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Lab: Spectroscopy and Qualitative Analysis in the Determination of an Unknown Iron Salt
Procedure
Part A:
Obtain one of the provided kits and inspect for completeness (see available list in the laboratory). Ask your instructor for replacement items if necessary. Select one of the available unknown iron salts. All of the iron salts (which may or may not be hydrated) are in the +2 oxidation state and will have one of the following anions: Cl^-, Br^-, SO4^2- and CH3COO^- (acetate). Finally, obtain ~ 30 mL of the standard iron(II) solution (record the concentration).
2. Using the 10 mL beaker, weigh out ~ 0.0400 to 0.0500 g (±0.0001 g) of your salt. Record the mass dispensed. Transfer the salt to a 100.00 mL volumetric flask using a small amount of water. Rinse the beaker 3 to 4 times; transferring the washings to the flask each time. Allow the iron salt to completely dissolve and then dilute to the mark.
3. Using the pipette from your kit, transfer 1.00 mL of the solution from step 2 into a 100.00 mL volumetric flask. To the flask add 1 mL each of: 1% hydroxylamine hydrochloride solution, 1 M sodium acetate and 1% 1,10-phenanthroline solution from the provided burettes. Dilute to the mark and mix thoroughly. This is the unknown solution you will measure the absorbance of.
4. Rinse and fill a burette with the standard iron solution obtained in step 1. Prepare the standard solutions as follows: accurately dispense – recording initial and final burette readings (±0.02 mL) – approximately 1.00, 2.00, 3.00 and 4.00 ml of the standard Fe^2+ solution into separate volumetric flasks. As in step 3, add 1 mL each of: 1% hydroxylamine hydrochloride solution, 1 M sodium acetate and 1% 1,10-phenanthroline solution from the provided burettes. Dilute to the mark and mix thorougly.
5. Using the final 100.00 mL volumetric flask, prepare the blank solution by adding 1 mL each of: 1% hydroxylamine hydrochloride solution, 1 M sodium acetate and 1% 1,10-phenanthroline solution from the provided burettes. Dilute to the mark and mixthoroughly.
6. To analyze your samples ask the lab demonstrators for instruction on the proper use of the spectrophotometer. Obtain the absorbance of each of the standards and the unknown at 508 nm.
Part B:
Qualitative Analysis
Transfer some of your salt (tip of a scoopula) into a beaker and dissolve it in ~ 30 mL distilled water. If you are finding it difficult to dissolve your salt, add two to three drops of 6M HNO3 and mix.Transfer equal portions (about 2-3 cm in height) of this solution into two test tubes:
1. Chloride and Bromide. Add 3 drops of 6M HNO3 to the solution in the first test tube and shake well. Add 5 drops of 0.1M AgNO3 and mix well. If a precipitate has formed upon the addition of silver nitrate a positive test for chloride or bromide has occurred. If no precipitate formed you do not have either the chloride or bromide salt and can move on to the sulfate test. To differentiate between chloride and bromide, add 10 drops of 6M NH4 OH to the mixture (do not mix). If two distinct layers form immediately, then the chloride anion is present.
2. Sulfate. Add 3 drops of 6M HNO3 to the solution in the second test tube and shake well. Add 5 drops of 0.1M BaCl2. The formation of a white precipitate indicates the presence of SO4^2-.
3. Acetate. Place a small amount of the solid salt (~ the size of a pea) into a test tube. Add 20 drops of concentrated H2SO4 (CARE!!!) and 20 drops of 1-pentanol from the dropper bottles in the fume hood to the test tube and mix with a glass stirring rod. Place the test tube in the water bath provided (making a note of which one is yours) for about 5 minutes. Remove the test tube from the bath and check the odour of the solution by bringing your nose slowly to the test tube and waving your hand over the top of the test tube towards your nose. You can also pour it onto a watch glass to make it easier to pick up the odour. A fruity odour (it often reminds people of fake banana smell) indicates the presence of the acetate ion.
_______My Data Below
Concentration of standard iron(II) solution = 50.0 ppm
Weight of unknown salt: 0.0413 g (+- 0.0001 g)
| Fe^2+ Solution (mL) | Volume (final)-Volume (initial) = Change in Volume (+- 0.04 mL) |
| 1.00 | 1.01 |
| 2.00 | 1.89 |
| 3.00 | 3.02 |
| 4.00 | 4.01 |
| Fe^2+ Solution (mL) | Calculated Concentration (ppm) | Absorbance (a.u. |
| 1.00 | 0.505 | 0.079 |
| 2.00 | 0.945 | 0.198 |
| 3.00 | 1.51 | 0.304 |
| 4.00 | 2.005 | 0.410 |
| Unknown solution | 1.35 | 0.267 |
The positive ion test determined that the unknown salt was sulphate (SO4^2-).
Question: Using the mass of the sample analyzed, the dilutions you performed and the positive anion test determine: the identity of your unknown salt, its molecular weight and the water of hydration.
In: Chemistry
Calculate the appropriate amount of 28 wt% aqueous NH3 and solid NH4Cl to be mixed together to yield 500 ml of a ~0.2 M pH 10 buffer. Check with pH paper. Store in a flask and adjust pH as needed.
In: Chemistry
Consider the reaction A+2B⇌C whose rate at 25 ∘C was measured using three different sets of initial concentrations as listed in the following table: Trial [A] (M) [B] (M) Rate (M/s) 1 0.20 0.010 4.8×10−4 2 0.20 0.020 9.6×10−4 3 0.40 0.010 1.9×10−3 What is the rate law for this reaction? Express the rate law symbolically in terms of k, [A], and [B].
Calculate the initial rate for the formation of C at 25 ∘C, if [A]=0.50M and [B]=0.075M.
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Q. A certain amino acid has the following elemental composition: C, H, O, N. In a combustion analysis, 3.263g of it was combusted to produce 5.910g of CO2 and 2.835g of H2O. Separate analysis determined that it is 19.17% N, and its molar mass is 150g/mol. Determine its empirical and molecular formula.
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1) Write the net ionic equation for the equilibrium that is established when ammonium iodide is dissolved in water. (Use H3O+ instead of H+.) This solution is acidic, basic or neutral?
2)Write the net ionic equation for the equilibrium that is established when calcium nitrite is dissolved in water. The solution is acidic, basic or neutral?
3)Write the net ionic equation for the equilibrium that is established when barium cyanide is dissolved in water. This solution is acidic, basic or neutral?
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A sample of solid Ca(OH)2 was stirred in water at a certain temperature until the solution contained as much dissolved Ca(OH)2 as it could hold. A 78.7-mL sample of this solution was withdrawn and titrated with 0.0696 M HBr. It required 68.0 mL of the acid solution for neutralization.
(a) What was the molarity of the Ca(OH)2 solution?
_________M
(b) What is the solubility of Ca(OH)2 in water, at
the experimental temperature, in grams of Ca(OH)2 per
100 mL of solution?
_________g/100mL
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Calculate [H30+] and [S2-] in a 0.1 M solution of the diprotic acid hydrosulfuric acid. (For hydrosulfuric acid Ka1 = 9.0 times 10-8 and Ka2 = l.OxlO-17.) Enter your answers in scientific notation. [H3O+] = times M [s2-] = times M
In: Chemistry
What does it mean to calculate the average value of the rate
constant from the four data sets ? What is average value of the
rate constant. What does this mean??
This is about Kinetics in Chemistry.
Also how do I compare the rate of appearance to the rate of
disappearance. Do i look at moles ? All of them appear to be
gases
In: Chemistry
You prepare a buffer solution from 10.0 mL of 0.100 M MOPS (3-morpholinopropane-1-sulfonic acid) and 10.0 mL of 0.079 M NaOH. Next, you add 1.00 mL of 5.67 × 10^-5 M lidocaine to this mixture. Denoting lidocaine as L, calculate the fraction of lidocaine present in the form LH+.
MOPS Ka = 6.3 × 10^–8.
Lidocaine Kb = 8.7 × 10^–7
(Hint: First calculate the pH of the solution from the amount of MOPS added. Start by finding the number of moles (or millimoles) of HA and OH–. Which reactant is limiting? Next, find the amount of A– that forms and the amount of HA left over. Finally, determine the [A–]/[HA] ratio and use the Henderson-Haselbalch equation to find pH. The concentration of lidocaine is too low to affect this pH value. Calculate the pKa of lidocaine and then the fraction in the protonated form from the pH and the pKa using the Henderson Hasselbalch equation.)
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On a cold, dry morning after a frost, the temperature was -5C and the partial pressure of water in the atmosphere fell to 0.30 kPa. Will the frost sublime? What partial pressure of water would ensure that the frost remained?
In: Chemistry
|
Heat Capacity Learning Goal: To understand the concepts of heat capacity, specific heat, and molar heat capacity. Heat capacity, C, is the amount of energy required to raise the temperature of a substance by exactly 1 degree Celsius. The energy needed to warm an object increases as the mass of that object increases. We see this in our everyday life. For example, we know that it takes much more energy to heat a large tank of water than a small cup. Because of this dependence on mass, experimentally determined heat capacities are always reported in terms of the amount of the substance that is heated. One method is to report how much energy it takes to raise the temperature of one mole of a substance by exactly 1 degree Celsius. This value is the molar heat capacity, which has the symbol Cp.The molar heat capacity is given in the units J/(mol⋅∘C). A second method is to report how much energy it takes to raise the temperature of one gram of a substance by exactly 1 degree Celsius. This value is the specific heat, which has been given the symbol Cs. The units for specific heat are J/(g⋅∘C).The heat capacity of a substance is therefore related to the energy q needed to raise its temperature by an amount ΔT. That is, q=nCpΔT, where n denotes the number of moles of the substance, or q=mCsΔT, where m denotes the number of grams of the substance. |
Part A It takes 51.0 J to raise the temperature of an 11.1 g piece of unknown metal from 13.0∘C to 24.3 ∘C. What is the specific heat for the metal? Express your answer with the appropriate units.
SubmitHintsMy AnswersGive UpReview Part Parts B and C The next two questions pertain to silver. They have nothing to do with unknown metal described in Part A. Part B The molar heat capacity of silver is 25.35 J/mol⋅∘C. How much energy would it take to raise the temperature of 11.1 g of silver by 15.8 ∘C? Express your answer with the appropriate units.
SubmitHintsMy AnswersGive UpReview Part Part C What is the specific heat of silver? Express your answer with the appropriate units.
SubmitHintsMy AnswersGive UpReview Part |
In: Chemistry
Determine the pH of a solution after 20.00 mL of 0.4963 M HI has been titrated with 12.64 mL of 0.5174 M NaOH.
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In the following reaction, 451.4 g of lead reacts with excess oxygen forming 321.9 g of lead(II) oxide. Calculate the percent yield of the reaction. 2Pb(s)+O2(g)-->2PbO(s)
In: Chemistry
Preparation of CuCl
Reactions: 1) Cu(S) + 4HNO3(aq) -> Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l) 2) 2HNO3(aq) + Na2CO3(s) -> H2O(l) + CO2(g) + 2NaNO3(aq) 3)Cu(NO3)2(aq) + Na2CO3(s) -> CuCO3(s) + 2NANO3(aq) 4)CuCO3(s) + 2HCL(aq) -> CuCl2(aq) + H2O(l) + CO2(g) 5)CuCl2(aq) + Cu(s) -> 2CuCl(s)
Weight of copper: 1.023g
Volume of Added Nitric Acid: 5.5 mL
Total weight of added Sodium Carbonate: 3.85g
Weight of Watch Glass and filter paper: 51.533g
Weight of Watch Glass, Filter Paper and CuCl Precipitate: 53.524
Experimantal Yield of CuCl: 1.991g
Theoretical Yield of CuCl: 3.187g CuCl
Percent Yield of CuCl: 62.47%
1) Based on the amounts of copper metal and nitric acid you used in the 1st reaction, calculate the number of moles of HNO3 there are in excess. Concentrated nitric acid has a concentration of 15.8 M.
2. Using the moles of HNO3 you calculated and the moles of Cu(NO3)2 produced from the 1st reaction, calculate the total mass of sodium carbonate needed for the second and third reactions. Did you add enough sodium carbonate in the experiment?
3. What observation suggests that copper was added in excess during the last reaction?
4) Why might a student obtain a percent yield less than 100% for this preparation?
5) Copper metal reacts with dilute nitric acid by the following reaction.
3Cu(s)+ 8HNO3(aq) ->3Cu(NO3)2(aq) + 2NO(g) + 4H2O(l)
If this reaction took place rather than the 1st reaction, would your yield of CuCl be affected assuming you started with the same amount of copper metal? Explain your answer.
6) Could we use HCl to dissolve the copper metal instead of nitric acid in the first reaction? Explain your answer.
7) Given the following three sequential reactions:
a) N2(g) + 3H2(g) -> 2NH3(g)
b) 4NH3(g) + 5O2(g) -> 4NO(g) + 6H2O(g)
3) 2NO(g) + O2(g) -> 2NO2(g)
What mass of hydrogen gas is needed to produce 165.0 kg of nitrogen dioxide?
In: Chemistry