Often the color of transition metal like cobalt’s color will change as a function of how many waters it is attracted to. Compounds containing water (H2O) of hydrated are written with water separate by a dot (. ). This (. ) means for hydrated metal salt there are how many number of moles of water bound to each mole of that metal salt. Research Question: The aim of this experiment is to calculate the number of moles of water bounded to each mole of cobalt chloride ( CoCl2. H2O). This cobalt chloride hydrated may be monohydrate with 1 mole of water attracted to cobalt chloride.
It may be dihydrate, trihydrate, tetrahydrate or pentahydrate; your task is to determine which one you are given. Hypothesis: If cobalt chloride were heated until there is no further lose in weight, 6 moles of water would be lost from 1 mole of salt. Therefore it is predicted that there are 6 moles of water in this reaction. Materials (Apparatus): 1. 3 gram of cobalt chloride 2. Evaporating dish 3. Tongs to hold the evaporating dish 4. Ring stand 5. Iron ring 6. Clamp 7. Bunsen burner 8. Matches 9. 40. 20 g size of the crucible 10. Digital balance/ g 0. 01 11.
Clay triangle 12. Gloss rod Procedure: 1. Place an empty crucible on digital balance by uncertainty of 0. 01g 2. Measure the size of the crucible without salt 3. Add 3 gram of cobalt chloride to the crucible 4. Measure the total size of crucible containing cobalt chloride 5. Take the crucible containing salt, place it on the Bunsen burner by tongs. Place crucible on a clay triangle and iron ring to protect the crucible from falling. 6. Gently heat the crucible by Bunsen burner 7. Use a gloss rod to give a movement to cobalt chloride to crystalized. 8.
Record time for salt crystallization 9. Stop heating when cobalt chloride crystalized 10. Wait for few second for crucible to cool down 11. Place and Measure the anhydrous crucible by digital balance 12. Using calculation find the number of moles in this reaction. CoCl2 . nH2O CoCl2 + nH2 Data Collection and Processing: Process| Observation during the experiment | Changes in color | As we started heating the crucible containing CoCl2. H2O , the color of the CoCl2 started to change from violet purple to dark purple and the blue in 6 minutes and it is because of water evaporation. Appearance of the salt during heating | After 3 to 5 minutes, as water was evaporating and reaching its melting and boiling point, salt began to bubble. At the beginning of heating it was powdery solid then it changed to liquid and at last solid again. Volume of salt decreases because of lost of molecules. We waited for 10 minutes until it cooled down. | Calculations: Raw data collected Mass| Grams | Uncertainty /g ±0. 01| Crucible| 42. 20 g| 0. 02 %| Pure H2O | 1. 36 g| 0. 73 %| Pure CoCl2| 1. 66 g | 0. 60 %| | | Total uncertainty | | | 0. 08 %|
Find the masses: Crucible + CoCl2. H2O = 45. 23 g Anhydrous = 43. 86 g Mass of pure H2O = 45. 23 – 43. 28 = 1. 36 g Mass of pure CoCl2 = 3. 02 – 1. 36 = 1. 66 g Find the uncertainty: CoCl2 = 1. 66 = 0. 01 = 0. 60 % 100 x H2O = 1. 36 = 0. 01 = 0. 73 % 100 x Crucible = 42. 20 = 0. 01 = 0. 02 % 100 x Total uncertainty: 0. 02 % + 0. 60 % + 0. 73 % = 1. 3 % 100 = 1. 3 = 0. 08 % 6 x Find the percentage of water: % Water = weight of water in sample * 100 Original weight of sample % 45. 03 = 1. 36 *100 3. 02 Find the number of moles: CoCl2 . H2O CoCl2 H2O 1. 661. 36 1. 66 * 18 n = 1. 36 * 130 29. 88 n = 176. 8 g 130 18 n n = 176. 8 / 29. 88 n = 6 moles CoCl2 . 6H2O CoCl2 +6H2O Conclusion: From this experiment, I investigated that my hypothesis is fairly accurate as I predicted. Therefore it is concluded that through empirical formula, the degree of hydration is hydrated CoCl2 was determined to a relative degree of accuracy. It is determined to be approximately 6 moles of water bonded with 1 mole of CoCl2 and giving: CoCl2 . 6H2O. Evaluation:
Our experiment was fairly close as the ratio was 1:5. 9. However, the ratio achieved through this experiment was, while approximately accurate to the accepted literature value of 1: 6, not so precise tat this ratio could be assumed to anything greater or lesser than 1 significant figure. This anomaly can be explained by acknowledging some errors within the experimental process. While the determined degree of hydration was not perfect, and indeed to find the current rather elaborate ratio a degree of rounding was still required, it was still reasonably accurate. Some errors can be: 1.
Over heating of the hydrated cobalt chloride can result in burning the anhydrous compound of cobalt chloride, therefore contaminating it with oxygen and alerting the mass present in the crucible. This could lead to varying degrees of inaccuracy. 2. Base on the fact that cobalt chloride is hydrophilic means; it will absorb moisture from atmosphere. Therefore, the experiment should be conducted in a dry, well-aired lab to avoid as little absorption as possible. 3. In contrast to burning the anhydrous compound, the heating could have failed to completely remove all the water or revise it; it may over heated that also effect on the accuracy.
Improvements: There are several ways to improve this experiment. The key improvement to this experiment would probably be to decrease the intensity with which flame is applied to the crucible. This reduces the possibility to reduce overheating, and increase the period of time spent dehydrating the sample to ensure a slower, more through and less intense dehydration. Another improvement can be using a lab, which has the suitable location for this experiment. At last, have a expert partner or teacher to tell u, when stop heating the crucible can improve the accuracy of constant mass to achieve.
