Hydrated Crystals Lab Conclusion Essay
Determined mass of anhydrous salt by subtracting the mass of the crucible and lid, from the mass of the crucible, lid, and anhydrous salt: 1.1434g
Determined mass of the water lost by subtracting the mass of the anhydrous salt, from the hydrous salt: 1.018g
Calculated the percentage of water in the hydrated salt:
Determined amount of anhydrous salt by dividing the mass of the copper sulfide by the number of grams per mole, in 1 mole of copper sulfide: 0.01058mol
Determined amount of water lost, by dividing the mass of the water lost during heating, by the number of grams per mole in 1 mole of water: 0.0565mol
Calculated the molar ratio:
Rounded to the nearest integer, the ratio is 1:5.
This means that the formula for hydrated copper sulfate is:
The goal of this experiment is to determine the percentage of water (by mass) in a hydrate, and to calculate the ratio of salt to water in a hydrated salt. To achieve this, a known mass of hydrated salt was heated, evaporating the water (essentially distillation). Given that the mass of the hydrated salt is known, it is also given that the mass lost is equivalent to the mass of the water. By comparing the mass lost to the mass of anhydrous salt left behind, we can calculate the percentage of water within the hydrated salt. We can also (via stochiometric and molar ratios), calculate the ratio of salt to water.
Given the data presented above, findings showed the experimental percentage of water within the hydrated salt to be: 47.10%
The accepted percentage of water within hydrated copper sulfate is: 36.07%
As such, the percent error within this measurement is 30.57%
The experimental stoichiometric ratio between copper sulfate and water was found to be: 1:5.314
The accepted stoichiometric ratio between copper sulfate and water is: 1:5
The percent error within this measurement is 5.909%
The formula for hydrated copper sulfate is:
Possible reasons for such error:
- The anhydrous salt could have been exposed to air prior to measurement, and reabsorbed some moisture, thus disrupting measurements. (Unlikely, considering that the ratios between the two, both stoichiometric and percent water content, would be smaller in such an instance.)
- Not all of the water may have evaporated during heating (Also unlikely, for the same reason as the one above.)
- During heating, some of the hydrous salt may have spattered, thus removing a portion of the hydrous salt from the crucible (A more likely source of error, considering that this would result in a greater difference between the two ratios, and percentages.)
- Human error is always in effect, given that the laboratory does not function under ideal conditions. As such, there is always the possibility of inaccuracies with measurement, perception of measurement, inaccuracies of equipment, and other such errors. (However, this is not likely to be the sole cause of the inaccuracies within this experiment, though it may contribute to it.)
Possible improvements that could be made to this experiment in the future could include increasing the sample size, to produce a more average measurement. Another possibility would be to get more accurate equipment, to replicate the experiment within a dehumidified environment, and/or perform the experiment using a larger crucible (to reduce the possibility that spatter from the hydrated salt could leave the crucible).
,rea +p any lar(e crystals before placin( them in the cr+cible. *etermine the mass of the coered cr+cible and crystals to the nearest $.$1 ( and record the mass in the data table.
Place the cr+cible -ith the copper s+lfate hydrate on the trian(le and a(ain position the coer so there is only a small openin(. 2f the openin( is too lar(e thecrystals may spatter as they are heated. Heat the cr+cible ery (ently on a lo- flame to aoid spatterin(. 2ncrease the temperat+re (rad+ally for " or min. and then heat +ntil the cr+cible (lo-s red for at least ! min. ,e ery caref+l not to raise the temperat+re of the cr+cible and its contents too s+ddenly. A color chan(e -ill occ+r -hich is normal b+t if the s+bstance remains yello- after coolin( it -as oerheated and has be(+n to decompose. Remoe the cr+cible from the flame and allo- it and its contents 3
!ake sure the crucible is covered$
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 coer positioned as in step ! and contents to redness a(ain for ! min. Allo- the cr+cible coer 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 drien off. 5ther-ise repeat the process +ntil the mass no lon(er chan(es -hich indicated that all of the -ater has eaporated. Record this constant mass in the data table.
After recordin( the constant mass remoe the coer from the cr+cible and add a fe- drops of -ater -ith a beral pipet. Record obserations for this step.
Clean all apparat+s and the lab station. &ae s+re to completely sh+t off the (as ale before leain( 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 coer1;.1" (2nitial mass of sample cr+cible and coer".11 (&ass of sample cr+cible and coer after first heatin("1.1< (&ass of sample cr+cible and coer after second heatin("1.$; (&ass of sample cr+cible and coer after third heatin( "1.$ (Constant mass of sample cr+cible and coer "1.$ (&ass of anhydro+s C+S5
)Constant mass = mass of empty cr+cible and coer > 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