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13 Dec 2019

Take four test tubes from the Containers shelf and place them on the workbench.

Fill each test tube with a different halide solution from the Materials shelf, as directed below. You may want to label the test tubes by double-clicking on each test tube and renaming it.

Test Tube # Halide Solution

1 10.5 mL 0.1 M sodium chloride

2 10.5 mL 0.1 M sodium fluoride

3 10.5 mL 0.1 M sodium iodide

4 10.5 mL 0.2 M potassium bromide

Take 0.5 M calcium nitrate from the Materials shelf and add 4.5 mL to each of the four test tubes. You may want to use the + or – zoom buttons in the lower right of the screen for a closer view. Record any evidence of a reaction with each of the four halide ions in your Lab Notes. Remember to press Save Notes.

Dispose of the four test tubes by dragging them to the recycling bin beneath Experiment 1: Observe the Reactions Between Halide and Calcium Ions

the workbench.

Experiment 2: Observe the Reactions Between Halide and Silver Ions

Prepare another set of four test tubes with the halogen ions as described in steps 1 and 2 of experiment 1.

Take 0.1 M silver nitrate from the Materials shelf and add 4.5 mL to each of the four test tubes. Observe and record any evidence of a reaction with each of the four halide ions in your Lab Notes. You may want to zoom in for a closer look.

Dispose of the four test tubes by placing them in the recycling bin.

Experiment 3: Observe the Reactions Between Silver Halides and Ammonia

Take four 50 mL beakers from the Containers shelf and place them on the workbench.

Fill each beaker with a different halide solution from the Materials shelf, as directed below. You may want to label the beakers by double-clicking on each one and renaming it.

Beaker # Halide Solution

1 10.5 mL 0.1 M sodium chloride

2 10.5 mL 0.1 M sodium fluoride

3 10.5 mL 0.1 M sodium iodide

4 10.5 mL 0.2 M potassium bromide

Take 0.1 M silver nitrate from the Materials shelf and add 4.5 mL to each beaker. Observe and record any evidence of a reaction with each of the four halogen ions in your Lab Notes.

Take 4 M ammonia from the Materials shelf and add 4.5 mL to each beaker. Observe and record any evidence of a reaction with each of the four halogen ions in your Lab Notes.

Dispose of the four beakers by placing them in the recycling bin.

Experiment 4: Observe the Reactions Between Silver Halides and Sodium Thiosulfate

Prepare another set of beakers with the halide ions as described in steps 1 and 2 of experiment 3.

Take 0.1 M silver nitrate from the Materials shelf and add 4.5 mL to each beaker. Observe and record any evidence of a reaction with each of the four halogen ions in your Lab Notes.

Take 0.2 M sodium thiosulfate from the Materials shelf and add 4.5 mL to each beaker. Observe and record any evidence of a reaction with each of the four halogen ions in your Lab Notes.

Dispose of the four beakers by placing them in the recycling bin.

Experiment 5: Identify Unknown Halides

On the Materials shelf, there are two unidentified halide solutions. Each solution contains one of the four halide ions from the previous four experiments. Identify them using the reagents and

Questions

1. Suppose you forgot to label your test tubes and you do not remember their order. Can you identify the sodium fluoride solution using only the reaction with silver nitrate?

a. Yes sodium floride will form a white precipitate with silver nitrate

b. No both sodium floride and potassium bromide will form a yello precipitate with silver

c. Yes sodium floride will not form a precipitate with silver nitrate

d. No sodium floride does not form a precipate with silver nitrate

2. How can you identify the sodium chloride containing test tube using only the reactions with silver nitrate?

a. Sodium chloride does not form a white pecipate with silver nitrate

b. Sodium chloride forms a pale yellow precipitate with silver nitrate

c. Sodium chloride forms a yellow precipate with silver

d. Sodium chloride forms a white precipate with silver nitrate

3. Which of the following statements are true?

a. Silver nitrate fomed precipates in the presence of floride,bromide and iodine ions

b. Silver nitrate formed precipates in the presence of chloride, bromide, and fluoride ions

c. Silver nitrate fomed precipates in the presence of chloride, floride, and iodine ions

d. Silver nitrate fomed precipitaes in the prensence of chloride,bromide and iodine ions

4. If you were allowed to react your unknown halides with only one of the reagents used in this lab, which reagent will you pick and why?

a. Ammonia because it forms colored precipitaes with both halides

b. Silver nitrate because it forms different color precipitates with the two halides

c. Calcium nitrate because it forms a precipate with only one of the halides

d. Sodium thiosulfate because it changes the color of the halide solutions

5. How would you expect the results to change if the identity of the cation were to change?

a. There would be increased solubility in the prensence of ammonia

b. There would be no change since these test are for the halide ion

c. The next change of the solution would increase

d. There would be increased precipation of the halide ion upon the addition of silver nitrate

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17 Dec 2019

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Related questions

Note: For the calculations you will perform in the assignments you will assume that, because this solution is very dilute, its density is the same as pure water: 1 g/mL. Therefore, there are 20 mg of starch per mL in the 2% solution.

**Post Lab Question: Plot out your data using a Michaelis-Menton curve. Appropriately label the x- and y-axes (which also includes the appropriate units). Try to draw a best fit curve using your knowledge.

The experimental Data is listed below. In addition to the experimental instructions that were followed. I have updated the lab instructions. This was a LateNite Lab (website) assignment. Please answer the Post Lab question using the provided information. If you think the questio is too long, than anser as much of the qustion as you can. My professor considers this to b one question.

Data:

Experiment #1:

Cuvette #1: 1.03

Cuvette #2: 0.51

Cuvette #3: 0.26

Experiment #2:

Test Tube #1: 2.97

Test Tube #2: 4.69

Test Tube #3: 6.21

Test Tube #4: 7.21

Test Tube #5: 8.33

Experiment #3:

Test Tube #1: 1.03

Test Tube #2: 0.96

Test Tube #3: 0.36

Test Tube #4: 0.40

Test Tube #5: 0.83

Experiment #4:

Test Tube #1: 0.66 / Temperature 10 Celsius / pH 7.21

Test Tube #2: 0.24 / Temp 37 Celsius / pH 7.21

Test Tube #3: 0.33 / Temp 50 Celsius / pH 7.21

Test Tube #4: 1.03 / Temp 80 Celsius / pH 7.21

About This Lab

In this lab, you will use spectrophotometry to follow the reaction of the amylase enzyme on starch molecules. You will examine the effects that environmental pH and temperature have on the rate of amylase digestion of starch. This will be observed by using iodine to test for the presence of starch. Iodine interacts with starch to form a dark blue-black color. As amylase breaks down starch, less and less starch is present, so the color of the iodine test solution becomes lighter and lighter until only the amber color of iodine will be seen.

In order to stop the reactions at a specific time, a strong acid, HCl, is added to the amylase solution. As the pH falls below the functional pH of the enzyme the reaction stops.

Procedures

Experiment 1: Creating a Calibration Curve for Starch-Iodine Measurements

1 Take three cuvettes from the Containers shelf and place them onto the workbench.

2 Take an Erlenmeyer flask from the Containers shelf and place it onto the workbench.

3 Add 0.25 mL of the 2% starch solution from the Materials shelf to the Erlenmeyer flask. Note: For the calculations you will perform in the assignments you will assume that, because this solution is very dilute, its density is the same as pure water: 1 g/mL. Therefore, there are 20 mg of starch per mL in the 2% solution.

4 Add 99.75 mL of water from the Materials shelf to the Erlenmeyer flask to obtain a dilute solution that is 1/400th the concentration of the original 2% starch solution on the shelf.

5 Using the dilute starch solution from the Erlenmeyer flask on the workbench and the iodine solution found on the Materials shelf, fill the three cuvettes as follows:

6 Exp. 1 Cuvette Set-up

7 Cuvette Name

8 Dilute Starch Solution (mL)

9 Iodine (mL)

Cuvette #1: 4ml Dilute Starch; 1ml Iodine

Cuvette #2: 2ml Dilute Starch; 3ml Iodine

Cuvette #3: 1ml Dilute Starch; 4ml Iodine

Take a spectrophotometer from the Instruments shelf and place it onto the workbench. Using the control panel:

◦ Select the Vis button. A button that is selected has a gray background and blue font. The "Mode" should change to Vis in the view screen.

◦ Set the wavelength to 620 nm:

▪ Click on the number under "Wavelength" in the view screen. The preset value should disappear and a flashing cursor should appear.

▪ Type in 620.

▪ Press Enter.

◦ Confirm that the A button is selected.

20 Blank the spectrophotometer:

◦ Take a cuvette from the Containers shelf and place it onto the workbench.

◦ Add 5 mL of water from the Materials shelf to the cuvette.

◦ Move the water cuvette into the spectrophotometer's loading well where it says "open". The digital display will show the absorbance once the lid closes.

◦ Use the water as your blank solution by clicking the Zero.

◦ Press the Open button on the spectrophotometer's loading well to remove the cuvette. It will automatically go back to the workbench. Discard it in the recycling bin.

21 Move cuvette 1 into the spectrophotometer's loading well. The digital display will show the absorbance once the lid closes.

22 Record the cuvette's number, contents, and absorbance in your Lab Notes. Remember to press Saves Notes.

23 Press the Open button on the spectrophotometer's loading well to remove the cuvette. It will automatically go back to the workbench.

24 Repeat steps 8 – 10 to identify the absorbance of the remaining two cuvettes.

25 If you zoomed in on the spectrophotometer, press the Re-Set Zoom button in the lower right hand corner of the screen to go back to original view of the lab.

26 Discard the cuvettes and the Erlenmeyer flask in the recycling bin.

Experiment 2: The Effect of pH on Amylase Enzyme Activity

Part 1: Preparing the Reaction Solutions

1 Take five test tubes from the Containers shelf and place them onto the workbench.

2 Using items found on the Materials shelf, fill the test tubes according to the table below. These will include NaH2PO4 (monosodium phosphate), Na2HPO4 (sodium hydrogen phosphate), and NaHCO3 (sodium bicarbonate).

3 Exp. 2 Reaction Solutions:

Test Tube #1: 6ml 0.1 M Acetic Acid (mL); 1ml Water (mL); 2ml 2% Starch Solution (mL)

Test Tube #2: 6ml 0.1 M NaH2PO4 (mL); 1ml Water (mL); 2ml 2% Starch Solution (mL)

Test Tube #3: 5ml 0.1 M NaH2PO4 (mL); 0.5ml 0.1 M Na2HPO4 (mL); 1.5ml Water (mL); 2ml 2% Starch Solution (mL)

Test Tube #4: 3ml 0.1 M NaH2PO4 (mL); 3ml 0.1 M Na2HPO4 (mL); 1ml Water (mL); 2ml 2% Starch Solution (mL)

Test Tube #5: 1ml Water (mL); 6ml 0.1 M NaHCO3 (mL); 2ml 2% Starch Solution (mL)

Take a pH meter from the Instruments shelf and attach it to test tube 1. If you need a closer look, press the Zoom In button in the lower right hand corner of the screen. Record the pH in your Lab Notes. Remember to press Saves Notes.

47 Repeat step 3 with the remaining test tubes.

48 Discard the pH meter in the recycling bin.

Part 2: Amylase Reactions

1 Take two cuvettes from the Containers shelf and place them onto the workbench.

2 Fill the first cuvette with 4.5 mL of 6 M HCl and the second cuvette with 4.5 mL of iodine solution from the Materials shelf.

3 Add 1 mL of amylase solution from the Materials shelf to test tube 1. Immediately click on the clock icon on the lower left of your workspace to start a timer.

4 After 1 minute, add 0.5 mL of the reaction solution in test tube 1 into cuvette 1, which contains the HCl. Remember, the HCl will stop the reaction between the amylase and the starch.

5 Add 0.5 mL of the reaction solution from cuvette 1 into cuvette 2, containing the yellow iodine solution.

6 Confirm that your spectrophotometer is set to:

◦ Vis

◦ 620 nm

◦ A

7 Insert cuvette 2 into the spectrophotometer and record the absorbance in your Lab Notes. Remember to press Saves Notes.

8 Remove the cuvette from the spectrophotometer by pressing the Open button on the spectrophotometer's loading well. It will automatically go back to the workbench.

9 Discard both cuvettes on the workbench into the recycling bin.

10 Repeat the procedure outlined in steps 1 – 9 for the four remaining reaction test tubes.

11 When you are finished, keep the spectrophotometer on the workbench, and discard all the other items.

Experiment 3: The Effect of Temperature on Amylase Enzyme Activity

1 Take a constant temperature bath from the Instruments shelf and place it onto the workbench. Set it by pressing the white circular button until it reaches 10 C.

2 Take a test tube from the Containers shelf and place it onto the workbench.

3 Add the following components from the Materials shelf to the test tube:

◦ 3 mL NaH2PO4

◦ 3 mL Na2HPO4

◦ 2 mL 2% starch solution

◦ 1 mL water

4 Move the test tube into the constant temperature bath.

5 Take a thermometer from the Instruments shelf and place it into the test tube.

6 Repeat steps 1 – 5 for three more constant temperature baths, set at 37 C, 50 C, and 80 C, respectively.

7 Place the thermometers in the recycling bin once the temperatures in the test tubes have stabilized at the same temperature of the bath they are in.

8 Take two cuvettes from the Containers shelf and place them onto the workbench.

9 Fill the first cuvette with 4.5 mL of 6 M HCl and the second cuvette with 4.5 mL of iodine solution from the Materials shelf.

10 Add 1 mL of amylase solution from the Materials shelf to test tube 1 in its bath. Immediately click on the clock icon on the lower left of your workspace to start a timer.

11 After 1 minute, remove test tube 1 from its bath and place it on the workbench. Add 0.5 mL of the reaction solution from test tube 1 into cuvette 1, containing the HCl, to stop the reaction.

12 Add 0.5 mL of the reaction solution in cuvette 1 into cuvette 2, containing the yellow iodine solution.

13 Insert cuvette 2 into the spectrophotometer. Confirm that your spectrophotometer is set to:

◦ Vis

◦ 620 nm

◦ A

14 Record the absorbance and constant bath temperature in your Lab Notes.

15 Remove the cuvette from the spectrophotometer by pressing the Open button on the spectrophotometer's loading well. It will automatically go back to the workbench.

16 Take a pH meter from the Instruments shelf and place it into the test tube and record the pH in your Lab Notes. Remember to press Saves Notes.

17 Discard the two used cuvettes, the test tube with pH meter, and the constant temperature bath.

18 Repeat steps 8 – 17 for the remaining test tubes.


Experiment 1: Standardize an NaOH Solution Using Benzoic Acid as Primary Standard

Part 1: Prepare the NaOH Solution

Take a 250 mL beaker from the Containers shelf and place it on the workbench.

Take sodium hydroxide from the Materials shelf and add 0.800 g to the beaker.

Take water from the Materials shelf and add 200 mL to the beaker.

Calculate the expected concentration of the sodium hydroxide solution. The molar mass of NaOH is 39.997 g/mol.

Calculate and record the expected mass of benzoic acid required to react with 20.00 mL of a 0.100 M sodium hydroxide solution. Record the mass of benzoic acid using three significant digits

Part 2: Perform a Coarse Titration

Take a clean Erlenmeyer flask from the Containers shelf and place it on the workbench.

Take water from the Materials shelf and add 100 mL to the Erlenmeyer flask.

Add the required mass of benzoic acid calculated in step 5 of part 1 to the Erlenmeyer flask. The 100 mL of water should be enough to dissolve the solid benzoic acid.

Take phenolphthalein from the Materials shelf and add 2 drops to the Erlenmeyer flask.

Take a pH meter from the Instruments shelf and place it into the flask. Record the initial pH of the solution.

Take a burette from the Containers shelf and place it on the workbench.

Take the prepared sodium hydroxide solution from the workbench and add 50 mL to the burette. Pass the mouse cursor over the burette and a gray tool tip will briefly display the total volume in the burette as well as the volume dispensed. Record these initial volumes.

Move the Erlenmeyer flask onto the base of the burette.

Perform a coarse titration, adding large increments of titrant (~ 2 mL) by pressing and holding the stopcock at the bottom of the burette for 1-2 seconds. Pause after each dispensation. Record the volume dispensed.

Check if the end point has passed. When the reaction reaches the end point, the solution changes color. Also, as sodium hydroxide is added to the benzoic acid solution, the pH increases.

Stop once you reach the end point. Record the volume dispensed and pH at which this occurs. Record both the last dispensed volume where the solution was colorless (right before the end point) and the first dispensed volume where the solution changed color. You will use the volume dispensed before the end point in the fine titration.

Discard the Erlenmeyer flask by dragging it to the recycling bin beneath the workbench.

Part 3: Perform Fine Titrations

Prepare an Erlenmeyer flask as described in steps 1 - 5 in part 2 of experiment 1.

Take sodium hydroxide solution from the workbench and refill the burette to a total volume of 50 mL. Record this initial volume.

Move the Erlenmeyer flask onto the base of the burette.

Click and hold the stopcock of the burette to quickly add the before the end point volume of sodium hydroxide determined in the coarse titration.

Add titrant in small increments, down to one drop at a time. This can be tedious, but if you click and hold you might miss the exact end point of the titration.

When the solution changes color, stop adding titrant. Record the pH and volume dispensed.

Clear your workstation by dragging the Erlenmeyer flask to the recycling bin.

Repeat the fine titration two more times, and record the results.

Calculate the concentration of the sodium hydroxide solution. The rest of the sodium hydroxide solution can now be used in further lab work as a secondary standard with a reliably known concentration equal to the average of the three titrations.

Experiment 2: Use the Standardized NaOH Solution to Determine the Concentration of an Acid

Part 1: Perform a Coarse Titration

Take an Erlenmeyer flask from the Containers shelf and place it on the workbench.

Take acetic acid #1 (unknown concentration) from the Materials shelf and add 25 mL to the flask.

Take phenolphthalein from the Materials shelf and add two drops to the flask.

Take a pH meter from the Instruments shelf and place it into the Erlenmeyer flask. Record the pH.

Take the NaOH solution from the workbench and refill the burette to a volume of 50 mL. Pass the mouse cursor over the burette and a gray tool tip will briefly display the total volume in the burette as well as the volume dispensed. Record these volumes.

Move the Erlenmeyer flask onto the base of the burette.

Perform a coarse titration, adding large increments of titrant (~ 2 mL) from the burette by pressing and holding the stopcock at the bottom of the burette. Pause after each dispensation. Record the volume dispensed.

Check if the end point has passed. When the reaction reaches the end point, the solution changes color. Also, as more sodium hydroxide is added to the acetic acid solution, the pH increases.

Stop once you reach the end point. Record the dispensed volume and pH at which this occurs. Record both the last dispensed volume where the solution was colorless (right before the end point) and the first dispensed volume where the solution changed color. You will use the volume dispensed right before the end point in the fine titration.

Clear your station by dragging the Erlenmeyer flask to the recycling bin.

Part 2: Perform Fine Titrations

Set up the titration as described in steps 1 – 6 in part 1 of experiment 2.

Click and hold the stopcock of the burette to quickly add the before the end point volume of sodium hydroxide determined in the coarse titration.

Add sodium hydroxide in small increments, down to one drop at a time. This can be tedious, but if you click and hold you might miss the exact end point of the titration.

When the solution changes color, stop adding titrant. Record both the pH and volume dispensed.

Clear your station by dragging the Erlenmeyer flask to the recycling bin.

Repeat the fine titration twice more

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