Chem 1A 04 Lab 3 Hydrate Report PDF

Preview

Summary

Chem 1A Lab report for Lab 3 Hydrate Report for professor Woodbury. ...

Description

1

Professor Dr.Woodbury Chem 1A_04 4 April 2019 Lab Report 3: Hydrate

Introduction/ Background In the Hydrate lab at first, a sample of approximately 0.1000 grams of copper (II) sulfate pentahydrate was heated for the purpose to cause a chemical reaction that would remove all of the water molecules in order to determine the number of moles of water in the inorganic compound. Before the chemical reaction, the compound is a hydrated compound, a compound with a fixed amount of water molecules. The chemical reaction evaporates and removes the hydrate water molecules turning the blue exterior color of the compound to turn grayish-white. By removing this compound’s water molecules the hydrate can now be redefined as an anhydrous compound. As the water molecules and new anhydrous compound differ in mass that information can be converted from grams to moles by multiply by 1 mole over the compounds molar mass (g). By dividing each component by the lowest number of moles those calculations can then be used as whole numbers to construct the complete empirical formula. As the judgment call to assume all of the water molecules were actually in fact removed this process was repeated three times to learn new techniques on how to improve and to prevent random error. After perfecting the process with a known substance the chemical reaction was repeated twice with an

2

unknown substance to bring variety within elements proving this process works with other elements not only copper (II) sulfate pentahydrate. Procedure Initially, to remove the possible error from outside water molecules an empty crucible was heated repeatedly until the mass of the crucible became within 0.0010 grams of the previous weight after initially heating the crucible for 15 minutes over a Bunsen burner. After recording the initial the mass a sample of approximately 0.1000 grams of copper (II) sulfate pentahydrate was added into the crucible and measured as a hydrated compound. After recording the weight in grams the compound was heated over the Bunsen burner to become an anhydrous compound. After 10 minutes the compound was taken off the Bunsen burner and weighed after it returned to room temperature. The previous step was repeated twice to contain an anhydrous compound that was in a constant weight between its last two measurements. Following the task of collecting a constant weight was to discard the compound and repeat two more times. Following the completion of analyzing copper (II) sulfate pentahydrate, the process used previously was duplicated, however with two unknown elements.

3

Summary Data Table Summary Data table of Copper(II) Sulfate Pentahydrate Trial 1

Trial 2

Trial 3

Mass of empty micro-crucible (grams)

12.704

14.7364

14.6815

Mass of micro-crucible + hydrate (grams)

12.813

14.8241

14.7823

Mass of micro-crucible + anhydrous compound, First heating (grams)

12.771

14.7902

14.7472

Mass of micro-crucible + anhydrous compound, Second heating (grams)

12.7701

14.7879

14.7463

Summary Data Table of Unknown Hydrate Unknown #15 Unknown #1 Trial 1

Trial 2

Mass of empty micro-crucible (grams)

13.8808

13.6435

Mass of micro-crucible + hydrate (grams)

14.0287

13.7492

Mass of micro-crucible + anhydrous compound, First heating (grams)

13.9691

13.7131

4

Table of Results Table of Results of Copper(II) Sulfate Pentahydrate Trial 1

Trial 2

Trial 3

Mass of empty micro-crucible (grams)

12.704

14.7364

14.6815

Mass of micro-crucible + hydrate (grams)

12.813

14.8241

14.7823

0.109

0.0877

0.1008

12.7701

14.7879

14.7462

Mass of anhydrous compound (grams)

0.0661

0.0515

0.0647

Mass of water (grams)

0.0429

0.0362

0.0361

Moles of anhydrous compound (moles)

0.000414134

0.000322661

0.000405363

Moles of water (moles)

0.002381312

0.002009405

0.002003855

C uSO 4 + 6H 2O

C uSO 4 + 6H 2O

C uSO 4 + 5H 2O

1

1

1

5.750093595

6.227595879

4.943357305

Mass of hydrate (grams) Constant mass of micro-crucible + anhydrous compound (following final heating) (grams)

Formula of hydrated compound Ratio of anhydrous and water moles of anhydrous / moles of anhydrous moles of water / moles of anhydrous

5

Table of Results Assuming that the anhydrous compound is CaSO4 Trial 1 #15

Trial 2 #1

Mass of empty micro-crucible (grams)

13.8808

13.6435

Mass of micro-crucible + hydrate (grams)

14.0287

13.7492

0.1479

0.1057

13.9691

13.7131

Mass of anhydrous compound (grams)

0.0883

0.0696

Mass of water (grams)

0.0596

0.0361

Moles of anhydrous compound (moles)

0.000648597

0.000511238

Moles of water (moles)

0.003308303

0.002003855

C aSO 4 + 5H 2O

C aSO 4 + 4H 2O

1

1

5.10070593

3.919608512

Mass of hydrate (grams) Constant mass of micro-crucible + anhydrous compound (following final heating) (grams)

Formula of hydrated compound Ratio of anhydrous and water moles of anhydrous / moles of anhydrous moles of water / moles of anhydrous

Table of Results Assuming that the anhydrous compound is MgSO4 Trial 1 #15

Trial 2 #1

Mass of empty micro-crucible (grams)

13.8808

13.6435

Mass of micro-crucible + hydrate (grams)

14.0287

13.7492

0.1479

0.1057

13.9691

13.7131

Mass of anhydrous compound (grams)

0.0883

0.0696

Mass of water (grams)

0.0596

0.0361

Moles of anhydrous compound (moles)

0.000733596

0.000578236

Moles of water (moles)

0.003308303

0.002003855

Mass of hydrate (grams) Constant mass of micro-crucible + anhydrous compound (following final heating) (grams)

M gSO 4 + 5H 2 O

M gSO 4 + 3H 2 O

Formula of hydrated compound Ratio of anhydrous and water moles of anhydrous / moles of anhydrous moles of water / moles of anhydrous

1

1

4.509707433

3.465459072

6

C. Assume that the anhydrous compound is ZnSO4

Trial 1 #15

Trial 2 #1

Mass of empty micro-crucible (grams)

13.8808

13.6435

Mass of micro-crucible + hydrate (grams)

14.0287

13.7492

0.1479

0.1057

13.9691

13.7131

Mass of anhydrous compound (grams)

0.0883

0.0696

Mass of water (grams)

0.0596

0.0361

Moles of anhydrous compound (moles)

0.000546851

0.000431040

Moles of water (moles)

0.003308303

0.002003855

Mass of hydrate (grams) Constant mass of micro-crucible + anhydrous compound (following final heating) (grams)

Formula of hydrated compound

Z nSO 4 + 6H 2 O Z nSO 4 + 5H 2 O

Ratio of anhydrous and water moles of anhydrous / moles of anhydrous moles of water / moles of anhydrous

1

1

6.049735467

4.648884871

The identity of the unknown provided is:

Zinc sulfate (ZnSO4) from trial 1 #15

The formula of the hydrated unknown compound is:

ZnSO4 + 6H20

7

Discussion For experiment 1 as can be seen in Table, “Table of Results of Copper(II) Sulfate Pentahydrate ” section moles of water/moles of anhydrous for trial 1 through 3 all roughly had the same average number of moles, with values of 5.750 moles, 6.2275 moles, and 4.943 moles. With an overall average of 5.64 rounded up to the whole number 6, a number of moles for water in this hydrated compound are 6 with the experimental data the formula can be expressed as C uSO 4 + 6H 2 O . Even though 6 number of moles is incorrect, by the third trial the final calculated number of moles rounded out to 5 number of moles. Resulting in 5 number of moles makes the formula C uSO 4 + 5H 2 O , which is the correct formula for Copper(II) Sulfate Pentahydrate. The first trial can be assumed as near true value, but incorrect since the anhydrous compound was heated for too long, this statement can be determined by physically as the anhydrous appeared the color dark black - brownish after the heating process. Also, it can be proven by the calculation it was heated for too long, considering it has the largest “mass of water” burned off. Burned anhydrous could have been mistakenly assumed to be water evaporates into the air resulting in an error in the calculations of the number of moles of water in trial 1. In the second trial, the calculated mass of anhydrous was 0.051 grams. Comparing the second trial’s mass with trial’s one and three of 0.066 grams and 0.065 grams shows trial two had an extremely smaller mass. Having a low compared anhydrous mass suggest an error in the experiment since all the hydrates were weighted near the same mass. By reflecting on the process

8

in trial two, an error occurred by not heating the anhydrous long enough for all the water to evaporate. The probable reason this error occurred is that in trial one the anhydrous was burned since it was heated too long, therefore in trial two to prevent that mistake the duration of heating was greatly decreased. Lastly, in trial three, the number of moles/moles of anhydrous was 4.943 moles. Round this number up results in the correct formula for Copper(II)  Sulfate Pentahydrate at C uSO 4 + 5H 2 O . In trial three the experiment met the objectives of the lab, to find the number of moles of water in Copper(II)  Sulfate Pentahydrate. Success came from trial three because techniques on how to improve the lab resulted from extremely heating the anhydrous in trial one and barely heating the anhydrous in trial two. For part B of the lab, the objectives were to apply the techniques learned in part A in order to identify an unknown hydrate. The number of experimental moles of water in trial one was calculated to 6.04 moles of water. By calculating 6 moles of water we believe the unknown container number 15 in trial 1 of part B was Zinc sulfate heptahydrate. The reason the unknown is believe to believe Zinc sulfate heptahydrate is because out of Calcium sulfate dihydrate, Magnesium sulfate heptahydrate, and Zinc sulfate heptahydrate the unknown made a formula of Z nSO 4 + 6H 2 O which was closest to the actual formula of Z nSO 4 + 7H 2 O and was farther off then the other two formulas. For trial two of part B, forced by the limited time the unknown of container number 1 was not able to be identified as the ratios were completely off for all of the three given inorganic compounds. The major potential sources of error in this lab was a random error, the experimenter's inability to take the same measurement in exactly the same way to get exactly the same number. There are two situations within the lab where random error most likely

9

occurred. The first situation occurred with an inconsistent amount of time heating and cooling throughout the process. The next probable reason for the random error was because of weighting the compound with different weight machines constantly through the lab as there were a limited number of weights free to use under the time frame.

Post Lab Question

The identity of the unknown provided is:

Zinc sulfate (ZnSO4) from trial 1 #15

The formula of the hydrated unknown compound is:

ZnSO4 + 6H20...