Hope you'll have had a good weekend! Anyway, i am back to share with you more about my laboratory lesson in school today.
Today was about crystallization.
Introducing you to crystallization....
It is solution is the most common method used to purify soluble solids. There are many ways to carry out crystallization The seeding method allows you to grow a large single crystal, others allows you to grow many crystals at a time. By controlling the variables such as cooling rate and evaporation rate, the size and shape of the crystals can be controlled.
In order crystallization to take place, there are certain conditions that need to be met.Firstly, the solid in question must be soluble in water. Secondly, the solubility of the substance should change with change temperature. Thirdly, the solution used should be saturated with solution. Typically, the solution is heated to form a hot, saturation solution. The heating allows for excess solvent to be removed via evaporation. as the hot saturated solution cools. The dissolved solid appears as crystals as the solubility of the solute decreases with decreasing temperature. This means that as temperature of the solution drops less solute can be dissolved in the solution. The excess solution will then appear in the solution in the form of crystals.
After the entire experiment, i learned that crystals obtained by rapid cooling, meaning that the solution in the boiling tube is placed in a beaker of cold water. The crystals that are obtained are smaller and irregular. Crystals obtained by slow cooling, meaning it is heated slowly by hot water will result in becoming bigger and in a more regular shape.
This is how Copper (II) Sulphate looks like.
Some steps of the crystallization process.
Conclusion
Crystals formed by rapid cooling are smaller & less regular as compared to slow cooling.
Some questions to think about....
1. How can you obtain more crystals from the cooled copper (II) sulphate solution?
- Add more water to dissolve more copper sulphate.
- Add more copper sulphate
- Apply slow cooling instead of rapid cooling.
2. Suggest 2 reasons why in crystallization method we should stop heating before all the solvent evaporated.
- To prevent the copper sulphate from decomposing
- There will be soluble impurities will be left behind.
We also learned more about sublimation. In which, the solid turns from solid -> gas without passing through liquid. An example would be iodine (solid). When placed with sand and a funnel placed over it, it will emit "purple" coloured gas.
Sublimation set-up.
Result of sublimation of iodine solids.
After that, we continued doing our online activity called Are you good enough for it? Soon after that the class ended :) Thank you for reading!!
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