Explore topic-wise InterviewSolutions in .

In potassium, the outer most electron is better shielded form the attractive force of the nucleus. It follows that this outermost electron is more easily lost than it is in sodium and potassium can be converted to ionic form more readily then sodium. Hence, sodium is less reactive than potassium.

NaOH is strong base, as it is completely hydrolysed in solution.

Plaster of paris is a hemihydrate of calcium sulphate (CaSO₄ . 1/2 H₂O). Plaster of paris is obtained by heating gypsum to 393K 

2 (CaSO₄.2H₂O)→ 2 (CaSO₄). H₂O + 3H₂O.

Alkali metals acquire, noble gas configuration after losing 1 electron, therefore their second ionization energy is higher than alkaline earth metals.

They are highly reactive, therefore, they occur in combined state and do not occur in free state.

Al occurs as oxide in nature as bauxite Al₂O₃. 2H₂O

d. K⁺ < Ca²⁺ < Mg²⁺ < Be²⁺

Calcium has great affinity for oxygen and nitrogen so it froms oxide surface. This coating protects calcium and keep it stable.

Calcium Carbonate, CaCO₃: 

It can be prepared by passing carbon dioxide through slaked lime or by the addition of sodium carbonate to calcium chloride. 

Ca (OH)₂ + CO₂ →  CaCO₃ + H₂O 

CaCl₂ + Na₂CO₃ → CaCO₃ + 2NaCl 

Excess of carbon dioxide should be avoided since this leads to the formation of water soluble calcium hydrogen carbonate. 

When heated to 1200 K, it decomposes to evolve carbon dioxide. 

CaCO₃ → CaO + CO₂ 

Uses: 

(i) It is used as a building material in the form of marble and in the manufacture of quick lime. 

(ii) Calcium carbonate along with magnesium carbonate is used as a flux in the extraction of metals such as iron.

Calcium Oxide or Quick Lime, CaO: 

It is prepared on a commercial scale by heating limestone (CaCO₃) in a rotary kiln at 1070-1270 K. 

CaCO₃ -----> CaO + CO₂

Uses: 

(i) It is an important primary material for manufacturing cement and is the cheapest form of alkali. 

(ii) It is used in the manufacture of sodium carbonate from caustic soda.

Calcium Hydroxide (Slaked lime), Ca (OH)₂

Calcium hydroxide is prepared by adding water to quick lime, CaO. The aqueous solution is known as lime water and a suspension of slaked lime in water is known as milk of lime. 

When carbon dioxide is passed through lime water it turns milky due to the formation of calcium carbonate. 

Ca (OH)₂ + CO₂ → CaCO₃+ H₂O 

On passing excess of carbon dioxide, the precipitate dissolves to form calcium hydrogen carbonate. 

CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂ 

Milk of lime reacts with chlorine to form hypochlorite, a constituent of bleaching powder. 

2Ca(OH)₂ + 2Cl₂ → Ca(OCl)₂ + CaCl₂ +2H₂O

Uses: 

(i) It is used in the preparation of mortar, a building material. 

(ii) It is used in white wash due to its disinfectant nature.

(a) 

(i) It is used in the building material in the form of mortar. 

(ii) It is used in the manufacture of bleaching powder. 

(iii) It is used in glass making and the purification of sugar. 

(iv) It is used to absorbed acidic gases.

(b) 

1. NH₄Cl + NaOH → NaCl + NH₄OH 

2. 2NaOH + CO₂ → Na₂CO₃ + H₂O

(i)  refining of petroleum 

(ii)  making paper and soaps

Step1: preparation of ammonical brine Ammonia is passed through a Saturated solution of sodium chloride in water , ammoniacal brine is formed .It is cooled to 30°C 

Step 2: carbonation Carbon dioxide gas is passed through ammoniacal brine ,where ammonium carbonate and sodiumbicarbonate.

NH₃ + H₂O + CO₂ → (NH₄)₂CO₃

(NH₄)₂CO₃ + H₂O + CO₂ → 2NH₄HCO₃

NH₄HCO₃ + NaCl → NH₄Cl + NaHCO₃.

Sodium bi carbonate crystal separates and these are heated to give sodium carbonate.

2NaHCO₃→ Na₂CO₃ + CO₂+H₂O

Step 3: Recovery of ammonia Ammonia is recovered when the solution containing ammonium chloride is treated with Ca(OH)₂.

2 NH₄Cl + Ca(OH)₂ → CaCl₂ + 2NH₃ + H₂O 

A brine solution is electrolyzed using a mercury cathode and a carbon anode .Sodium metal discharged at the cathode combines with mercury to form sodium amalgam.

2Na⁺ + 2e^- →2Na (reduction)

Na + Hg → Na-Hg (amalgam) 

Chlorine gas is evolved at the anode

2Cl^- → Cl₂ +2e^- (oxidation)

The mercury containing dissolved in sodium is sent to another chamber called decomposer, where sodium reacts with water forming sodium hydroxide and hydrogen. Decomposer is packed with graphite blocks as hydrogen is easily liberated over graphite surface. 

2Na-Hg +2H₂O → 2NaOH +H₂+2Hg 

The solution which flows out from decomposer is NaOH solution which is evaporated to dryness. 

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.

It is due to weak metallic bonds which is due to bigger atomic size that is why they how low melting and boiling points.

Alkali metals have only one valence electron per metal atom. As a result, the binding energy of alkali metal ions in the close-packed metal lattices are weak. Therefore, these are soft and have low melting point.

(i) Li has highest melting point. 

(ii) Cs has most electropositive character. 

(iii) li has lowest size of ion. 

(iv) Li has strongest reducing character.

In a period, melting points of alkali metals are lower than earth metals because alkali metals have weak metallic bond between them due to presence of only one valence electron.

When water is added to lime, it becomes hot and cracks to form a white powder. This process is called slaking of lime.

Since LiCl is covalent in nature. Li polarises Cl and due to polarization, its covalent character increases and therefore, LiCl is soluble in organic solvent.

(i) The decreasing order of hydration enthalpy is −Be²⁺ > Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺ 

(ii) A suspension of magnesium hydroxide in water is called milk of magnesia. It is used as antacid in medicine. 

(iii) Significance of Mg and Ca in biological fluids 

(a) All enzymes that utilize ATP in phosphate transfer require magnesium as the cofactor. 

(b) The main pigment is chlorophyll which contains magnesium. 

(c) About 99% of body calcium is present in bones and teeth which is essential for them. 

(d) Ca plays and important role in neuromuscular function, interneuron transmission, cell membrane integrity and blood coagulation.

Group I elements are called alkali metals because they form hydroxides on reaction with water which are strongly alkaline in nature.

Let, oxidation state of K = x

\(\therefore\) KO₂ Contains superoxide ion i.e., O₂^–

X + (-1) = 0

X – 1 = 0

X = +1

\(\therefore\) The oxidation state of K in KO₂ is +1

The anomalous behaviors of lithium is due to the following-

(i) Exceptionally small size of its atom and ion., Li⁺

(ii) High polarizing power (I, e; charge / radius radio)

d. Presence of fully filled 2s orbital

Na₂CO₃ is alkaline because it hydrolyses in water as follows:

Na₂CO₃ + 2H₂O → 2Na + + OH⁻ + H₂CO₃

When caesium and potassium metals are irradiated with light, light energy absorbed is sufficient to make an atom lose electron .Hence used as electrodes 

The members of the family combine with halogen to form corresponding halides which are ionic crystalline solids. Reactivity of alkali metals with particular halogen increases from Li to Cs. 

(i) Be (ii) Ca (iii) Be (iv) Be

Alkaline earth metals are called s – block elements because the last electron in their electronic configuration occupies the s – orbital of their valence shells.

Group 2 elements: Alkaline earth metals :

Atomic radii : The atomic radii of alkaline earth metals are fairly large though smaller than the corresponding alkali metals and they increase down the group. This is because on moving down the group, atomic radii increase primarily due to the addition of an extra shell of electrons in each succeeding element. 

Ionic radii: the atoms of these elements form divalent ions which show the same trend of increase in their size down the group.  

Ionization enthalpy: The alkaline earth metals have fairly low Ionizations enthalpies though greater than those of the corresponding elements of group 1 and this value decreases down the group. 

LiI + KF → LiF + KI

Larger cation stabilizes anion.

(i) Lithium is a very light metal; its density being 0.53 g cm^-3 which is less than any hydrocarbon solvent such as hexane, benzene, kerosene, etc. As a result, it will float on these solvents. That is why it is not kept in these solvents. Instead it is wrapped in grease or paraffin wax and placed as such in a bottle. 

(ii) Since lithium is the least dense metal its alloys with aluminum are much less dense than aluminum. Commercial alloys of lithium with aluminum contain a maximum of 2.45% by weight of lithium. Since w/W percentage of aluminum is much higher than that of lithium, therefore these are called Al-Li rather than Li-Al alloys. These alloys have a high tensile strength and hence are used in the construction of aeroplane frames. 

(i) Sodium ions are primarily found in the blood plasma and in the interstitial fluid which surrounds the cells while potassium ions are primarily present within the cell fluids. Sodium ions primarily help in the transmission of nerve signals, in regulating the flow of water across cell membranes and in the transport of sugars and amino acids into the cell. Thus sodium is found to be more useful than potassium. 

(ii) Potassium is important for healthy functioning of our heart, kidneys and other vital organs. Deficiency of potassium in diet causes heart diseases, high blood pressure, cancer, arthritis, digestive disorders and muscle cramps. The benefits of potassium are : 

It reduces blood pressure. 

Kidney stones are formulated by calcium being in the kidneys, the potassium prevents calcium from forming stones. The kidney filters the potassium and eliminates it in urine. 

Potassium helps in carrying oxygen to the brain and is important for healthy nerve functions. It is also good for relieving headache due to allergies. 

(iii) Potassium supplements should only be taken with the recommendation and supervision of the doctor since potassium does interact with other medicines. 

(iv) Some rich sources of potassium foods are: baked potatoes with skin, bananas, spinach, orange juice, tomato sauce, barley, beans, almonds etc.

Na⁺,K⁺ and Ca²⁺

Biological importance of Na and K are :

• Sodium ions participate in the transmission of nerve signals. 
• Sodium ions also regulate flow of water across the cell membranes and in transport of sugars and amino acids into the cells. 
• Potassium ions are the most abundant cations within cell fluids, where they activate many enzymes, participate in oxidation of glucose to produce ATP.
• Potassium ions in combination with sodium ions are responsible for transmission of nerve signals. 
• The functional features of nerve cells depend upon the sodium potassium ion gradient that is established in the cell.

KOH is the formulae of caustic potash.

Be resembles Al because charge over radius ratio is similar, i.e., they have similar polarizing power.

They have low ionisation energy and can lose electrons when light falls on them, that is why they are used in photoelectric cells.

Alkali metals have the lowest ionization energy in each period of the periodic table. Hence they emit electrons even when exposed to light. This phenomenon is called photoelectric effect. Rubidium and caesium are used in photoelectric cells.

Rock salt (NaCl), Na₂CO₃, NaHCO₃, 2H₂O (trona) are important ores of Na. Sylvine (KCl); 

KCl.MgCl₂.6H₂O (carnallite) are of K.

It results in the formation of intense blue colour solution which possess conduction power.

Na + (x + y)NH₃ → [Na(NH₃)_x⁺] + [e(NH₃)_y]⁻

CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂

It results in the formation of intense blue colour solution which possess conducting power.

We get amorphous sodium carbonate because it loses water molecules.

Beryllium is the least and barium is the most reactive.

Be < Mg < Ca < Sr < Ba

Calcium ion is responsible for clotting of blood in our body.

Li resembles Mg mainly due to similarity in sizes of their atoms and ions. The main points of similarity are: 

(1) Both are quite hard. 

(2) Both LiOH and Mg(OH)₂ are weak bases. 

(3) Carbonates of both on heating decompose to produce oxides and carbondioxide. 

(4) Both react with nitrogen to give ionic nitrides. 

(5) Nitrates of both decompose on heating to give oxides. 

(6) Both Li and Mg do not form solid bicarbonates. 

(7) Because of covalent character LiCl and MgCl₂ are soluble in ethanol. 

(8) The hydroxides, bicarbonates and fluorides of both Li and Mg are sparingly soluble in water.