Analía Bellizzi – Chemistry Classes

Ronald Reagan Senior High School

Percent Composition of a Hydrate Lab

Percent Composition of a Hydrate

word document

Introduction

In this experiment, you will be heating a hydrate of copper (II) sulfate (CuSO4•nH2O) to evaporate the water. Masses are measured before heating to determine the mass of the original sample (the hydrate) and after heating to determine the mass of copper (II) sulfate (CuSO4) anhydrous. The difference between these two masses is equal to the mass of the water lost. Heating time and temperature are critically important for this experiment. If not enough heat is applied, some water will remain attached to the copper sulfate producing a low calculated mass percent water for the hydrate.

The pentahydrate is 100% isolable only in temperatures lower than 30 °C. The light blue trihydrate non-isolable form can be obtained around 30°C. White monohydrate form is available at 110°C, while the anhydrous form can be isolated near 250°C. If too much heat is applied, the anhydrous copper (II) sulfate (CuSO4), which has a grayish white color, decomposition starts at 250 degrees, while complete decomposition occurs around 600 degrees…

The reaction for the decomposition is as follows:

CuSO4 •5H2O(s)==> SO2(g) + CuO(s)+ 5H2O

Purpose:
  1. Determine the percent of water present in a hydrated copper (II) sulfate (CuSO4 • n H2O) and Epson Salts
  2. Calculate the value of  “n”, the number of  moles of water molecules present per mole of CuSO4  and Epson Salts

Materials: – for Part I and Part II

  • Hot plate
  • glass beaker
  • glass rod
  • ceramic pad
  • beaker tongs
  • Balance (at least 2 decimals)
  • Copper sulfate sample (2.5 to 3.5 g)
  • Epson Salt (Magnesium Sulfate Sample (Around 5.0 g)

Procedure: Part I

  1. Turn on your hot plate.
  2. Be sure your beaker and glass rod does not have any crack, and that that they are clean and dry.
  3. Measure the mass of the empty beaker with the glass rod inside.
  4.  Record this value in your data table with the maximum available precision.
  5. Obtain about 2.5 to 3.5 g of CuSO4●nH2O in your beaker and weigh it, together with the glass rod. Record this value in your data table with the maximum available precision.
  6. Calculate the mass of the CuSO4●nH2O by difference between your second and your first measurement.
  7. Place your beaker with the sample and the rod on the hot plate.
  8. Heat the compound gently Note the release of any steam from the beaker.
  9. Continue heating gently until the salt turns completely light grey. Be careful not to overheat! The heat can become so intense that the sulfate in the salt begins to break down. If this happens the salt will turn yellow and produce a sulfurous smell. It will also ruin your data since it will reduce the mass more than expected due to the decomposition of the salt.
  10. Use the glass rod to stir the chemical to avoid overheating in some areas. Use the glass end to stir the compound.
  11. Stop heating when the salt has lost all traces of blue color. If the compound turn yellow, remove it from the hot plate and place it on a ceramic pad (DO NOT PLACE THE HOT BEAKER ON THE COOL TABLE, IT CAN SHATTER) Allow the beaker and its contents to cool completely.
  12. Once the beaker is cool, measure the mass of the beaker, the anhydrous salt and the glass rod.
  13. Heat the contents again for a short time (3 minutes). Then allow it to cool and weigh it. If the mass is the same as the previous weighing, then the salt has been completely dehydrated. If not, repeat the heating/cooling/weighing process until two successive weighing have the same mass.
  14. Record the final mass of the anhydrous salt in you lab notebook and do the calculations to show that the molar ratio of water to anhydrous salt really is 5:1.
  15. Empty the anhydrous salt onto a large watch glass. Use the dropper to add a very little water to the anhydrous copper (II) sulfate.
  16. Describe what happens in your lab notebook. For your report explain what is happening at the molecular level when you add water.
  17. When you finished this part of the lab empty all the CuSO4 into the beaker provided by your instructor for this purpose.

PART 1 PICTURES AND VIDEOS

Procedure: Part II

In this part of the lab you will repeat the same procedure performed for the salt of known formula with a salt for which you do not know the hydrate formula. The salt is magnesium sulfate – MgSO4 and, the same as Copper sulfate, it exists as a hydrate, but in this case we will find the amount of water surrounding the compound. (MgSO4●XH2O).
Use a minimum of 2 g. This will help to reduce errors due to small lab balance inaccuracies.
An additional challenge is that both the hydrate and anhydrous salt are white.
Finally, unless you frequently stir the crystals they will combine and harden, possibly trapping water inside To prevent stir continuously. You can use a metallic spatula this time. If clumps are formed, just continue stirring and heating until you see

PART II PICTURES AND VIDEOS

 Lab Setup

Your LAB SETUP should be a sketch of the picture on the right. 

LABEL every instrument or lab equipment. 

Before

After

Data Table Lab #1 with digital balance

Mass of  CuSO4●5H2O

Final mass of Anhydrous CuSO4 (without water)

Moles of CuSO4 in the anhydrous mass (mass / 159.5)

Mass of water

Moles of water (mass of water / 18)

Ratio between  moles of water /moles of anhydrous copper sulfate

 

Write down the formula of the hydrate  →

measurements

…………………g

…………………g

…………………mol

…………………g

…………………mol

………/………..

 

 

 

Data Table Lab #2 with digital balance

Mass of  MgSO4●XH2O

Final mass of Anhydrous MgSO4 (without water)

Moles of MgSO4 in the anhydrous mass (mass / 120)

Mass of water

Moles of water (mass of water / 18)

Ratio between  moles of water /moles of anhydrous Magnesium sulfate

 

Write down the formula of the hydrate  →

measurements

…………………g

…………………g

…………………mol

…………………g

…………………mol

………/………..

 

 

 

THIS DATA TABLE IS NOT FOR 2020-2021 STUDENTS

Data Table Lab #1 with triple beam balance

Mass of empty beaker + Glass rod        

Mass of beaker + glass rod + CuSO4●5H2O

Mass after heating (First time) beaker + glass rod + CuSO4●5H2O      

Mass after heating (Second time) beaker + glass rod + CuSO4●5H2O

Final mass of Anhydrous CuSO4 (without water)

Moles of CuSO4 in the anhydrous mass (mass / 159.5)

Mass of water

(Mass of beaker + glass rod + CuSO4●5H2O – Mass after heating (Second time)

beaker + glass rod + CuSO4●5H2O)

Moles of water (mass of water / 18)

Ratio between  moles of water /moles of anhydrous copper sulfate

 

Write down the formula of the hydrate  →

measurements

…………………g

…………………g

…………………g

…………………g

…………………g

…………………mol

…………………g

…………………g

…………………g

…………………mol

………/………..

 

 

 

THIS DATA TABLE IS NOT FOR 2020-2021 STUDENTS

Data Table Lab #2 with triple beam balance

Mass of empty beaker + Glass rod        

Mass of beaker + glass rod + MgSO4●XH2O

Mass after heating (First time) beaker + glass rod + mGSO4    

Mass after heating (Second time) beaker + glass rod + mGSO4

Final mass of Anhydrous MgSO4 (without water-Lowest number you got)

Moles of MgSO4 in the anhydrous mass (mass / 159.5)

Mass of water

(Mass of beaker + glass rod + MgSO4●5H2O – Mass after heating (Second time)

beaker + glass rod + MgSO4●5H2O)

Moles of water (mass of water / 18)

Ratio between  moles of water /moles of anhydrous copper sulfate

Write down the formula of the hydrate  →

measurements

…………………g

…………………g

…………………g

…………………g

…………………g

…………………mol

…………………g

…………………g

…………………g

…………………mol

………/………..

 

 

 

Observations Part 1

  1. Describe the Copper (II) sulfate hydrate before heating
  2. Describe the changes you can observe during the heating process.
  3. Describe the way the anhydrous compound looks like. 

Observations Part 2

  1. Describe the magnesium sulfate hydrate before heating
  2. Describe the changes you can observe during the heating process.
  3. Describe the way the anhydrous compound looks like. 

Analysis Questions

  1. How many moles of copper (II) sulfate (CuSO4) did you have in your original sample?
  2. How many moles of water did you have in your original sample? 
  3.  Examine the formula for the hydrate: CuSO4 • nH2O. Notice that “n” is “the molar ratio of water to copper sulfate.” Find the numerical value for n in this sample (use your numbers from part a above). 
  4. The actual mass percent of water in the hydrated copper (II) sulfate compound should have been 36.1%. Compare this value to the experimental percentage you obtained. 
  5. In the experiment involving hydrated copper sulfate, overheating causes a high calculated percent value for water.
    1. Why is the high reading obtained? Hint: Overheating causes copper (II) sulfate, CuSO4 to turn into copper (II) sulfide, CuS. 
    2. What is lost from the CuSO4 in this process?
  6. Where does it go?
  7. What experimental evidence would you have to indicate you inadvertently overheated the hydrated copper sulfate compound? Hint: Re-read the “Experimental Considerations” section.
  8. Determine the mass percent of each element present in CaCO3.
  9. Determine the number of grams of Na present in 4.0g of NaOH.
  10. Calculate the mass percent water in MgSO4 • 2 H2O

Your lab report should have the following parts:

  • date
  • names of members in the group
  • Title
  • purpose
  • materials
  • procedures
  • lab setup
  • data tables
  • calculations
  • observations
  • analysis questions

=============================

VERY IMPORTANT

  • Failing to complete ALL exercises or questions will result in an “I” (incomplete) which is equivalent to an “F”
  • Everything  MUST be written in pen (Blue or black only)
  • NO TYPED WORK WILL BE ACCEPTED
  • Graphs & Charts MUST BE AS FOLLOWS:
    • In graph paper.
    • with LABELLED AXES AND UNITS using ruler.
    • They must be pasted on the homework page or lab report using only tape or glue (NO STAPLED GRAPHS WILL BE ACCEPTED)
      Any LAB SETUP DIAGRAM showing a process must be done in COPY PAPER and PASTED into the lab report.