1. Calculate the Concentration of [Fe(H2O)5SCN)]^2+ after equilibrium was reache
ID: 1010200 • Letter: 1
Question
1. Calculate the Concentration of [Fe(H2O)5SCN)]^2+ after equilibrium was reached in one of the standard solutions.
25mL of 0.2M Fe(NO3)3 added to 5 flasks.
Then following amount of NaSCN added to each flask and mixed:
Volumetric Flask #
Volume of NaSCN Solution
1
0mL
2
3mL
3
6mL
4
9mL
5
12mL
then filled by DI water.
Absorbance of each sample:
#1
0.00abs
#2
0.173abs
#3
0.491abs
#4
0.664abs
#4
0.878abs
1. Calculate the Concentration of [Fe(H2O)5SCN)]^2+ after equilibrium was reached in one of the standard solutions.
Volumetric Flask #
Volume of NaSCN Solution
1
0mL
2
3mL
3
6mL
4
9mL
5
12mL
Explanation / Answer
This experiment uses concentrated nitric acid. To contain the fumes, assemble an individual fume hood consisting of an inverted funnel connected to the water aspirator with a piece of rubber tubing. Remember that concentrated acids are dangerous, especially to skin and the respiratory system. The gas generated in the reaction is also very dangerous if inhaled. Minimize breathing any of the vapors in this experiment.
PROCEDURE
[The instructor will do the following as a demonstration. Take notes. The quantities given are for a pair of students in the lab.] Measure about one gram of solid copper on a pan balance and place the Cu in an Erlenmeyer flask. The copper should be in relatively small pieces. Place the flask in the fume hood. Add a maximum of 5 mL of nitric acid.
Measure about 10-mL of the prepared solution into a 125-mL Erlenmeyer flask. Place the flask in a cool tap water bath. Add 6 M NaOH slowly to the solution and watch the reaction. Heat may be evolved, so control the temperature to keep the reaction under control. Add NaOH until no more solid forms. Sufficient NaOH (< 5 mL) must be added to both neutralize excess acid and form the hydroxide precipitate. The reaction is complete when no more solid forms. Mix the contents of the flask by SLOWLY swirling the flask. Wash down any solid that clings to the inside of the flask with about 2-3 mL of distilled water using your distilled water bottle.
Place the flask and contents into a hot tap water bath and heat the water to boiling. Stir while heating. This dehydrates the previous precipitate. Heat until you see a separation between the solid and solution. Cool the contents of the flask and allow the solid to settle.
Decant the liquid from the solid and wash the solid with 10-15 mL of distilled water. Decant the wash water. Repeat the wash two more times. Add 6 M HCl slowly to the solid while stirring. HCl should be added until the solid just disappears. Then add 1 mL in excess.
Add about 1 g of aluminum to the contents of the flask. How can you tell if sufficient Al is “available?”
The reactions are now complete. Place several paper towels in the sink and carefully pour the contents of the flask onto the towel, collecting the solid. Place the towels and solid in the waste container. The experiment is finished!
Your report must include a balanced ‘molecular’ equation for each and every reaction that occurred, including side reactions. Correlate all observations with the chemical equations [this typically means you are to write a descriptive phrase under each formula in the equation (not water)].
Double Displacement Reactions
In the table below are the 12 solutions with which you will experiment. You are to combine all possible combinations of pairs of solutions, making and recording observations. Initially, use just a few drops of each solution into a microplate for each combination. You do not need to add a chemical to itself. Do add the chemicals to each other both ways (i.e. Add LiOH(aq) to KSCN(aq) and add KSCN(aq) to LiOH(aq). The apparent reaction may depend on sequence! You will observe that some combinations produce precipitates, some produce a gas, and others appear to do nothing (Make special note of these combinations for use in an experiment second semester.). If a precipitate forms, you need to record the color & type of precipitate. Some precipitates dissolve as more chemical is added (a complex ion may be formed). A matrix is handy for recording data in this type of experiment. [Make sure you have sufficient room to record your observations in the matrix.]
Make a table and record the color of each original solution. Also, conduct and record the color of the flame test for each original solution. [Soak a cotton swab in the solution and place it at the tip of the blue cone in the flame. Use a new swab for each solution. You might want to look at http://chemistry.about.com/library/weekly/aa110401a.htm for reference.]. Determine the pH of each original solution. [Tear about 1 cm of pH paper off the roll and place on a paper towel. Using a glass stirring rod, place a drop of solution on the pH paper. Record the pH to which the color of the wet paper indicates. Use a new piece of pH paper for each solution.] You will use this information in an experiment second semester.
1. FeCl3
2. Ba(NO3)2
3. LiOH
4. KSCN
5. H2SO4
6. AgNO3
7. Al(NO3)3
8. CuSO4
9. SrCl2
10. NH3*
11.Na2CO3
12. CoCl2
*NH3(aq) is the proper designation for NH4OH(aq) which is better to use in equations
You may use information in Chapter 4 of the text and the Ultimate Chemical Equations Handbook to assist you. For each combination that appeared to react, write a net ionic equation. Include a short observation under each chemical species written in the net ionic equations. [To decrease the total work, you may write one (1) equation for several reactions, if it is appropriate. However, please state what combination of molecular reactants are being presented.] For combinations that appear not to react, write the ionic reactants à NAR [no apparent reaction]. [Suggestion: for organizational purposes in the summary, you might want to categorize the various combinations according to the commonality of results.] From these results, devise a set of solubility rules for the cations and anions.
FeCl3
Ba(NO3)2
LiOH
KSCN
H2SO4
AgNO3
Al(N03)3
CuSO4
SrCl2
NH3
Na2CO3
CoCl2
FeCl3
Ba(NO3)2
LiOH
KSCN
H2SO4
AgNO3
Al(N03)3
CuSO4
SrCl2
NH3(aq)
Na2CO3
CoCl2
AP Chemistry DOUBLE DISPLACEMENT REACTIONS
The matrix above represents a “data” table where 0.1 M solutions of each chemical are mixed, two at a time. Using the Solubility Tables and other resources in the “Ultimate Chemical Equations Handbook,” predict what product, if any, would result. Write the formula of the product(s) in the blank. If no reaction would occur, write NR. For every combination where a reaction occurred, write a net ionic equation (NIE). Do NOT write duplicate NIEs. Before a NIE, write the formulas of the pair of chemicals that produce the predicted results.
Your score on this activity will be entered in the Lab portion of the grades. These predictions will be useful in one of the experiments in the spring semester.
1. FeCl3
2. Ba(NO3)2
3. LiOH
4. KSCN
5. H2SO4
6. AgNO3
7. Al(NO3)3
8. CuSO4
9. SrCl2
10. NH3*
11.Na2CO3
12. CoCl2
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