4 Marks Questions

Question 14 Marks

The mole fraction of helium in a saturated solution at $20^\circ C$ is $1.2 g 10-6.$ Find the pressure of helium above the solution. Given Henry's constant at $20^\circ C$ is $144.97\ k\ bar. (2)$

Answer

$ p _{ He }= K _{ Hx } \times X _{ He }$
$=\left(144.97 \times 10^3 \text { bar }\right)\left(1.2 \times 10^{-6}\right)$
$=0.174 \text { bar }$

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Question 24 Marks

Read the following text carefully and answer the questions that follow:
Aariv Sharma is very fond of a special drink made by his grandmother using different fruits available in their hometown. It has an outstanding taste and also provide great health benefits of natural fruits. He thought of utilizing his grandmother recipe to create a new product in the beverage market that provide health benefits and also contain fizziness of various soft drinks available in the market.
$i.$ How he can add fizz to the special drink made by his grandmother?
$ii.$ What is the law stated in the chapter that can help Aariv to make his drink fizzy?
$iii.$ What precautions he should take while bottling so that his product does not lose fizz during storage and handling across long distances?

Answer

$i.$ Carbondioxide is a gas which provide fizz and tangy flavour. He can dissolve Carbondioxide gas in the drink.
$ii.$ Henry's law which states that solubility of a gas in liquid is directly proportional to partial pressure of the gas.
$iii.$ Bottles should be sealed under high pressure of $CO_2$ and capping should be done perfectly to avoid leakage of $CO_2$ as any loss of partial pressure will result into decrease in solubility.

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Question 34 Marks

Crystal structure of oxides of transition metals often show defects. Given reason. (2)

Answer

The actual oxide structures, generally show departures from a regular arrays due in part to distortions caused by packing of ions of different size and to ligand field effects.

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Question 44 Marks

Read the following text carefully and answer the questions that follow:
The transition metals when exposed to oxygen at low and intermediate temperatures form thin, protective oxide films of up to some thousands of Angstroms in thickness. Transition metal oxides lie between the extremes of ionic and covalent binary compounds formed by elements from the left or right side of the periodic table. They range from metallic to semiconducting and deviate by both large and small degrees from stoichiometry. Since delectron bonding levels are involved, the cations-exist in various valence states and hence give rise to a large number of oxides. The crystal structures are often classified by considering a cubic or hexagonal close-packed lattice of one set of ions with the other set of ions filling the octahedral or tetrahedral interstices. The actual oxide structures, however, generally show departures from such regular arrays due in part to distortions caused by packing of ions of different size and to ligand field effects. These distortions depend not only on the number of d-electrons but also on the valence and the position of the transition metal in a period or group.
i. Why does copper, which is in first series of transition metal exhibits +1 oxidation state most frequently? (1)
ii. The lowest oxide of transition metal is basic. Why? (1)
iii. The variability in oxidation states of d-block different from that of the p-block elements. Explain. (2)

Answer

i. Copper readily loses one electron from its 4s orbital, to form stable 3d electronic configuration.
ii. The lower oxide of transition metal has low oxidation states. This means some of the valence electrons of the metal atoms do not participate in bonding. Thus, they can donate electrons and can behave as bases.
iii. In p-block, lower oxidation state is more stable due to inert pair effect, whereas in d-block elements higher oxidation states states are more stable. In d-block, oxidation states differ by one, whereas in p-block, it differs by two.

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Chemistry 4 Marks Questions

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