Hydrate Formula

Kesean Williams

Brantley Miller

Pd. 11

1/11/16

Determination of a Formula for a Hydrate

Introduction

The focus of the experiment will be a hydrate of copper (Ⅱ) sulfate (CuSO4 ᐧ5H2O) The object of this experiment will be to find the experimental formula for the hydrate of CuSO4 by heating the crystal to dryness. The success of the lab will be determined by how accurate the experimental formula is compared to the actual formula.

Theory

If heat is applied to Copper (Ⅱ) sulfate pentahydrate, then the experimental form will be equivalent to the theoretical formula. Important key data that will be needed to achieve the goal of the lab experiments includes the initial mass of hydrated crystal, the final mass of anhydrous crystal, the

mass of water driven off, molar mass of water, the molar mass of Copper (Ⅱ) sulfate pentahydrate, the moles of water driven off, the moles of anhydrous crystal, the mole ratio of H2O to Copper (Ⅱ) sulfate pentahydrate, the experimental formula of the hydrated crystal, the theoretical formula of the hydrated crystal, and the percent error.

Hydrates are ionic compounds--also termed as salts--with a definite amount of water that is part of their structure. The water is not part of the chemical substance, a fact that is represented in the way the chemical formula is written. Take magnesium sulfate monohydrate (MgSO4 H2O) for example: The numerical prefix preceding hydrate represents the amount of water in the hydrate; in this case there would be one water molecule for every molecule of MgSO4. Another example would be Copper (Ⅱ) sulfate pentahydrate (CuSO4 5H2O) for example: Again, the numerical prefix preceding hydrate is indicative of the amount of water in the hydrate; in this case there would be five water molecules for every molecule of CuSO4.

Before continuing, the difference between hydrates and anhydrous salts must be stressed. They should never be mistaken to be one and the same. This is because unlike anhydrous salts, hydrates contain water in their chemical formulas. Anhydrous salts can even be differentiated from regular table salt--anhydrous salts contain absolutely no water at all. Anhydrous salts are used by glass, chemical, and paper manufacturers to remove organic liquids and similar impurities.

This method is not exclusive to this experiment; it has real-world applications as well. The method of heating to a constant mass is implemented by paper makers, who remove non-paper particles through the use of heat and a salt mixture

Materials

•Balance

•Crucible Tongs

•Spoon

•Bunsen Burner

•CuSO4, Hydrated

•Stirring Rod

•Ceramic Fiber Square

•Distilled Water Bottle

•Weighing Paper

•Clay Triangle

•Iron Ring

•Crucible and Lid

•Ring Stand

Procedure

1.The crucible and lid were heated to dryness, the burner was turned off, and the crucible and lid were placed on the fiber square to cool.

2.The mass of the crucible and lid were recorded.

3.About 1.5 g. grams of hydrated Copper (Ⅱ) sulfate pentahydrate were measured out and and added to the crucible. The new mass was then recorded.

4.Observations of the hydrate were made and recorded.

5.The crucible was placed on the triangle and the cover was positioned in the suggested manner. The crucible was then heated for a total of 5 minutes.

6.The crucible was set on the fiber square to cool, and then the masses of the crucible, lid, and anhydrous salt were taken.

7.The crucible and contents were put back on the clay triangle and heated for another five minutes. It was allowed to cool and then the mass was taken and recorded.

8.The mass after the final heating was taken and recorded as the final mass of the crucible and contents.

9.Observations of the crystal were made and recorded.

10.A distilled water bottle was used to put a few drops of distilled water on the anhydrous salt and observations were recorded.

11.The anhydrous salt was safely disposed of in the trashcan, and all used instruments and materials were cleaned and returned to their proper areas.

Data

Table 1

Observations of crystal before heating

Blue crystal; solid; mostly small crystals

Observations of crystal after heating to a constant mass

White; some small flakes, some large; general shape retained

Observations of crystal after adding water

Teal color, “sizzle” sound heard when adding water; same shape

Table 2

Mass of Empty Crucible and Lid

29.45g

Initial Mass of Crystal, Crucible and Lid

30.96g

Mass of Crystal, Crucible, and Lid After First Heating

30.36g

Mass of Crystal, Crucible, and Lid After Second Heating

30.35g

Constant mass of Crystal, Crucible, and Lid

30.35g

Theoretical Formula of Hydrated Crystal

CuSO4ᐧ5H2O

Calculations:

1.Initial Mass of Hydrated Crystal

Initial mass of crystal, crucible, and lid

-Mass of empty crucible and lid 30.96-29.45=1.51g

2.Final Mass of Hydrated Crystal

Constant Mass of Crystal, Crucible, and Lid

-Mass of empty crucible and lid 30.35-29.45=0.90g

3.Mass of Water Driven off

Initial Mass of Hydrated Crystal

-Final Mass of Hydrated Crystal 1.51-0.90=0.61g

4.Molar Mass of Water

2(Mass of Hydrogen)

+1(Mass of Oxygen) 2(1.01)+1(16)=18.02g

5.Moles of Water Driven off

.61g1x 1 mol18.02gH=.034 moles

6.Molar Mass of CuSO4

1(Mass of Cu)+1(Mass of S)+4(Mass of O) 63.55+32.07+64=159.62 moles

7.Moles of Anhydrous Crystal

.90gCuSO4x1 mole159.62=.0056 moles

8.Mole Ratio of H2O to CuSO4

Moles of H2O Driven off:Moles of Anhydrous Crystal .034 moles:.0056 moles

6.1moles:1 mole

9.Experimental Formula of the Hydrated Crystal CuSO4ᐧ6.1H2O

10.Percent Error

I Theoretical-Experimental I x 100

Theoretical 5-6.15x100=22%

Conclusion:

The objective of the lab was met successfully, with the creation of a formula that had only a 22% chance of inaccuracy. Caution was used when handling samples, to allow for minimum effect on results. Procedure was followed carefully without the slightest deviation. Astute questions were asked, such as those regarding certain calculations, and the use of significant figures. All data was recorded efficiently and accurately. Samples were studied very carefully before making qualitative observations. The Bunsen burner was always operated at the appropriate level. All aspects of the lab were taken seriously.

The initial mass of hydrated crystal was determined to be 1.51 grams.

This piece of data was used to find the mass of water driven off. In order to find the mass of water driven off, another value--the final mass of anhydrous crystal, was subtracted from the initial mass of hydrated crystal. This value was found to be .90 grams. The mass of water driven off was determined to be .61 grams. The molar mass of water, which is 18.02 grams, was used together with the mass in grams of water driven off to find the moles of water driven off. The moles of water driven off was calculated to be.034 moles. This value was a crucial half of the experimental formula, and thus crucial to the lab. The final mass of anhydrous crystal was used together with the molar mass of CuSO4 to find the moles of anhydrous crystal. The molar mass of CuSO4 was found by using the periodic table to find the total mass in grams of one copper atom, one sulfur atom, and four oxygen atoms. The moles of anhydrous crystal was determined to be .0056 moles. This was the other crucial half of the experimental formula, thusly crucial to the lab. The experimental mole ratio of H2O CuSO4 was found to be 6.1:1. This information was used to find the experimental formula of the hydrated crystal. The experimental formula was found to be CuSO4 6.1H2O. This formula was compared to the theoretical formula in order to derive the percent error. The percent error was calculated to be 22%. This crucial value was what described how successful the experiment ultimately

was.

Possible sources of error would include firstly, a small degree of contact with the sources. This would likely be the least significant of all sources, due to the level of care exhibited throughout the experiment. Secondly, the sample could have unintentionally been over or underheated. Depending on which, the flame might have been weak enough that all of the water might have not have burned away, or so strong that some portions of the crystal may have started to burn away. A final possible source of error would be calculations that were executed with imperfections such as transposed digits, or erroneous starting data. Either of these could have had devastating effects on the outcome of the experiment.