Assertion & Reason Test: The s-Block Elements


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QUESTION: 1

In the following questions more than one option of column I and II may be correlated. Match the elements given in Column I with the properties mentioned in Column II.

Solution:

(i) Li - Due to very high hydration enthalpy, E0 is most negative.

(ii) Na - Na gives NaOH (strong base). One mole of it replaces 1 mol H+ from acid therefore it is the strongest monoacidic base.

(iii) Ca - Hydration energy is very low therefore, calcium oxalate is insoluble.

(iv) Ba - Hydration energy is low as the size Ba2+ is large therefore barium sulphate is insoluble. 6s2 is valence shell electronic configuration.

QUESTION: 2

In the following questions more than one option of column I and II may be correlated. Match the elements given in Column I with the properties mentioned in Column II.

Match the compounds given in Column I with their uses mentioned in Column II.

Solution:

(i) CaCO3 - Specially precipitated CaCO3 ​is used in the manufacture of high quality paper.

(ii) Ca(OH)2 - It is used in white wash due to its disinfectant nature and sparingly soluble in water.

(iii) CaO - It is used in the manufacture of Na2CO3 ​ from NaOH.

(iv) CaSO4 - It is used in dentistry and ornamental work.

QUESTION: 3

In the following questions more than one option of column I and II may be correlated. Match the elements given in Column I with the properties mentioned in Column II.

Match the elements given in Column I with the colour they impart to the flame given in Column II.

Solution:

Here tow tables are provided. In column 1 number of metals are given and in column 2 their colour in flame test is given. Cs shows blue colour in flame test. Na shows yellow colour in flame test. K shows violet colour in flame test. Ca shows brick red colour in flame test. Sr shows crimson red colour in flame test. Ba shows apple green colour in flame test.

QUESTION: 4

In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): The carbonate of lithium decomposes easily on heating to form lithium oxide and CO2.

Reason (R): Lithium being very small in size polarises large carbonate ion leading to the formation of more stable Li2O and CO2.

Solution: Unlike other alkali metal carbonates which are stable in heat Lithium being very small in size polarises a large CO32– ion leading to the formation of more stable Li2O and CO2.

Li2CO3 → Li2O + CO2

Polarisation is the distortion of electron cloud of the anion CO32- by the cation Li2+.

QUESTION: 5

In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A) : Beryllium carbonate is kept in the atmosphere of carbon dioxide.

Reason (R) : Beryllium carbonate is unstable and decomposes to give beryllium oxide and carbon dioxide.

Solution: Beryllium carbonate is kept in the atmosphere of carbon dioxide as it is unstable and decomposes to give beryllium oxide and carbon dioxide.

BeCO3 ​⇌ BeO + CO2

When they are stored in the atmosphere of CO2, the concentration of CO2 increases in the right side, making the reaction to shift towards backside so that the decomposition of beryllium carbonate is prevented.

QUESTION: 6

Choose the correct statements from the following.

(i) Beryllium is not readily attacked by acids because of the presence of an oxide film on the surface of the metal.

(ii) Beryllium sulphate is readily soluble in water as the greater hydration enthalpy of Be2+ overcomes the lattice enthalpy factor.

(iii) Beryllium exhibits coordination number more than four.

(iii) Beryllium oxide is purely acidic in nature.

Solution:
  • Beryllium does not exhibit coordination number more than four as in its valence shell there are only four orbitals.

  • Beryllium oxide is amphoteric in nature.

QUESTION: 7

Which of the following are the correct reasons for anomalous behaviour of lithium?

(i) Exceptionally small size of its atom

(ii) Its high polarising power

(iii) It has high degree of hydration

(iv) Exceptionally low ionisation enthalpy

Solution: Lithium has high ionization enthalpy and also the high degree of hydration.This is due to its small size.
QUESTION: 8

When Zeolite, which is hydrated sodium aluminium silicate is treated with hard water, the sodium ions are exchanged with which of the following ion(s)?

(i) H+ ions

(ii) Mg2+ ions

(iii) Ca2+ ions

(iv) SO42– ions

Solution: Permutit or zeolites are packed in a suitable container and a slow stream of hard water is passed through this material. As a result, calcium and magnesium ions present in hard water are exchanged with sodium ions in the permutit (Na + Al-Silicate). The outgoing water contains sodium salts, which do not cause hardness.

CaCl2 ​+ 2Na+ → Ca(Al−silicate)2 ​+ 2NaCl

MgCl2 ​ + 2Na+ → Ca(Al−silicate)2 ​+ 2MgCl

So here the sodium ions are exchanged with both Ca2+ and Mg2+ ions.

QUESTION: 9

Amphoteric hydroxides react with both alkalies and acids. Which of the following Group 2 metal hydroxides is soluble in sodium hydroxide?

Solution: On reaction with NaOH, Be(OH)2 forms beryllate ion, becoming soluble in it. Be(OH)2 + 2OH- → [Be(OH)4]2
QUESTION: 10

A chemical A is used for the preparation of washing soda to recover ammonia. When CO2 is bubbled through an aqueous solution of A, the solution turns milky. It is used in white washing due to disinfectant nature. What is the chemical formula of A?

Solution:

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