following image and report what insoluble compound is likely leading to the opaque nature of the solution following the initial addition of aqueous ammonia.
Cu(OH)2 (picture)
Two clear/colorless solutions are mixed quantitatively. No noticeable precipitate or gas is observed, and the reaction is performed on a small scale (in a well plate). The lab group should record "no reaction" in their notebook.
False
Why of the following statements regarding the citric acid titration is NOT CORRECT? -The soda solution should be cooled to room temperature before beginning your titration. - It is necessary to boil the soda prior to beginning your titration. - It is not necessary to know the exact amount of soda added to the flask. -The carbonation in the soda can react with NaOH and cause your calculations to be wrong.
It is not necessary to know the exact amount of soda added to the flask.
Based on your existing knowledge of TLC, which of the following statements regarding the thin layer chromatography portion of this experiment is NOT CORRECT? -The solvent that aspirin is less soluble in should be used as the mobile phase. -The Rf values of the spots are all fairly close together. - The sample spots are only visible under a UV lamp. -You will need to draw around the spots on the plate while it's under the UV lamp.
The solvent that aspirin is less soluble in should be used as the mobile phas
Which statement BEST describes the relationship between the spots that are developed on the TLC plate and the spots that are separated by the microcolumn? -The spots will appear in the same order (ex: blue,pink and blue, pink) on both the TLC plate and the microcolumn because we add solvent from the top in one and the bottom in the other. -The spots will appear in the same order (ex: blue,pink and blue, pink) on both the TLC plate and the microcolumn because we are using the same solvent. -The spots will appear in opposite order (ex: blue,pink and pink, blue) on the TLC plate and the microcolumn because we are using two different solvents. -The spots will appear in opposite order (ex: blue,pink and pink, blue) on the TLC plate and the microcolumn because we add solvent from the top in one and the bottom in the other.
The spots will appear in opposite order (ex: blue,pink and pink, blue) on the TLC plate and the microcolumn because we add solvent from the top in one and the bottom in the other.
Which statement BEST describes the relationship between the spots that are developed on the TLC plate and the spots that are separated by the microcolumn? The spots will appear in the same order (ex: blue,pink and blue, pink) on both the TLC plate and the microcolumn because we add solvent from the top in one and the bottom in the other. The spots will appear in the same order (ex: blue,pink and blue, pink) on both the TLC plate and the microcolumn because we are using the same solvent. The spots will appear in opposite order (ex: blue,pink and pink, blue) on the TLC plate and the microcolumn because we are using two different solvents. Correct! The spots will appear in opposite order (ex: blue,pink and pink, blue) on the TLC plate and the microcolumn because we add solvent from the top in one and the bottom in the other.
The spots will appear in opposite order (ex: blue,pink and pink, blue) on the TLC plate and the microcolumn because we add solvent from the top in one and the bottom in the other.
Which of the following statements regarding the Benedict's Test for Reducing Sugars is INCORRECT? -The provided 1% glucose solution is used as a positive control. - This test will give a positive result for any sugar. -The contents of the test tubes can be disposed of down the sink. -This test tells you only whether or not sugar is present in the sample; you cannot determine a quantity. -You should set up your water bath for this portion of the experiment at the beginning of the lab period.
This test will give a positive result for any sugar.
