Important Questions Class 12 Chemistry Chapter 7

Important Questions Class 12 Chemistry Chapter 7

Important Questions For CBSE Class 12 Chemistry Chapter 7 – The P-Block Elements

The Modern Periodic Table is crucial for gaining knowledge about the properties of elements arranged based on their atomic numbers. The elements placed in the Groups 13 to 18 of the Periodic Table are called p-block elements as the last electron enters the outermost p-subshell of the atom. Except for helium, all the p-block elements share the same electronic configuration (ns2np1-6). Students must learn all the concepts very well if they want to understand the physical and chemical properties of the p-Block elements.

Important Questions Class 12 Chemistry Chapter 7 will help students revise the chapter and practise questions that are important for the board exam. This set of questions has been prepared by Extramarks by subject matter experts after analysing the questions from the past years. The updated CBSE Syllabus has been followed before selecting the questions. Therefore, students can practise the Chapter 7 Class 12 Chemistry Important Questions to score more in the exam.

CBSE Class 12 Chemistry Chapter-7 Important Questions

Study Important Questions for Class 12 Chemistry Chapter 7 – The p-Block Elements

Given below is a sample of Class 12 Chemistry Chapter 7 Important Questions. For the full set of questions, students can access the link on the Extramarks website.

Very Short Answer Type Questions
1 Marks

Q.1. The maximum covalency of the nitrogen atom is 4, but the heavier elements of group 15 show a covalency greater than that of nitrogen. State the reason.

Ans. The heavier elements of Group 15 have vacant d-orbitals whereas in a nitrogen atom there is no d-orbital, in its valence shell. Only four electrons can be accommodated in its valence shells because of the presence of one 2s and three 2p orbitals. Hence, the covalency of nitrogen cannot be more than 4.

Q.2. Why is bismuth (Bi) a stronger oxidant than antimony (Sb)?

Ans. Bismuth can gain electrons from reducing agents faster than antimony and becomes stable quickly. So, bismuth is a stronger oxidant than antimony.

Q.3.Why does the tendency of elements in Group 15 to exhibit -3 oxidation state decrease as we move down in the Periodic Table?

Ans. The tendency of exhibiting -3 oxidation states decreases in group 15 elements as we move down in the Periodic Table due to the increase of the size of atoms and metallic character and decrease in electronegativity.

Q.4. Why is the boiling point of PH3 less than the boiling point of NH3?

Ans. The strong hydrogen bond in NH3 molecules causes a higher boiling point; whereas such a strong intermolecular hydrogen bond cannot be formed in PH3 molecules because of the lesser electronegativity in the large molecules of the compound.

Q.5. The bond dissociation energy of F2 is less than that of Cl2. Explain the reason.

Ans. The atomic size of F2 is smaller than that of Cl2, which causes a greater repulsive force between the lone pair electrons present in the F2 atom. So, the required bond dissociation energy of F2 is less than that of Cl2.

Short Answer Type Questions
2 Marks

Q.1. Which one of the two is chemically more active, red phosphorus or white phosphorus? Why?

Ans. The atoms of white phosphorus have a tetrahedral structure where the angle is 60⁰. Such atomic structure causes more angular strain in white phosphorus atoms, which makes them unstable. However, red phosphorus is a polymer of P4 that has a lesser angular strain, making it more stable. The elements that are more unstable tend to react with other elements. Therefore, white phosphorus is more reactive than red phosphorus.

Q.2. What are the conditions required for preparing ammonia by Haber’s Process?

Ans. To prepare ammonia by Haber’s Process, the following requirements must be met.

• The reaction should take place under high pressure (200 atm).
• Moderate temperature is needed (700 K).
• Fe or FeO is required to act as a catalyst.
• Along with the catalyst, a small amount of K2O and Al2O3 help increase the rate of reaction.

Q.3. (i) Write one important use of ClF3 .

(ii) Write down the composition of bleaching powder.

Ans. (i) ClF3 is widely used in the semiconductor industry, to clean the surfaces of chemical vapour disposition chambers.

(ii) The composition of bleaching powder is as follows: Ca(OCl)2.CaCl2.Ca(OH)2.2H2O.

Q.4. What are the important uses of chlorine dioxide hydrate?

Ans. a. Chlorine dioxide hydrate or ClO2 is used for purifying drinking water.

1. It is also used for bleaching wood pulp, cellulose, refined flour for making white breads, etc.
2. The diluted ClO2 is also used as mouth freshener.

Long Answer Type Questions
5 Marks

Q.1. Why is H2S more acidic than H2O? What is the reason that H3PO2 acts as a good reducing agent while H3PO4 does not? Which inert gas is used in balloons?

Ans. The S−H bond in H2S is weaker than the O−H bond of H2O. Besides, the electronegativity of oxygen is higher than Sulphur. Therefore, the bond dissociation enthalpy is lower in case of H2S. So, it can be dissociated easily. Hence, H2S is more acidic than H2O.

The element or compound having lower oxidation state does not tend to act as a reducing agent. The oxidation state of H3PO4 is lower than that of H3PO2 due to the absence of the P−H bond in H3PO4 molecule. Hence, H3PO4 does not act as a reducing agent.

Helium is the inert gas that is used to blow up a balloon.

Q.2. What are the by-products of the reaction between copper (Cu) and concentrated nitric acid (HNO3)? Write the chemical equation for the reaction between CuSO4 and PH3. When does sulphur act as a paramagnetic element?

Ans. If Cu and concentrated HNO3 react with each other, they produce copper nitrate (Cu(NO3)2), nitrogen dioxide (NO2), and water as by-products.

The chemical equation for the reaction is as follows: 3CuSO4 + 2PH3 → Cu3P2 + 3H2SO4.

In the vapour state, sulphur exists as S2 with two unpaired electrons in the antibonding * orbital. Therefore, in its vapour state, sulphur acts as a paramagnetic element.

Q.3. Write some of the applications of argon and neon in daily life.

Ans. (i) Uses of argon:

1. As argon is an inert gas, it is used to create a non-reactive environment at the high temperatures required for welding alloys and different metals.
2. The gas that is present in electric bulbs is argon.
3. Argon is also used in radio valves.

(ii) Uses of neon:

1. Neon gas is used in fluorescent lamps and on boards displaying advertisements.
2. It is one of the most widely used gases in botanical gardens.
3. In voltage regulators and indicators, neon gas is also used.

Q.4.  How does sulphur dioxide affect architecture and living organisms?

Ans. (i) The effect of sulphur dioxide on architecture: Sulphur dioxide reacts with moisture present in the atmosphere and produces sulphurous acid (H2SO3) that destroys construction materials, such as marbles.

(ii) The effect of sulphur dioxide on living organisms:

1. Sulphur dioxide causes the common plant disease chlorosis. It can also slow down the process of chlorophyll synthesis which eventually leads to the death of plant cells.
2. This gas also causes respiratory diseases, coughing and the redness of eyes.

Class 12 Chemistry P Block Elements Important Questions And Solutions: Summary

Chemistry Class 12 Chapter 7 Important Questions aims to help students recapitulate the entire chapter. Students can focus on practising questions and develop their time management skills. The p-block elements constitute an important part of chemistry, and many conceptual questions can be asked from this chapter. Therefore, students must not neglect this chapter and prepare well for the exam. The topics discussed so far in the question-answer format are given in brief below.

The p-block elements occupy the Groups from 13 to 18. All of them have a similar electronic configuration (ns2np1-6). The outermost shell is crucial for determining the covalency of the elements. The nitrogen atom can place only four electrons in its outermost shell. So, its covalency cannot be more than 4 though p-block elements (group 15) show a covalency greater than that of nitrogen.

The Important Questions include Haber’s Process for producing ammonia, effects of pollutants like sulphur, the disinfecting and bleaching properties of chlorine, hydrides, dissociation enthalpy, etc. that students must have in-depth knowledge about to obtain excellent marks in the exams. Students will also learn about some important chemical reactions, their importance, and how to present them through equations.

The questions also cover topics like why some elements are chemically more active than others, in which conditions sulphur shows paramagnetism, the properties of reducing agent and oxidising agents, etc. It is noteworthy that though some elements are chemically inactive, they are still useful in daily life. For example, helium, neon, and argon. The cylinder that scuba divers use for diving in the deep sea contains helium gas. The cylinder that contains air also contains nitrogen gas in it which is highly soluble in blood and may cause death of the divers. Helium gas is used to reduce the effect of nitrogen. Students can refer to the questions for further clarification.

Why Should You Study P-Block Elements?

There are numerous elements on the earth. It is not possible to remember the characteristics of each of them individually. Therefore, the Periodic Table was invented to make the study of elements convenient. One can easily tell the properties, electronic configuration and other necessary details by knowing the position of the given element in the periodic table. There are many p-block elements, but we study them as a separate group because they share similar features.

Oxygen, the gas most important for the existence of life, is a p-block element (Group 16). Carbon which is required by plants during photosynthesis is also a p-block element (Group 14). Similarly, other important gases like nitrogen (Group 15), noble gases (Group 18) also belong to the group of p-block elements. As a result, students must have in-depth knowledge about these elements. This makes the study of p-block elements crucial. Besides, this chapter is also important from the perspective of the exam. Students must prepare the chapter very well to obtain better marks in the exam.