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Composition Of Hydrates Lab Conclusion Essay


In this lab, our purpose was to calculate the value of X in the chemical equation CuSO4 ∙ XH2O using our knowledge of percent composition. The only information we were given was that the value of X is somewhere between one and ten which indicates the number of water molecules there are that hydrate the copper (II) sulfate solid.

To solve this problem, our group was to find the mass of the hydrated solid and then compare it to the mass of the anhydrous solid to figure out the percent composition of water in the CuSO4 ∙ XH2O which will eventually lead to the number of moles represented by X in the chemical equation.


It is predicted that the mass of the hydrated copper (II) sulfate will be greater than the mass of the anhydrous copper (II) sulfate simply because a hydrated substance contains water while the anhydrous substance does not. At this time, it is not possible to predict the number of moles it takes to hydrate the copper (II) sulfate because we do not have the mass of the hydrated and anhydrous substance.



  • Hot plate
  • Crucible tongs
  • Digital balances
  • Testing paper
  • Crucible
  • Hot hands
  • Goggles
  • Apron
  • Sample of CuSO4 ∙ XH2O
  • Scoopula


  1. Put on safety equipment (goggles and apron).
  2. Acquire materials listed in the materials section.
  3. Using the electronic balance, measure the mass of the crucible. Then set it to zero.
  4. Place the substance into the crucible and measure the mass of the chemical. Record your observations of the mass.
  5. Place the crucible with it’s contents on top of the hot plate.
  6. Heat the CuSO4 ∙ XH2O on high until there is a visible change in colour. Record any observations. Make sure to use the testing paper to identify if water vapour is being released.
  7. Once the change has occurred, remove the crucible using the hot hands/crucible tongs.
  8. Turn off the hot plate.
  9. After the crucible has cooled, check the mass of the substance once again using the electronic balance.
  10. Clean up work space and return materials back to original locations.

*Note: The hot plate can burn you. Pay attention to what you are doing. If you burn yourself, immediately run your hands under cold water and inform your teacher of what happened.

Materials used in this lab may shatter if placed under heat. Also, remember not to remove your safety equipment consisting of goggles and apron until your teacher tells you to do so.


Hydrated Copper

(II) Sulfate Appearance

Mass of Hydrated Copper (II) SulfateAnhydrous Copper

(II) Sulfate Appearance

Mass of Anhydrous Copper (II) Sulfate
The substance was a blue colour.1.6gThe substance was a dull, white colour.1.2g


Table 1: Observations of the CuSO4 ∙ XH2O were recorded before and after removing the water by heating the substance. The mass of the substances was taken using an electronic balance. To check if water was evaporating when we heated the substance, we used the testing paper to check for water vapour. The paper turned pink indicating that we were dehydrating the substance by release the water.



Part of SubstanceMass (g)Percent Comp.Molar MassNumber of Moles“Cleaning up”Ratio










ElementPercent Composition
Copper (Cu)35.78%
Sulfur (S)18.05%
Oxygen (O)45.04%
Hydrogen (H)1.13%


Table 2 & 3: To figure out the mass of the CuSO4 and H2O, we looked at the mass of the hydrated and anhydrous versions of copper (II) sulfate and noticed a difference of 0.4 between 1.6 and 1.2 which indicated that the mass of the water was 0.4g while that mass of copper (II) sulfate was 1.2g. To calculate the percent composition, we took the mass of each part of the substance and divided it by the total mass. This concluded that 75% of the substance was copper (II) sulfate while 25% was water. To calculate the molar mass, we added up each element’s atomic mass for each part of the substance. By doing this, it figured out that the molar mass for copper (II) sulfate is 159.61 g/mol, while the molar mass for water is 18.0153 g/mol. To calculate the number of moles we used the formula triangle. For the two parts of the substance we took the mass and divided it by the molar mass to find out that there were 0.00725 mol of copper (II) sulfate while there were 0.022203 mol of water. To “clean up” we divided each of the number of moles by the lowest number which was 0.022203 (water). This resulted in the ratio of copper (II) sulfate to water being 1:3. In table 3, we calculated the percent composition of each specific element by taking the mass of the element and dividing it by the total mass of the compound and multiplying it by 100.



,rea +p any lar(e crystals before placin( them in the cr+cible. *etermine the mass of the coered cr+cible and crystals to the nearest $.$1 ( and record the mass in the data table.


Place the cr+cible -ith the copper s+lfate hydrate on the trian(le and a(ain  position the coer so there is only a small openin(. 2f the openin( is too lar(e thecrystals may spatter as they are heated. Heat the cr+cible ery (ently on a lo- flame to aoid spatterin(. 2ncrease the temperat+re (rad+ally for " or  min. and then heat +ntil the cr+cible (lo-s red for at least ! min. ,e ery caref+l not to raise the temperat+re of the cr+cible and its contents too s+ddenly. A color chan(e -ill occ+r -hich is normal b+t if the s+bstance remains yello- after coolin( it -as oerheated and has be(+n to decompose. Remoe the cr+cible from the flame and allo- it and its contents 3

!ake sure the crucible is covered$

to cool for ! min and then meas+re the mass. Record the mass in yo+r data table.


Heat the cr+cible and contents -ith the coer positioned as in step ! and contents to redness a(ain for ! min. Allo- the cr+cible coer and contents to cool and then determine their mass and record it in the data table. 2f the t-o mass meas+rements differ by no more than $.$" ( it can be ass+med that all of the -ater has been drien off. 5ther-ise repeat the process +ntil the mass no lon(er chan(es -hich indicated that all of the -ater has eaporated. Record this constant mass in the data table.


After recordin( the constant mass remoe the coer from the cr+cible and add a fe- drops of -ater -ith a beral pipet. Record obserations for this step.


Clean all apparat+s and the lab station. &ae s+re to completely sh+t off the (as ale before leain( the laboratory. Remember to -ash hands thoro+(hly. Place the rehydrated and anhydro+s chemicals in the disposal containers desi(nated by the teacher.

)esults*able 1+ ,ydrate -ata

&ass of empty cr+cible and coer1;.1" (2nitial mass of sample cr+cible and coer".11 (&ass of sample cr+cible and coer after first heatin("1.1< (&ass of sample cr+cible and coer after second heatin("1.$; (&ass of sample cr+cible and coer after third heatin( "1.$ (Constant mass of sample cr+cible and coer "1.$ (&ass of anhydro+s C+S5


)Constant mass = mass of empty cr+cible and coer > mass of anhydrate"1.$ ( = 1;.1" ( > ".<1 ( C+S5


&ass of -ater in the hydrate) 2nitial mass? constant mass > mass of -ater ori(inally in the compo+nd

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