Hydrated Compound Lab 704e1k

Honors Chemistry

Names: Aidan Marzo, Charmian Chan, Siddarth Bajpai Period 3 Date 3/11/2013

Hydrated Compound Lab

Purpose: To determine the formula of the hydrated CuSO4 by determining the number of water molecules that attach to a formula unit given a sample of the compound Procedure: 1. Mass both the crucible and the CuSO4 before heating 2. Place crucible containing the CuSO4 onto the ring stand above the Bunsen burner 3. Heat until all the color is gone and water is evaporated 4. Mass the CuSO4 after 5. Note the changes and write down the calculations to find the mass of the dehydrated CuSO4 Materials: · Ring stand · Bunsen burner · Clay triangle · Crucible · Sample of CuSO4 · Scale · Crucible tongs Data: Table 1: Masses of different objects before and after heating

Object

Mass

Crucible

16.721g

Crucible with salt

20.585g

Hydrated CuSO4

3.864g

Dehydrated CuSO4

1.959g

H20

1.905g

Observations: · Blue colored crystals · As heating progresses, color fades from the outside to the inside · Color fades from blue to light green and then to grey · Begins to slightly smoke before taken off the Bunsen burner

Calculations: CuSO4 1 mol of CuSO4= 63.55g Cu + 32.07 S + 64g O= 159.62g/mol CuSO4

1.959g CuSO4*(1 mol CuSO4/159.62g)= 0.0123 mol of CuSO4 H20 1 mol of H2O = 2.02g H +16g O=18.02g/mol of H2O 1.905g H2O*(1 mol H2O/18.02g)= 0.1057 mol of H2O Ratio 0.01057 mol H2O : 0.0123 mol CuSO4= 8.613 H2O: 1 CuSO4 Final Formula (Unrounded) : CuSO4 : 8.613H2O Final Formula (Rounded): CuSO4 : 9H2O’ Actual Ratio: CuSO4 : 5H2O Percent Error Formula (Approx. Value - Exact Value)/Exact Value * 100% Percent Error for Unrounded Ratio (8.613-5)/5 *100% = 72.26%

Percent Error for Rounded Ratio (9-5)/5 * 100% = 80.00%

Discussion Questions: Make sure to address the following questions in your discussion section: Would the error cause your ratio to increase or decrease?

1. What was the actual ratio you obtained (with all significant digits)? What was your rounded ratio to whole numbers? Is your actual ratio higher or lower than the rounded ratio? Research what the actual ratio should be. Is your answer too high or too low? What is the percent error? The actual ratio we obtained (with significant digits) was CuSO4 : 8.613H2O. The rounded ratio to whole numbers was CuSO4 : 9H20. Our actual ratio is lower than the rounded ratio. The actual ratio for a CuSO4 hydrate is CuSO4 : 5H2O The answer is much higher than the actual ratio due to some errors. The percentage error for the unrounded ratio is 72.26% while the percentage error for the rounded ratio is 80%. (Aidan) 2. How would your ratio change if you did not dehydrate the compound fully? If the compound had not been dehydrated fully, then there would still be excess water in the crucible. This would cause the mass of the dehydrated compound to be higher than it actually is. Therefore, underestimating the amount of water in the compound. This would also affect the calculations as the ratio would be smaller than it should have been. (Aidan) 3. Suppose some of the compound fell out of the test tube before heating but after massing. How would that change your ratio? This would increase the amount of estimated water in the compound. The water is calculated by taking the hydrated compound and subtracting that from the dehydrated compound. If some of the compound was lost after weighing it, this would increase the amount of water calculated. It would also change the estimated ratio of the hydrate and the H2O ratio would be higher. (Aidan) 4. How would your ratio change if the test tube was wet when the hydrated compound was added to it at the beginning of the experiment? This uned water would cause the mass of the hydrated compound to be greater, than it was in reality. When we heat the compound, the extra water would also evaporate leading us to believe that there was more water contained in the compound than there actually was. This would lead to an incorrect ratio with an increased number of water molecules. (Sid)

5. How would your ratio relate to another group’s who used the same compound, if you used 2.0 grams and they used 2.5grams? If the procedures were both done correctly and with minimal errors, the ratio should be the same. The ratio of water to Copper (II) Sulfate is the same regardless of the quantity of it. Both groups should end with the exact same ratios. (Sid)

6. Suggest what might happen if you left the anhydrous compound to sit overnight before weighing it for your data? Overnight, the anhydrous compound would presumably absorb water and hydrate itself. This would mislead the data in believing there was a smaller amount of water lost, leading to an incorrect number of water molecules in the final ratio. (Sid)

7. If you could improve this lab, what you do differently and why? Discuss at least three feasible improvements and why with reference to the other discussion questions and errors. (Note: relate this to #1 and the answers for the other questions).

1) To improve the lab and increase the validity of our data, we could have done the experiment twice, with different amounts (by mass) of the dehydrated compound. This would help make sure that the data was accurate. As the ratios are the same regardless of the mass, the ratios for each of the two trials would be the same. (Sid) 2. To improve the lab and increase the validity of our data, we should heat the crucible before adding the hydrated CuSO4. This way we can be 100% sure that there won’t be any excess water within the crucible. 3. This lab could be improved the compounds were heated a few more times. These extra heatings would ensure that all of the water had evaporated, giving us extremely accurate data. (Charmian) Reflection: Through this lab, we now understand the basics of hydrates and their composition. We now realize that some compounds include H2O molecules within them. By evaporating the water, we are given the dehydrated compound, called the anhydrous compound. We used our knowledge of empirical and molecular formulas to calculate the ratio of the H2O to the Copper (II) Sulfate. This knowledge has also added to our overall vocabulary of Chemistry. (Aidan)

Conclusion Statement: Write a one to two sentence statement to conclude what you did in your lab, what was your actual and how did it compare to your theoretical. In conclusion, we used the initial hydrated CuSO4 and evaporated all the water off to find the ratio of H20 to CuSO4. Overall our data had some errors as we came up with a 9:1 (Rounded) ratio rather than the actual ratio 5:1. (Aidan)