# Effect of Time on Rate of Crystallization

Aim: To study the effect of time on the rate of crystallization

Requirements:

Chemicals: Potassium nitrate, Water.

Apparatus/ Instrument: Thermometer, Water Bath, Tripod Stand, Test tube, Stop Clock.

Principle:

• Crystallization is the process of forming a crystalline material from a liquid, gas, or amorphous solid. The crystals thus formed have highly regular internal structures, the basis of which is called the crystal lattice.
• All crystallization processes are aimed at creating a supersaturated solution or melt. Supersaturation is the driving force under whose influence new crystals are formed and present crystals grow.
• For most substances, the solubility increases with increasing temperature.

Procedure:

Effect of time on the rate of Crystallization

1. 75 gm of potassium nitrate is accurately weighed (W1 g).
2. 100ml of water is transferred into a 250ml beaker.
3. The beaker containing water is placed in a constant temperature water bath maintained at 50 0C.
4. Potassium nitrate is added into the water little by little, the solution is stirred with a glass rod to dissolve the solute.
5. The process is continued until a saturated (with a little excess of solutes) solution is formed.
6. The weight of potassium nitrate remained as weighed (W2 g). The difference in the weight W= (W1-W2 gm) gives the weight of potassium nitrate added into 100ml water.
7. From this 10ml of the saturated solution is transferred into 9 beakers.
8. All beakers are placed into an ice bath at once. The temperature of the solution decreases suddenly due to shock cooling forming a supersaturated solution. Nucleation and crystal growth take place.
9. Ager 10 minutes the solution of the first beaker is filtered to collect the crystals.
10. This is repeated ager 10 minutes there ager using the solutions of the remaining beakers.
11. All the crystals are collected on the filter paper separately and are subjected to drying using the dryer.
12. The weight of each sample of crystals is recorded.
13. A graph is plotted taking time on X – the axis and percentage (%) weight of crystal on the y-axis.

Observation Table:

A = weight of potassium nitrate present in 10 ml of water (Theoretical weight)

RESULT:

The effect of time on the rate of crystallization is‐‐‐‐‐‐‐

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