Alonzo Eric Lab 5 PDF

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Determining the formula of Hydrates...

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CHEM1111-07 10/25/20

Experiment #5 Determining Formula of Hydrates

Eric Alonzo Lab Partner(s): Cade Bauer, David Berlin

Procedure The necessary materials for this experiment shall include the following:        

Safety equipment to include goggles, gloves, a face shield, and adequate ventilation, Clean, dry crucible with a cover, Mass scale, Samples of CuSO4 hydrate, CoCl2 hydrate, and CaCl2 hydrate, Disposable weighing tray, spatula, and crucible tongs, Ring stand, ring, and clay triangle to place over Bunsen Burner, Pipette and access to water, Cleaning materials and paper towels.

In Part I of the experiment, find the tare weight of the crucible to be used to heat the hydrate, and record the mass in grams. Weigh the crucible and approximately one gram of the initial hydrate sample, CuSO4, to determine mass of the crucible and the sample and record. Support the crucible containing the hydrated CuSO4 on a ring stand over a Bunsen Burner. Heat the crucible briefly and observe and record the color change of the sample as the water is being driven off of the hydrate. Turn off the heat and allow the crucible and contents to coll. Re-weigh the crucible and the CuSO 4 sample and record the new mass. Repeat the above steps until there are two measurements within 0.050 grams. Transfer the dehydrated sample to the weighing tray and add water. Observe and record any changes. Clean all equipment. Repeat all steps as outline for Part II, evaluating the formula of CoCl2 hydrate, and Part III, evaluating the formula of CaCl2 hydrate. Clean all equipment and return to proper place in lab. Properly dispose of all waste. Use data and observations to complete the determination of the hydrate formula for each of the samples.

Data and Observations Part I. CuSO4•xH2O Mass of crucible: 27.73 g Initial mass of CuSO4•xH2O

28.86g-27.73g(crucible mass) = 1.13 g CuSO4•xH2O 28.40g-27.73g (crucible mass) = 0.67g CuSO4•xH2O 28.40g-27.73g(crucible mass)= 0.67g CuSO4•xH2O

Mass of CuSO4•xH2O after 1st heating Mass of CuSO4•xH2O after 2nd heating Add more trials if necessary Appearance of the dehydrated product: Initially, the hydrated CuSO4 appeared bright blue, however, after heating the dehydrated product appeared white. Observations after adding water to the dehydrated product: The CuSO4 again appeared bright blue.

CHEM1111-07 10/25/20

Experiment #5 Determining Formula of Hydrates

Eric Alonzo Lab Partner(s): Cade Bauer, David Berlin

Finding x in CuSO4•xH2O: 1. Determine the initial mass in grams of CuSO4•xH2O by subtracting the mass of the crucible from the total mass of the crucible plus the CuSO 4•xH2O sample: a. 28.86 g (CuSO4•xH 2O + crucible) – 27.73 g (crucible only) = 1.13 g CuSO4•xH2O. 2. Determine the mass of the anhydrate, CuSO 4, after heating the hydrate in the crucible and driving off the water. a. 28.40 g (CuSO4 + crucible) – 27.73 g ( crucible only) = 0.67 g CuSO4 . 3. Determine the mass of the H2O in the hydrate by subtracting the mass of the anhydrate. a. 1.13 g CuSO4•xH2O - 0.67 g CuSO4 = 0.46 g H2O. 4. Determine the mass percent of H2O in the CuSO4•xH2O hydrate. a. (0.46 g H2O / 1.13 g CuSO4 •xH2O) * 100 = 40.1% 5. Determine the number of moles of the CuSO4 and the H2O in the hydrate by dividing the mass weight of each component by the respective molar mass. a. 0.67 g CuSO4 / 159.6 = 0.004198 moles CuSO4 b. 0.46 g H2O / 18 = 0.02554 moles H2O 6. Determine the ratio of the number of moles of each component by dividing by the smaller number of moles of the compound. a. 0.0042 moles CuSO4 / 0.0042 moles CuSO4 = 1. b. 0.0255 moles H2O / 0.0042 moles CuSO4 = 6.

7. According to the observed experimental results, the formula is: CuSO4• 6H2O. 8. The known formula for the hydrate of CuSO4. is CuSO4• 5H2O (cupric pentahydrate). Please see the discussion on potential sources of error. A possible source of error is insufficient heating or overheating of the hydrate, or possibly the sample reabsorbed some moisture from the air in the cooling process due to the ambient humidity in the lab which would cause the number of moles of the water to be higher than expected.

Part II. CoCl2•yH2O Mass of crucible: 27.73 g Initial mass of CoCl2•yH2O Mass of CoCl2•yH2O after 1st heating Mass of CoCl2•yH2O after 2nd heating Add more trials if necessary

28.66g-27.73 g (crucible mass) = 0.93 g 28.34 -27.73 g (crucible mass) = 0.61 g 28.24-27.73 g (crucible mass) = 0.51 g

CHEM1111-07 10/25/20

Experiment #5 Determining Formula of Hydrates

Eric Alonzo Lab Partner(s): Cade Bauer, David Berlin

Appearance of the dehydrated product: Initially the hydrate appear to be red and after heating, the dehydrated product appeared blue. Observations after adding water to the dehydrated product: After adding water back to the dehydrated product it turned red again. Finding y in CoCl2•yH2O: 1. Determine the initial mass in grams of CoCl 2•yH2O by subtracting the mass of the crucible from the total mass of the crucible plus the CoCl 2•yH2O sample: a. 28.66 g (CoCl2•yH2O + crucible) – 27.73 g (crucible only) = 0.93 g CoCl2•yH2O. 2. Determine the mass of the anhydrate, CoCl2, after heating the hydrate in the crucible and driving off the water. a. 28.24g (CoCl2 + crucible) – 27.73 g ( crucible only) = 0.51 g CoCl2 . 3. Determine the mass of the H2O in the hydrate by subtracting the mass of the anhydrate. a. 0.93 g CoCl2•yH2O - 0.51 g CoCl2 = 0.42 g H2O. 4. Determine the mass percent of H2O in the CoCl2•yH2O hydrate. a. (0.42 g H2O / 0.93 g CoCl2•yH2O) * 100 = 45% 5. Determine the number of moles of the CoCl2 and the H2O in the hydrate by dividing the mass weight of each component by the respective molar mass. a. 0.51 g CoCl2/ 129.84 = 0.003928 moles CoCl2 b. 0.42 g H2O / 18 = 0.0233 moles H2O 6. Determine the ratio of the number of moles of each component by dividing by the smaller number of moles. a. 0.003928 moles CoCl2 / 0.003928 moles CoCl2 = 1. b. 0.02333 moles H2O / 0.003928 moles CoCl2 = 6.

7. According to the observed experimental results, the formula is: CoCl2 • 6H2O. 8. The known formula for the hydrate of CoCl2. is CuSO4• 6H2O (cobalt (II) chloride hexahydrate). Please see the discussion on potential sources of error.

Part III. CaCl2 • zH2O Mass of crucible: 27.73 g Mass of lid: 10.49 g Initial mass of CaCl2•zH2O Mass of CaCl2•zH2O after 1st heating Mass of CaCl2•zH2O after 2nd heating Add more trials if necessary

28.68 g-27.73 g (crucible mass) = 0.95 g 28.32 g -27.73 g (crucible mass) = 0.59 g 28.26 g -27.73 g (crucible mass) = 0.53 g

CHEM1111-07 10/25/20

Experiment #5 Determining Formula of Hydrates

Eric Alonzo Lab Partner(s): Cade Bauer, David Berlin

Appearance of the dehydrated product: The product initially appeared as white clusters, and after being heated the dehydrated product appeared as a white powder. Observations after adding water to the dehydrated product: When water was added to the dehydrated product it dissolved. Finding z in CaCl2•zH2O: 1. Determine the initial mass in grams of CaCl2•zH2O by subtracting the mass of the crucible from the total mass of the crucible plus the CaCl2•zH2O sample: a. 28.66 g (CaCl2•zH2O + crucible) – 27.73 g (crucible only) = 0.95 g CaCl2•zH2O. 2. Determine the mass of the anhydrate, CaCl2, after heating the hydrate in the crucible and driving off the water. a. 28.26g (CaCl2+ crucible) – 27.73 g ( crucible only) = 0.53 g CaCl2 . 3. Determine the mass of the H2O in the hydrate by subtracting the mass of the anhydrate. a. 0.95 g CaCl2•zH2O - 0.53 g CaCl2= 0.42 g H2O. 4. Determine the mass percent of H2O in the CaCl2•zH2O hydrate. a. (0.42 g H2O / 0.95 g CaCl2•zH2O) * 100 = 44% 5. Determine the number of moles of the CaCl2 and the H2O in the hydrate by dividing the mass weight of each component by the respective molar mass. a. 0.53 g CaCl2/ 110.98 = 0.004776 moles CaCl2 b. 0.42 g H2O / 18 = 0.0233 moles H2O 6. Determine the ratio of the number of moles of each component by dividing by the smaller number of moles. a. 0.004776 moles CaCl2 / 0.004776 moles CaCl2= 1.

b. 0.02333 moles H2O / 0.004776 moles CaCl2 = 5. 7. According to the observed experimental results, the formula is: CaCl2 • 5H2O. 8. The known formula for the hydrate of CaCl2. is CaCl2•2H2O Please see the discussion on potential sources of error. In this case, it is likely that the sample was possibly heated too long causing some of the salt to splatter, resulting in a higher proportion of moles of water relative to moles of the salt. This can cause the percentage of water in the hydrate to seem larger than it is known to be.

Potential Error Sources Possible sources of error could be that the anhydrous product could have reabsorbed some of the moisture from the air prior to measurement during the cooling process. This could be minimized by ensuring that the lab environment is low humidity and weighing the sample as soon as possible, however, the ambient humidity could be considered an inherent error. Another source of error might be absorption of water prior to the experiment commencing.

CHEM1111-07 10/25/20

Experiment #5 Determining Formula of Hydrates

Eric Alonzo Lab Partner(s): Cade Bauer, David Berlin

It is also possible that the sample was not heated sufficiently to evaporate all of the water in the hydrated crystals. In order to ensure that no water remains in the crystal, it may be necessary to reheat the sample several times and reweigh the sample to determine the total weight and ensure that all the water has been eliminated. Similarly, if the sample is overheated, some of the anhydrous salt can be lost, in which case there will be less than is expected. As a result, the percentage of water will seem larger than it actually is and the number of moles of water to salt in the linear formula will be too high. During heating, some of the hydrous salt may have splattered, thus removing a portion of the salt from the crucible, which could adversely affect the calculations of the ratios and the mass percentages. Using a larger crucible might help to reduce splatter. Human error is always a possibility, and there is the possibility of inaccuracies in measurement to include inaccuracy in weighing of the crucible, which would propagate to an inaccuracy in the mass weight calculations of all of the samples and their components. It is possible that the scale used to measure the crucible and the crucible plus the sample was not accurately calibrated prior to the lab. Checking the calibration of the scale with known standard weights is a way to correct for this type of error, especially for small sample sizes (sample size was approximately one gram). Possible improvements include increasing the sample size, repeating all measurements multiple times, ensuring that the accuracy of all equipment is known, ensuring that the crucible is not warm before introducing the sample which can affect the measurement.

Postlab Questions 1.

CoCl2 is often used in hygrometers. Suggest why. A hygrometer is a weather instrument used to measure the amount of humidity in the atmosphere CoCl2 is used in hygrometers because the substance has the ability to change colors when the humidity levels in the air change. It relates to the experiment because in the experiment we learned that CoCl3 is a hydrate and we observed that hydrates have the ability to change color when hydrated and dehydrated.

2.

Are the dehydration and hydration of the three salts used in the experiment reversible? Use experimental results to support your claim. Yes, both the dehydration and the hydration results in this experiment are reversible. They were reversed throughout the experiment. The dehydration result was reversed by adding water drops to the crucible. The dehydration process was also slightly reversed by simply leaving the crucible out since the solution would absorb moisture from the air. The hydration process was also reversed by heating the solution which was in the crucible to boiling after adding the droplets of water.

3.

Find the expected formulas for hydrates: CuSO4•xH2O, CoCl2•yH2O, and CaSO4•zH2O when they are freshly purchased (use websites such as www.aldrich.com).

CHEM1111-07 10/25/20

Experiment #5 Determining Formula of Hydrates

Eric Alonzo Lab Partner(s): Cade Bauer, David Berlin

The formula for freshly purchased cupric sulfate pentahydrate from the above website is CuSO4•5H2O. Information on the website describes some synonyms for cupric sulfate pentahydrate as blue vitriol, copper(II) sulfate pentahydrate, and copper salt (1:1) pentahydrate. The linear formula is as previously described ( CuSO4•5H2O ). The Molecular weight is reported as 249.69. The formula for freshly purchased CaSO 4•zH2O, or calcium sulfate dihydrate is CaO4S · 2H2O. Information on the website regarding this compound includes the molecular weight, which is listed as 172.17, purification standards of the various products, and US Pharmacopeia (USP) reference standards.

4. If you had not heated the sample long enough to remove all the water of hydration, how would your subsequent calculations have been affected (explain why)? If the hydrate sample is not heated long enough, you won’t get all the water to evaporate which means that the final product will still contain some water. The calculated mass (difference between the weight of the hydrate sample and the heated sample) will be smaller than it should be, and this will affect the calculation to have a smaller percentage of water for the hydrate, since the ratio between the remaining mass and the evaporated water will be larger than it should be. The result will be the incorrect number of moles of water for the formula, with the number of actual moles of water being less than 5 moles of water per 1 mole of anhydrous cupric sulfate....