Investigating the formula of an unknown hydrate

3. Heat the uncovered crucible to drive off the water of hydration. Turn off the burner. Allow the crucible to cool completely. Measure the combined mass of the crucible and contents.

4. Repeat step 3 until the mass is constant

Controlling the variables:

• The same materials were used

.

• The same substance was used.

Safety:

• Always handle the crucible with crucible tongs.

• Tie back long hair when using Bunsen burner.

• Never leave a lighted burner unattended.

Data collection and processing

Table1 : Before heating

*The mass has an error of (±0.1) because of the reading in the mass, in which they show up to only 2 decimal points

Table2 : After heating

1. Without a doubt, I would have expected that the mass of the hydrated compound to fall down in the mass due to the water loss in the compound by evaporation.

2. Mass of anhydrous = 4.44g

Molar mass of anhydrous = 126.14gmol^-1    

                 

   

Number of moles = 4.44g                             =        0.0352 moles

                                   126.14gmol^-1                          

         3.             Mass of water = mass of hydrate (before heating) – mass of hydrate(after heating)

Mass of water = 7.45g – 4.32g =   3.13g

        4.  To determine the formula of the unknown hydrate, we do the following:

 Mass of water = 3.13g                                                Mass of anhydrous = 4.44g

Molar mass of water = 18.02gmol^-

                                   Molar mass of anhydrous =126.14gmol^-1                        

nH20   =  m           =   3.13        =    0.1737                   n anhydrous        =      m      = 4.44           = 0.0352                                                                                                         .               M                 18.02                                                                                  M     126.14

X = nH20                =        0.1737        =   4.94     ≈ 5                                                                                                                                                                                                             .     n anhydrous              0.0352          

Formula for the unknown hydrate is   n.5H20. Since the molar mass of the anhydrous is 126.14gmol^-1, then we can identify that the most certain compound to have this is Magnesium Sulphate. So the formula of the hydrate is  MgSO4.5H20, the name of this compound is Magnesium Sulphate Pentahydrate.

Conclusion

From the analysis of the results you can clearly see that the formula of the unknown hydrate turned out to be MgSO4.5H20. The fact that X being = to 4.94, shows how close it was to the nearest the whole number and in turn proves that the experiment was successful.  If we are to compare these results with the literature values, you can clearly see that the experiment did turn out right and that the formula MgSO4.5H20 is correct, for similar experiments carried out by scientist received the same results. However, if we are to compare these results to the results of other people in the class then there is a difference with a few of the groups. One group received 0 while one had 2. This is clearly due to the sources of errors that may have occurred in their experiments.

The possible sources off error in this experiment may include:

• An appropiate amount of the unknown hydrate may have not been used.
• It wasnt left on the heater for enough time to allow complete water loss.
• Material used may have been tampered with and so would affect the overall results.
• Wrong measurements were taken.

Although my experiment was successful, many improvement could have been made to both my experiment and too the experiment. This includes:

• Repeating the measurements for more trials so that more accurate answers could be found.
• Using an accurate method to measure the mass, so as to reduce the errors in the experiment.
• Make sure that none of the compound is accidentally spilled out.