Fractional crystallization is a technique used for separating impurities from chemical products based on the differences in solubility with temperature. It involves dissolving impure solute in a hot solvent where the desired solute is less soluble than impurities. As the solution cools, the desired solute crystallizes out first, leaving impurities behind, resulting in the purification of the product. This method is particularly useful when dealing with substances that have different solubility behaviors with temperature.
What is fractional crystallization?
Fractional crystallization is a technique used for the separation of impurities from chemical products based on the different solubility behaviors of substances. It involves dissolving an impure solute in a hot solvent where the desired solute is less soluble than impurities. Upon cooling, the desired solute crystallizes out first, leaving impurities behind.
How does fractional crystallization work?
In fractional crystallization, the impure solute is dissolved in a hot solvent where the desired solute is less soluble than impurities. As the solution cools, the desired solute crystallizes out first due to its lower solubility, allowing for the separation of impurities from the pure product.
What is the purpose of fractional crystallization?
The main purpose of fractional crystallization is to purify a substance by separating it from impurities based on differences in solubility. This technique is commonly used in chemistry to obtain pure products from impure mixtures.
What are the key steps involved in fractional crystallization?
The key steps in fractional crystallization include dissolving the impure solute in a hot solvent, allowing the solution to cool slowly, and isolating the pure crystals of the desired solute as they separate out from the solution. This process is repeated to enhance the purity of the final product.
How does the solubility behavior of substances impact fractional crystallization?
Substances with different solubility behaviors exhibit varying rates of crystallization during fractional crystallization. Compounds with rapid changes in solubility with temperature, like KNO3, are suitable for fractional crystallization as they can be easily separated from impurities based on their solubility differences.
What is the main purpose of fractional crystallization in separating impurities from chemical products?
a) Rapid dissolution of impurities
b) Selective separation of desired solute
c) Uniform cooling of the solution
d) Instant crystallization of all components
Answer: b) Selective separation of desired solute
Which of the following substances shows a rapid change in solubility with temperature, making it suitable for fractional crystallization?
a) KBr
b) Na2SO4.10H2O
c) KCl
d) Alanine
Answer: b) Na2SO4.10H2O
What happens at the break in a discontinuous solubility curve during fractional crystallization?
a) New solid phase disappears
b) Solute concentration remains constant
c) New solid phase appears
d) Impurities dissolve completely
Answer: c) New solid phase appears
In fractional crystallization, what is the basis for separating impurities from the chemical products?
a) Rapid dissolution of all components
b) Gradual change in solubility with temperature
c) Selective crystallization of desired solute
d) Instant separation of impurities
Answer: c) Selective crystallization of desired solute
Which technique involves dissolving impure solute in a hot solvent to separate out the desired solute first during cooling?
a) Fractional Distillation
b) Fractional Crystallization
c) Rapid Dissolution
d) Selective Precipitation
Answer: b) Fractional Crystallization