Waters of crystallization grade 10

Notes on waters of crystallization for Physical Sciences

1. QUANTITATIVE ASPECTS OF CHEMICAL CHANGE: WATERS OF CRYSTALLIZATION COMPILED BY Ms. LQ RAMOTSABI

2. Waters of crystallization Definition The water molecules attached to an ionic crystal compound. The ionic compound is called a hydrate because it contains water in it

3. The hydrate salt has the following chemical formula e.g. The is the ionic crystal compound The 10 represents the number of moles of water molecules that are in the compound.  

4. How to find the amount of waters of crystallization in a compound?.. We can find the amount of waters of crystallization by heating the crystal The waters of crystallization will evaporate and the crystal remains. The reaction has the following equation: By weighing the starting and end products, we can determine the amount of water that was in the hydrate salt

5. Continued A typical calculation problem will require you to find the number of moles of the water molecules in the compound (the value of x)

6. LET’S DO AN EXAMPLE Aluminium trichloride ( ) is an ionic substance that forms crystals in the solid phase. Water molecules may be trapped inside the crystal lattice. We represent this as: ⋅x .Carine heated some aluminium trichloride crystals until all the water had evaporated and found that the mass after heating was 2,8 g. The mass before heating was 5,08 g. What is the number of moles of water molecules in the aluminium trichloride before heating ?  

7. Find the number of water molecules We first need to find n, the number of water molecules that are present in the crystal. To do this we first note that the mass of water lost is 5,08 g−2,8 g=2,28 g. Find the mass ratio The mass ratio is: : 2,8 : 2,28 Find the mole ratio  

8. To work out the mole ratio we divide the mass ratio by the molecular mass of each species: Next we convert the ratio to whole numbers by dividing both sides by the smaller amount: : : : 1 : 6   Formula to find number of moles: n= n n 0,02099 0,1266 n n 0,02099 0,1266

9. continued The mole ratio of aluminium trichloride to water is 1:6 And now we know that there are 6 moles of water molecules in the crystal. The formula is Also look at the example we did that is on the resource pack. It is also about waters of crystallization but not number of moles, rather its percent composition.  

10. The end