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Chemistry Case study (4 Marks)

Model Paper 1 · Rajasthan Board (RBSE) STD 11 Science (Rajasthan - English Medium). 2 questions.

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Case study (4 Marks)

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Question 14 Marks
Chromatography is an important technique extensively used to separate mixtures into their components, purify compounds and also test the purity of compounds. Based on the principle involved, chromatography is classified into different categories. Two of these are Adsorption chromatography and Partition chromatography. Two main types of chromatographic techniques are based on the principle of differential adsorption column chromatography, and thin-layer chromatography. Adsorption chromatography is based on the fact that different compounds are adsorbed on an adsorbent to different degrees. Column chromatography involves the separation of a mixture over a column of adsorbent (stationary phase) packed in a glass tube. Thin-layer chromatography (TLC) is another type of adsorption chromatography, which involves the separation of substances of a mixture over a thin layer of an adsorbent coated on a glass plate. Partition chromatography is based on the continuous differential partitioning of components of a mixture between stationary and mobile phases.

1. Which adsorbent is used in adsorption chromatography?
2. How do you visualize colourless compounds after separation in Paper Chromatography?
3. Why paper chromatography is a type of partition chromatography?
OR
Which chromatography is shown in following image?
Image
Answer
1. In column chromatography adsorbent is silica gel or alumina while in paper chromatography adsorbent is cellulose.
2. In paper chromatography the spots of the separated colourless components may be observed either under ultra-violet light or by the use of an appropriate spraying agent.
3. Partition chromatography is based on continuous differential partitioning of components of a mixture between stationary and mobile phases as doner in paper chromatography.
OR
Column chromatography.
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Question 24 Marks
In order to explain the characteristic geometrical shapes of polyatomic molecules, Pauling introduced the concept of hybridisation. The orbitals undergoing hybridisation should have nearly the same energy. There are various type of hybridisations involving s, p and d-type of orbitals. The type of hybridisation gives the characteristic shape of the molecule or ion.

1. Why all the orbitals in a set of hybridised orbitals have the same shape and energy?
2. Out of $XeF _2$ and $SF _2$ which molecule has the same shape as $NO _2^{+}$ion?
3. Out of $XeF _4$ and $XeF _2$ which molecule doesn't have the same type of hybridisation as P (Phosphorus) has in $PF _5$ ?
OR
Unsaturated compounds undergo additional reactions. Why?
Answer
1. Hybrid orbitals are formed after combining atomic orbitals and have the equivalent shape and energy in the given set of hybridised orbitals.
2. $XeF _2$ molecule has the same shape as $NO _2^{+}$ion.
3. $XeF _4$ molecule doesn't have the same type of hybridisation as P (Phosphorus) has in $PF _5$.
OR
Unsaturated hydrocarbon molecules include two- or three-fold bonds of carbon. The $\pi$-bond is a multiple bond, which becomes unstable and hence adds across numerous bonds.
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Case study (4 Marks) - Chemistry STD 11 Science Questions - Vidyadip