4. Quality of observations/data 

 Consistent data 
Mass of water lost should be 4060% of the
mass of the hydrated salt. (Ideally, water is 51% of the
hydrated sample.) 
 Accurate measurements/observations 
Mass of salt after heating is less than before
heating. 
 Completed data table 
Data for all values determined experimentally
are recorded in the first four cells of data table. 
 Correct units 
All values for mass are in grams. 
 Qualitative description 
* 
5. Graph 
Not required for this task 
 Curve is appropriate to data trend 

 Points plotted accurately 

 Appropriate scale 

 Axes labelled with variables 

 Variables placed on correct axes 

6. Calculations 

 Calculated accurately 
All calculations are determined accurately
and consistent with significant figure rules. 
 Substituted correctly into relationship 
Converted numerical value for ratio to a whole
number ratio of moles X * moles H20. 
 Relationship stated or implied 
Determined numerical value by division for
mole ratio of anhydrous salt and water. 
 Units used correctly 
Used gram molecular weight of anhydrous salt
and GMW of water to correctly find moles of each. 
 Use of all data available 
Mass of anhydrous salt and mass of water are
calculated. 
7. Conclusion 

 Consistent with scientific principles 
Empirical formula represented in conclusion
is X * 7 H20. 
 Sources of error 
* 
 Consistent with data 
Moles of water in empirical formula were based
on experimental results. (1) 
 Relationship among variables stated 
Formula is represented as a whole number ratio
of moles of substance X to moles of H20 (X * H20). 
 Variables stated in conclusion 
Moles of X and moles of water are stated. 