Chemistry Class 11 NCERT Solutions: Chapter 10 the s Block Elements Part 8

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Q: 24. Explain the significance of sodium, potassium, magnesium, and calcium in biological fluids

Answer:

Importance of sodium, potassium, magnesium, and calcium in biological fluids:

(i) Sodium (Na):

Sodium ions are found primarily in the blood plasma. They are also found in the interstitial fluids surrounding the cells.

(A) Sodium ions help in the transmission of nerve signals

(B) They help in regulating the flow of water across the cell membranes

(C) They also help in transporting sugars and amino acids into the cells

(ii) Potassium (K):

Potassium ions are found in the highest quantity within the cell fluids

(A) K ions help in activating many enzymes.

(B) They also participate in oxidising glucose to produce ATP

(C) They also help in transmitting nerve signals.

(iii) Magnesium (Mg) and calcium (Ca):

Magnesium and calcium are referred to as macro-minerals. This term indicates their higher abundance in the human body system.

(A) helps in relaxing nerves and muscles

(B) helps in building and strengthening bones

(C) maintains normal blood circulation in the human body system

(D) helps in the coagulation of blood

(E) also helps in maintaining homeostasis

Q: 25. What happens when

(i) Sodium metal is dropped in water?

(ii) Sodium metal is heated in free supply of air?

(iii) sodium peroxide dissolves in water?

Answer:

(i) When metal is dropped in water, it reacts violently to form sodium hydroxide and hydrogen gas. The chemical equation involved in the reaction is:

(ii) On being heated in air, sodium reacts vigorously with oxygen to form sodium peroxide. The chemical equation involved in the reaction is:

(iii) When sodium peroxide is dissolved in water, it is readily hydrolysed to form sodium hydroxide and water. The chemical equation involved in the reaction is:

Q: 26. Comment on each of the following observations:

(A) The mobilities of the alkali metal ions in aqueous solution are

(B) Lithium is the only alkali metal to form a nitride directly.

(C) is nearly constant.

Answer:

(A) On moving down the alkali group , the ionic and atomic sizes of the metals increase. The given alkali metal ions can be arranged in the increasing order of their ionic sizes as:

Smaller the size of an ion, the more highly is it hydrated. Since is the smallest, it gets heavily hydrated in an aqueous solution. On the other hand, is the largest and so it is the least hydrated. The given alkali metal ions can be arranged in the decreasing order of their hydrations as:

Greater the mass of a hydrated ion, the lower is its ionic mobility. Therefore, hydrated is the least mobile and hydrated is the most mobile. Thus, the given alkali metal ions can be arranged in the increasing order of their mobilities as:

(B) Unlike the other elements of group 1, reacts directly with nitrogen to form lithium nitride. This is because is very small in size and so its size is the most compatible with the ion. Hence, the lattice energy released is very high. This energy also overcomes the high amount of energy required for the formation of the ion.

(C)Electrode potential (E°) of any electrode depends upon three factors:

(i) Ionisation enthalpy

(ii) Enthalpy of hydration

(iii) Enthalpy of vaporization

The combined effect of these factors is approximately the same for Hance, their electrode potentials are nearly constant.