Hydrates Lab Report Final - Chemistry Exp: Explore And Evaluate Bonding Properties Hydrates PDF

Preview

Summary

Hydrates Lab Report...

Description

Introduction

The purpose of this experiment was to explore and evaluate the bonding properties and characteristics of hydrates. The 4 main objectives discussed are (1) Explore the characteristics (2) Find the percentage of water is various hydrates, (3) Determine if dehydration is a reversible or irreversible change, and (4) Determine the mathematical relationship between starting mass and mass lost (1). The definition of a hydrate is a chemical that contains one or more water molecules as part of their crystalline structure. A an-hydrate is a hydrate without the water compound (2). This lab explored hydrates and the 4 objectives in a three procedure process through observation, experimentation, and mathematical methods to help prove whether dehydration of a hydrate is reversible or not. This is significant in the food industry for a number of different uses.

Procedures and Observations

Equipment and materials used in one or more procedure included: Hydrated copper sulfate (CuSO4), hydrated ferrous sulfate, hydrated cobalt sulfate, sucrose, epson salt, 4 test tubes, test tube rack and holder, ring stand, crumble and lid, iron ring, porcelain triangle, bunsen burner and striker, water bottle, magnifying glass, eye dropper, and digital scale. The magnifying glass was cracked and unusable. This was a three procedure experiment and data was collected from both observation and experimentation. Mathematics was used to explore water composition lost, conservation of mass and the reversibility properties in question. Error results and analysis included. The first procedure (Part 1) used heat to dehydrate the 4 hydrates and sucrose. In this part, peasized samples (1-3g) were place separately in test tubes and heated for approximately 1 minute

over the bunsen burner. After the samples cooled, each were tested to see if they experienced a reversible or irreversible reaction to the heat. See Table A for specific data and results. Each hydrate and the sucrose had a reaction when heat was applied and the following was observed and recorded. The first sample tested was the hydrated ferrous sulfate. Ferrous appeared bright blue/indigo in color and slightly thick crystalized particles with part of the small sample clumped, not uniform in texture. The reaction was immediate when heat was applied. Ferrous sulfate melted, bubbled, and evaporated which created a layer of condensation inside the test tube. As the reaction took place, the bright blue color of the ferrous sulfate started to fade and turned into a lighter blue. Then dulled into a white yellowish color when finished. After the sample cooled, water was added to the dehydrated ferrous and the color started to return to it’s original state. The hydrated cobalt sulfate, had a similar reaction although the appearance and texture differed. Hydrated cobalt sulfate in its preheated state is dark purple or violet in color, with a fine powder crystalline texture and slight clumped together in the sample collected. When heat was applied, cobalt reacted quickly. It bubbled and melted together, then popped, hissed as the water began to condensate and coat the upper inside of the test tube glass. A darker, deeper violet color started to form and with the small specs of bright blue floated at the surface of the now darker substance. Once the cobalt seemed to be in its an-hydrate state and cooled, the rehydration process started to take place. The transformation took about 10-15 seconds for the an-hydrate darker substance to start to return to its original hydrate color and state. The hydrated copper sulfate (CuSO4), which is the focus in the next procedure, had a different result after being dehydrated. The color changed during the dehydration process transitioning from a light blue-green to a very light green, almost white substance. The transformation seemed to

take place more around the edges where the test tube was generating the most heat. The texture stayed the same, but popping, sizzling and evaporation was observed. When water was reapplied to attempt to rehydrate (2-3 drops), it was found through observation, that the water molecules did not re-bond with the copper sulfate. The dehydration process was found to be irreversible. Was there bond that weak? Finally, sucrose was heated, observed, cooled, and then applied 3 drops of water. The sucrose sample looked like small uniform white crystalline particles but when heat was applied, quickly melted together in a gooey homogeneous mixture. When water was added after cooling, it pooled on top of the now hard substance. The second procedure conducted included 3 individual samples (1-3g) of hydrated copper sulfate (CuSO4). Multiple samples allow for accuracy and precision. Each sample was collected and placed in the pre-weighed crucible and weighed the pre-heated hydrates for mass in grams. The crucible was placed above the heat from the bunsen burner (approx. 6”) on the iron ring and stand provided. A timer was set during each trial. Each sample was heated for approximately 10 minutes. After each sample was heated until color had faded to a dull whiteish color, the CuSO 4 samples were weighed for a second time. These results are noted in Table B along with 2 additional sample results from group B and C. It is assumed that group B and C followed the same directions with similar erroneous factors. Finally, the mass of water is calculated for each sample of hydrated copper sulfate (including Group B and C) as well as the actual mass percentage of the hydrated copper sulfate. The third procedure was similar to part 1 but with epson salt. The epson salt appeared bright white in color with slightly clumped, crystalline textured particles. A pea-sized sample of epson salt was placed in a test tube and heated over the bunsen burner for approximately 1 minute. The reaction of the epson salt to the heat was immediate. Popping and slight hissing sounds were

heard and shortly into heating, the crystalline nature of the epson salt started to break down turning into a fine powder substance and turned an-hydrate. When water was applied, it pooled on top and refused to bind. It did not return to its original state. (thus proving epson salt is a irreversible hydrate.)

Data

The date tables and graph represent the three part experiment. Part 1 observations were recorded in Figure 1a, 1b, 1c and 1d and represent the hydrates (and sucrose) observations before, during and after heat. Figure 2 featured the hydrated copper sulfate experiment data along with the data from two other groups from part 2. Figure 3 used the data from Figure 2 to show the relationship of the an-hydrated copper sulfate to water lost (or the mass of water). Figure 4 included the epson salt observation data found in part 3.

Figure 1a - Hydrated Copper Sulfate (CuSO4*5H2O) to An-hydrated Copper Sulfate (CuSO4) Appearance

Copper

Before Heat During Heat After Heat Water Added

Figure 1b - Hydrated Ferrous Sulfate to An-hydrated Ferrous Sulfate

Appearance

Ferrous

Before Heat During Heat After Heat Water Added

Figure 1c- Hydrated Cobalt Sulfate to An-hydrated Cobalt Sulfate Appearance

Cobalt

Before Heat During Heat After Heat Water Added

Appearance

Sucrose

Before Heat During Heat After Heat Water Added Figure 1d - Sucrose (Sugar) to Sucrose - Water *Figure 1a-1d shows relevant observation data for Sucrose and the hydrated Copper, Ferrous, and Cobalt Sulfates, before, during, and after heat added

Mass of H2O Lost versus Initial Sample Mass

1.63g

Mass of H2O Lost

1.3g

Figure 20.98g - Mass of Hydrated Copper Sulfate before and after heat Before Heat

Sample 1

Sample 2

Sample 3

Sample 4 (Group B)

Sample 5 (Group C)

Mass of Crucible

32.91g

32.91g

37.29g

18.84g

38.74g

0.33g Mass of Crucible & Sample

34.11g

34.45g

40.73g

21.17g

39.91g

2.33g

1.17g

0.65g

0g

Mass of 1.21g 1.17g (CuSO4)

1.54g

1.21g

3.437g

1.54g

2.33g

3.44g

Mass of Sample Before Heat After Heat

Sample 1

Sample 2

Sample 3

Sample 4

Sample 5

Mass of Crucible

32.91g

32.91g

37.293g

18.84g

38.74g

Mass of Crucible & Sample

33.68g

33.88g

39.49g

20.33g

39.47g

Mass of (CuSO4)

.77g

.97g

2.19g

1.49g

.73g

Mass of H2O Lost

0.43g

.57g

1.24g

.84g

.44g

Mass % of H2O in each sample

35.5%

37.0%

36.0%

37.6%

36.1%

*Includes Mass of H2O lost to evaporation and Mass % of H2O in each sample *To find Mass of for CuSO4, Mass of Crucible and Sample was subtracted from Mass of crucible *Sample 4 and 5 are sets from 2 other groups

*Masses measured in grams with data from Figure 3 using mass of sample before heat for the an-hydrated copper sulfate mass and mass of H2O lost for the mass of water *There is a direct correlation between the sample mass and the mass of water; as sample mass increased water mass lost increased

*Slope is the mass % of H2O

Figure 4 - Epson Salt Observation Results Appearance

Epson Salt (MgSO4)

Before Heat

Clumpy, bright white, crystalline texture

During Heat

Clumps collapsed, evaporation then condensation, salt popped and hissed

After Heat

Crystalline texture turned into a fine white powder, shrunk or dissipated in size

Water Added

Pooled on top of the now hard, an-hydrate compound, white in color but caked to test-tube

*Figure 4 shows the observed transformation of Epson Salt before and after heat is applied **This test was attempted 2 times and Epson salt did not show to be water soluble after water was removed via heat

Data Analysis and Calculations

This experiment provided strong data to support which molecular bonds are strong and weak. The hydrates showed a stronger bond than the sugar or epson salt with H2O. But what about copper sulfate? During the initial procedure, it was verified that not all hydrates experience reversibility properties. The hydrated ferrous sulfate and hydrated cobalt sulfate showed color change during the dehydration process and returned to their original colors after water was reintroduced. Both were found to reversible. Unlike ferrous and cobalt, the hydrated copper sulfate

changed in color when the water was removed and when water added back to the an-hydrate, the color remained and the water refused to re-bond. Therefore it can be concluded that copper sulfate is has an irreversible change. This lead to ask the question, why do some hydrates have a stronger molecular bond to H2O than others? Epson Salt also showed a irreversible change. When the salt went through the dehydration process, it hardened and caked to the inside of the test tube. Unlike, the hydrates, color change was not a factor. This made it hard to identify when the process was finished. When water was reintroduced, there was no bond with the water. Does type of molecular bond depend the type of compound and total water content or solubility? In the second procedure, copper sulfate was explored in-depth and helped to define how much and how long water molecules take to completely evaporate. It is important to note conservation of mass. A compound doesn’t lose mass but is altered when a reaction takes place. Mass stays the same in theory, but the separated compound(s) go somewhere else. This report will expand in the conclusion section. To find the amount of water lost, data in Figure 2 was used to find the mass % of water in each sample. Here mathematics was applied and the following calculation was used: Mass of H2O lost /Mass of Sample b/f heat X 100 = Mass % of H2O which was recorded in the final row. The results showed consistency but did not discount for error and will be discussed in the conclusion section of this report. When calculating the actual mass % of water in hydrated copper sulfate, it was found that: Real Mass % of H2O in CuSO4 X 5H2O Cu = 63.55g S = 32.06g O = 16.00g H = 1.008g H2O = 2.016g+16g (H = 2g; O = 8.02g) CuSO4 X 5H2O = 63.55 g +32.06 g+(16∗4)+(18.02∗5)=249.03 g /mo l

Using (18*5)/249.03g, the amount of H2O in CuSO4*5H2O is 36.1% The error % of the average water mass lost in all collected samples of copper sulfate was found by %error actual - %error sample / %error actual .361-.364/.361 = .00831 X 100= .831% error

Conclusion

This lab exercise explored the bonding properties and characteristics of hydrates. It became evident that reversibility depends on the strength of the molecular bond to hold water molecules to the compound. This experiment provided strong data to support which molecular bonds are strong and weak. The hydrates showed a stronger bond than the sugar or epson salt due to their covalent bond with H2O. Although the hydrated copper sulfate showed molecular weakness when tested.

References (1) Lab Manual (2)...