NCERT Solutions for Class 11 Chemistry Chapter 10 The s-Block Elements- In this chapter, we will study the s-block elements of the periodic table. The s-block elements of the periodic table are those elements in which the last electron enters the outermost s-subshell (or s-orbital). Two electrons are the maximum capacity of ns energy subshell. In this chapter, there are 32 questions in the exercise. The NCERT Solutions for Class 11 Chemistry Chapter 10 The s-Block Elements are designed and solved by our chemistry experts. These are the detailed explanation of NCERT textbook questions. These solutions of NCERT for class 11 chemistry chapter 10 The s-Block Elements help students in their preparation of class 11 final examination as well as in the various competitive exams like JEE, NEET, BITSAT etc.
In s-block, there is a total of two groups (1&2). In NCERT solutions for Class 11 Chemistry Chapter 10 The s-Block Elements we will discuss important concepts of s-block elements like properties of group 1 and group 2 elements, their electronic configuration, their occurrence, general characteristics of the compounds of alkali metals and alkaline earth metal, anomalous behaviour of lithium and beryllium, important compounds of sodium and calcium and at the end we will discuss the biological importance of sodium, potassium, magnesium and calcium.
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We already discussed that s-block elements are divided into two groups. The elements of Group 1 are lithium(Li), sodium(Na), potassium(K), rubidium(Rb), caesium(Cs) and francium(Fr). They are collectively known as the alkali metals. The elements of Group 2 beryllium(Be), Magnesium(Mg), Calcium(Ca), Strontium(Sr), Barium(Ba) and Radium(Ra). They are collectively known as alkaline earth metals. In NCERT solutions for Class 11 Chemistry Chapter 10 The s-Block Elements, we will also discuss some important trends like atomic radius, diagonal relationship etc.
Some Important points of Class 11 Chemistry Chapter 10 The s-Block Elements
1. General electronic configuration of Group 1 elements is .
2. General electronic configuration of Group 2 elements is .
3. Generally, densities of alkali metals increase down the group from Li to Cs except for density of K < Na.
4. Alkali metals have low boiling and melting point and these decreases down the group.
Topics of NCERT Grade 11 Chemistry Chapter 10 The s-Block Elements
10.1 Group 1 Elements: Alkali Metals
10.2 General Characteristics of the Compounds of the Alkali Metals
10.3 Anomalous Properties of Lithium
10.4 Some Important Compounds of Sodium
10.5 Biological Importance of Sodium and Potassium
10.6 Group 2 Elements: Alkaline Earth Metals
10.7 General Characteristics of Compounds of the Alkaline Earth Metals
10.8 Anomalous Behaviour of Beryllium
10.9 Some Important Compounds of Calcium
10.10 Biological Importance of Magnesium and Calcium
NCERT Solutions for Class 11 Chemistry Chapter 10 The s-Block Elements - Exercise Questions
Physical and chemical features of alkali metals-
All the alkali metals are silvery white, soft and light metals. Because of the large size, these elements have a low density which increases down the group from Li to Cs. However, potassium is lighter than sodium.
The melting and boiling points of the alkali metals are low indicating weak metallic bonding due to the presence of only a single valence electron in them.
The alkali metals and their salts impart characteristic colour to an oxidizing flame.
Due to low ionisation enthalpy, they are highly reactive. As we move down the group reactive nature increases.
The alkali metals tarnish in dry air due to the formation of their oxides which in turn react with moisture to form hydroxides. They burn vigorously in oxygen forming oxides. Lithium forms monoxide, sodium forms peroxide, the other metals form superoxides. The superoxide ion is stable only in the presence of large cations such as K, Rb, Cs.
The alkali metals react with water to form hydroxide and dihydrogen.
Question 10.2 Discuss the general characteristics and gradation in properties of alkaline earth metals
The general characteristics and gradation in properties of alkaline earth metals-
General electronic configuration is [noble gas].
Have two electrons to lose and attain their nearest noble gas configuration.
have smaller atomic and ionic radii than corresponding alkali metals in the same periods.
First IE is higher than those elements of group 1
electropositive nature increase down the group from Be to Ba.
they give a positive flame test by imparting different colours.(except Be and Mg)
Be and Mg are inert to oxygen and water. this is because of the formation of a thin layer of oxide on their surface.(powdered Be give BeO and .
React with halogens at high temperature to form halogen halides. here M = alkaline metals and X = halogen elements
All alkaline metals react with hydrogen and form hydrides except for Beryllium
React with acids to form salts and produce dihydrogen gas.
Act as a reducing agent but not as powerful as alkali metals. Down the group reducing power decreases.
Also, dissolve in liquid ammonia and give the deep blue coloured solution.
Question 10.3 Why are alkali metals not found in nature ?
Electronic Configuration All the alkali metals have one valence electron, outside the noble gas core. The loosely held s electron in the outermost valence shell of these elements makes them the most electropositive metals. They readily lose an electron to give monovalent M+ ions. Hence they are never found in the free or native state in nature.
Question 10.5 Explain why is sodium less reactive than potassium
As we know that in alkali metals, as we go down the group the atomic size increases and also the effective nuclear charge decreases. So, therefore, the outermost electron of potassium is easily removed. Electronic configuration of and electronic configuration of sodium (Na= ). Hence the reactivity of sodium is less than of potassium.
Question 10.6 Compare the alkali metals and alkaline earth metals with respect to (i) ionisation enthalpy (ii) basicity of oxides and (iii) solubility of hydroxides
(i) Ionisation enthalpy-
Alkali metals have low first IE as compare to alkaline earth metals because of having a large atomic size also after losing one electron they attain noble gas configuration. In alkaline earth metals, their first IE is higher then alkali metals because they have high effective nuclear charge and small in size as compare to group 1st element. However, they have low second IE as compare to alkali metals.
(ii) Basicity of oxides-
Alkali metal oxides are more basic than alkaline earth metal oxides. this is because alkali metals are highly electropositive which makes them highly ionic, so they readily dissociate into hydroxide ions in water than alkaline metals.
(iii) The solubility of Hydroxide-
Alkali metal hydroxide is more soluble in water than alkaline earth metals. This is because of the high lattice energy of alkaline earth metals.
Question 10.7 In what ways lithium shows similarities to magnesium in its chemical behaviour?
Chemical similarities between lithium and magnesium-
and slowly react with water and their hydroxide and oxides are also less soluble in water. On heating, their hydroxide decomposes. Both the element form nitride and by direct reaction with nitrogen.
and do not give superoxide on reacting with an excess of oxygen.
Lithium and Magnesium carbonates easily decompose into their oxides and carbon dioxide.
Chlorides of both element soluble in ethanol.
Both chlorides can crystallise from their aqueous solution as hydrates, and
Question 10.14 Why is decomposed at a lower temperature whereas at higher temperature?
As we go down the group the electropositive nature of alkali metals increases. And because of that, there is an increase of stability of carbonates. But carbonates of lithium is not stable because lithium carbonate is covalent. Lithium-ion is smaller in size so it can polarise the negative carbonate ion, leading to the formation of more stable lithium oxide. therefore, Lithium decomposes at the lower temperature while sodium carbonate decomposes at a higher temperature.
Question 10.15 Compare the solubility and thermal stability of the following compounds of the alkali metals with those of the alkaline earth metals. (a) Nitrates (b) Carbonates (c) Sulphates.
Alkali and alkaline earth metal nitrates are soluble in water. Down the group thermal stability of nitrates increases. Nitrates of alkaline and alkali metals give corresponding nitrites except for lithium nitrate, it gives lithium oxides.
[ M = Be, Mg, Ca, Sr, Ba]
Alkaline earth metal carbonates decompose on heating gives carbon dioxide and oxide. On the other hand carbonates of alkali metals are stable towards heat. The solubility of carbonates increases down the group in alkali metals (except ) . But carbonates of alkaline earth metals are insoluble in water.
thermal stability is good for both alkali and alkaline earth metals. Alkali metal sulphates are more soluble in water than alkaline earth metals. Solubility decrease down the group from to . sulphate of Be and Mg are readily soluble in water.
Question 10.16 Starting with sodium chloride how would you proceed to prepare (i) sodium metal (ii) sodium hydroxide (iii) sodium peroxide (iv) sodium carbonate ?
(i) Sodium metal can be extracted from sodium chloride.In this process electrolysis of fused (40%) and (60%) at a temp. of 1123K in Downs cell.
steel cathode and graphite block is act as anode. sodium and calcium deposit at cathode .
(ii) can be prepared by the electrolysis of sodium chloride. By Castner- kellner process. A brine solution is electrolysed using a mercury cathode and a carbon anode. Sodium metal discharged at the cathode combines with mercury to form sodium amalgam. Chlorine gas is evolved at the anode.
(iii) NaCl is electrolysed for the formation of Na metal (in downs process). this sodium metal is then heated on aluminium trays in air to form sodium peroxide.
(iv) Sodium carbonate is preapred by solvay process. is precipitated in a reaction of sodium chloride and ammonium hydrogen carbonate.
this crystals are heatedto give sodium carbonate.
Question 10.18 Describe two important uses of each of the following : (i) caustic soda (ii) sodium carbonate (iii) quicklime.
(i) Caustic Soda The chemical name is sodium hydroxide (). Sodium hydroxide is generally prepared commercially by the electrolysis of sodium chloride in Castner-Kellner cell.
the manufacture of soap, paper, artificial silk and a number of chemicals
in the purification of bauxite,
in the textile industries for mercerising cotton fabrics
for the preparation of pure fats and oils, and
as a laboratory reagent.
(ii) Sodium Carbonate-
The common name is washing soda ().Sodium carbonate is generally prepared by Solvay Process.
It is used in water softening, laundering and cleaning.
It is used in the manufacture of glass, soap, borax and caustic soda.
It is used in paper, paints and textile industries.
It is an important laboratory reagent both in qualitative and quantitative analysis
(iii) Quick lime-
The chemical name is calcium oxide and the formula is . It is prepared on a commercial scale by heating limestone (CaCO3) in a rotary kiln at 1070-1270 K ( )
It is an important primary material for manufacturing cement and is the cheapest form of alkali.
It is used in the manufacture of sodium carbonate from caustic soda.
It is employed in the purification of sugar and in the manufacture of dye stuffs.
Question 10.21 Describe the importance of the following : (i) limestone (ii) cement (iii) plaster of paris.
The chemical formula is .
Importance of limstone is-
It is used as a building material in the form of marble and in the manufacture of quick lime
Calcium carbonate along with magnesium carbonate is used as a flux in the extraction of metals such as iron.
It is also used as an antacid, mild abrasive in tooth paste, a constituent of chewing gum, and a filler in cosmetics.
Cement is an important building material. It is amixture of triclcium silicate() and tricalium aluminate().
Importance of cement-
It is used in concrete and reinforced concrete, in plastering and in the construction of bridges, dams and buildings
(iii) Plaster of Paris-
It is a hemihydrate of calcium sulphate. It is obtained when gypsum, , is heated to 393 K.
Importance of POP-
It is used in medicine as surgical bandages and also it is used for making casts and moulds.
Question 10.22 Why are lithium salts commonly hydrated and those of the other alkali ions usually anhydrous?
Lithium-ion is the smallest among the other alkali metal ions. Hence it has higher polarising power than others and so it can polarise water molecule more easily than other alkali metals. Hence the water molecules are more attracted towards Li salts as the water of crystallisation. Li+ has a maximum degree of hydration and for this reason, lithium salts are mostly hydrated, e.g., LiCl· 2H2O
As the down the group size of ions increase, their polarising power decreases. Hence other alkali metal ions usually form anhydrous salts.
Question 10.24 Explain the significance of sodium, potassium, magnesium and calcium in biological fluids
Significance of sodium potassium, magnesium and calcium in biological fluids-
It is mainly found in blood plasma and also in the interstitial fluid which surrounds the cell.
ions help in the transmission of nerve signals also for the regulating water in the plasma membrane.
Also for the transport of sugars and amino acids into the cells.
These ions are highly present within cell fluids.
Helps in activating many enzymes
To produce ATP it oxidises the glucose molecule.
Also helps in the transmission of nerve signals.
Magnesium and calcium-
Plays an important role in neuromuscular function (by magnesium), interneuronal transmission, cell membrane integrity and blood coagulation(by calcium)
Mg helps in maintains normal blood circulation in our body.
Question 10.29 How would you explain the following observations? (i) BeO is almost insoluble but BeSO4 is soluble in water, (ii) BaO is soluble but BaSO4 is insoluble in water, (iii) LiI is more soluble than KI in ethanol.
(i) is small in size so it has high polarising power and is also small in size. Compatibility of both the cation and anion are very high. So their lattice energy is also very high. When BeO is dissolved in water it's hydration energy is not sufficient to overcome its lattice energy. So, therefore, it is insoluble in water.
On the other hand, ions are large in size. Hence ion can easily polarise ions and making it unstable and because of that lattice energy of is not very high and so it is soluble in water.
(ii) is soluble because cation is large in size as compare to anion. Size compatibility between them is not good. Therefore is unstable. Hence lattice energy during the formation of their lattice is not high So it can be easily overcome by hydration energy. Therefore is soluble in water. In case of , we know that down the group hydration enthalpy decreases and both the anion and cation have very good size compatibility. So, lattice energy cannot be overcome by hydration energy. As a result, is not soluble in water.
(iii) The ion has high polarising power. It is very small in size as compare to ion. So, it has a high tendency to distort the electron cloud around the negative iodide () ion. As a result of high polarizability, it has high covalent character than. Hence it is more soluble in methanol.
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