We are going to prepare s- s-block elements which are alkali and alkaline earth metals through notes and quizzes. Learning your chapter through quizzes is a wonderful way of preparation.
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Quiz [Set 1] S- Block Elements (you can learn all mcqs by practice more and more)
Quiz [Set 2] S- Block Elements (you can learn all mcqs by practice more and more)
Quiz [Set 3] S- Block Elements (you can learn all mcqs by practice more and more)
Short questions from class 12 (Alkali and alkaline earth metals)
Q.1 Why the elements of group I-A are called alkali metals?
The name alkali is derived from the Arabic word that means “ashes”. Actually, metals like Na and K etc. are present in the ashes of plants. They produce a strongly alkaline solution in water.
Q.2 Why the elements of group II-A are called alkaline earth metals?
The word alkaline means that they produce Alkalies in water. Moreover, they are widely distributed in the earth’s crust, so are called alkaline earths.
ORES AND MINERALS OF GROUP I-A
Q.3 What are the most abundant elements among the alkali metals in the earth’s crust?
Sodium and potassium are the most abundant among the alkali metals. Each of them contributes about 2.4 % of the earth’s crust.
Q.4 Why the alkali metals are not found free in nature?
Alkali metals are very reactive. They have strong tendencies to make compounds by reacting with other elements. So, they are not found free in nature but in the form of ores and minerals.
Q.5 What are the important ores and minerals of sodium?
Sodium is found in the form of
- Rock salt (Halite) NaCl
- Chile saltpeter NaNO3
- Natron Na₂CO3. H₂O
- Trona Na₂CO3, 2NaHCO3.2H₂O
- Borax Na₂B₂O7. 10H₂O
Q.6 What are the important ores and minerals of potassium?
The important ores and minerals of potassium are
Carnallite KCI. MgCl2. 6H₂O
Sylvite KCI
Alumite (alum stone) K₂SO4. Al₂(SO4)3.4Al(OH)3.
Q.7 Why the melting and boiling points of group I-A and II-A decrease down the group?
The sizes increase down the group and due to decreasing polarizabilities, their forces of attraction decrease. It decreases the melting and boiling points.
Q.8 Why the alkali metals are strong reducing agents?
The alkali metals have low ionization energy values, so they can give electrons to other species very easily. In other words, they can decrease the oxidation number of other species and can act as reducing agents.
Q.9 Why the alkaline earth metals are reducing agents, but less reducing than those of group I-A?
Elements of group II-A have low ionization potentials but are greater than I-A. They can give electrons to other species, but not as efficiently as I-A. This is due to smaller sizes and greater nuclear charges.
Q.10 What are the flame tests of alkali metals?
Lithium shows crimson red, sodium golden yellow, potassium violet, while rubidium and caesium also show violet flame tests.
Q.11 The compounds of alkali and alkaline earth metals are colourless, but some of them are coloured. Give reason:
Ans: Alkali and alkaline earth metals are s-block elements that mostly do not show the colours in their compounds. d-block elements show the colours. The compounds like KMnO, and K₂Cr₂O, show the colour due to Mn and Cr, but not due to K and oxygen.
Q.12 Lithium only gives a simple oxide with oxygen, but sodium and potassium give peroxide and superoxide. Why?
The formation of peroxide and superoxide is due to the greater reactivity of alkali metals. Since Na and K are more reactive than Li so they should give normal oxides, peroxides and superoxides.
Q.13 When sodium reacts with water, the hydrogen which evolves catches fire, Why?
The reaction of sodium with water is very fast and highly exothermic. The heat evolved compels hydrogen gas from the reaction to react with the oxygen of the atmosphere. This burning of hydrogen with oxygen is the fire.
Q.14 Why the ionic hydrides are very good reducing agents?
Ionic hydrides release H+ in the solution which combines with other species to give its electrons and so it reduces the others. NaH ⇆ Na+ + H–
Abnormal Behaviour Of Lithium in Its Group
Q.15 Which element of group I-A reacts with nitrogen and carbon?
Lithium is the only I-A group element that combines with nitrogen and carbon to give a nitride and a carbide
6Li + N₂ → 2Li3N
4Li + C → Li4C
Q.16 Why does lithium differ from its own family members?
(i) Li and Li+ have very small sizes.
(ii) Li has a high charge density and high polarizing power.
(iii) The ionization energy and electronegativity of Li are very high as compared to others.
Q.17 Which salts of lithium are insoluble in water, but corresponding salts of other alkali metals are water-soluble?
LiOH, LiF, Li2CO3, and Li3PO4, are insoluble in water. Anyhow, hydroxide, fluorides, carbonates and phosphates of other alkali metals are water-soluble.
Q.18 What is the effect of heat on hydroxides of alkali metals?
The hydroxides of alkali metals are LiOH, NaOH, KOH etc. They are all stable towards heat and this stability increases down the group.
Q.19 How do you compare the carbonate of lithium with the carbonates of other family members?
Li2CO3 is sensitive to high temperatures and decomposes on heating.
Li2CO3 → Li2O + CO₂
But the carbonates of other alkali metals are stable towards heat.
Q.20 How do you compare LiNO3 with nitrates of other alkali metals?
LiNO3 on heating decomposes to give Li2O and NO2 gas. The nitrates of sodium give NaNO₂ and oxygen.
4LiNO3 → Li2O+4NO₂ + O₂
2NaNO3 → 2NaNO₂ + O₂
ORES AND MINERALS OF GROUP II-A
Q.21 Give the names and formulas for common minerals of beryllium.
Beryllium has two important minerals:
- Beryl Be3Al2(SiO3)6
- Chrysoberyl Al2BeO4
Q.22 Give the names and formulas for the common minerals of magnesium.
Some important minerals of magnesium are as follows:
- Magnesite MgCO3
- Dolomite MgCO3.CaCO3
- Carnallite KCI. MgCl₂ 6H₂O
- Epsom salt MgSO4. 7H2O
- Soap stone (talc) H₂Mg3.(SiO3)4.7H₂O
- Asbestos CaMg3.(SiO3)4
Q.23 Give the names and formulas for common minerals of calcium
Some important minerals of calcium are:
- Calcite (lime stone) CaCO3
- Gypsum CaSO4.2H₂O
- Fluorite CaF₂
- Phosphorite Ca3(PO4)2
PHYSICAL AND CHEMICAL PROPERTIES OF GROUP II-A
Q.24 Heat of hydration of alkaline earth metals go on decreasing from top to bottom in the periodic table. Why?
The atomic and ionic sizes go on increasing from top to the bottom in periodic table. The charge densities decrease down the group. So, the heat of hydration decreases down the group.
Q.25 Mention the flame test of II-A group elements:
Beryllium and magnesium do not show any colour to the flame. Calcium shows brick red, strontium shows crimson, barium shows apple green and radium shows red colour.
Q.26 How do you compare the polarizing powers of ions of II-A and that of I-A group elements?
The first members of I-A and II-A i.e. Li and Be have high polarizing powers due to greater charge densities and smaller sizes. The polarizing powers decrease down the group in both cases i.e. I-A and II-A. Anyhow, ions of II-A are better polarizers.
Q.27 How do magnesium and calcium react with nitrogen to give nitrides which on hydrolysis give ammonia?
The reactions are as follows: 3Mg + N₂ → Mg3N₂
3Ca+ N₂ → Ca3N₂
Mg3N2 + 6H₂O → 3Mg(OH)₂ + 2NH₂
Ca3N₂ + 6H₂O → 3Ca(OH)₂ + 2NH3
COMPOUNDS OF GROUPS I-A AND II-A
Q.28 How do you discuss the effects of heat on the carbonates of group I-A and II-A?
The carbonates of the I-A group are stable towards heat except Li₂CO3 which decomposes to give CO₂ just like the carbonates of alkaline earth metals.
Li₂CO3 + heat → Li₂O + CO₂
CaCO3 + 900 °C → CaO+CO3
Q.29 Why does beryllium differ from its own family members?
(1) It has very small size as compared to other family members.
(ii) It has very high electronegativity.
Q.30 How do you compare the carbide of beryllium with carbide of calcium?
Be2C reacts with water to give CH4 while CaC2 reacts with water to give C2H2
Be2C + 4H₂O → 2Be(OH)2 +CH4
CaC2 + 2H2O →Ca(OH)2 + C₂H₂
Q.31 What is the trend of changing basicity of oxides down the group?
In all the groups, the basic characters of oxides increase down the group. Li2O is less basic than Na2O. Similarly, BeO is amphoteric while the oxides of Mg, Ca, Sr and Ba are basic.
Q.32 How does beryllium react with NaOH to give a salt and evolve hydrogen?
Beryllium is the only member of II-A group elements which reacts with alkalies to give hydrogen Be + 2NaOH → Na2BeO₂ + H₂
Q.32 BeO is an amphoteric oxide. Justify it.
BeO + H₂SO4 → BeSO4 + H₂O
BeO+2NaOH → Na₂BeO₂ + H₂O
Q.33 How KO2 can be used by mountaineers?
Actually, KO₂ reacts with CO2 to give K₂CO3 and oxygen. So KO2 can be used in breathing equipment for mountaineers because KO2 absorbs CO₂ released by the mountaineers and releases oxygen at the same time.
Q.34 Why the aqueous solution of Na2CO3 is alkaline in nature.
Na2CO3 is a salt made from a weak acid and a strong base. It undergoes hydrolysis to give NaOH and H₂CO3. NaOH is a strong base, but H₂CO3 is a weak acid. So, the solution is alkaline.
Na₂CO3 + 2H₂O → 2NaOH + H₂CO3
Q.35 What is the trend of the solubilities of oxides of alkaline earth metals?
The solubilities of oxides of alkaline earth metals increase down the group and they are converted into hydroxide. BeO and MgO are insoluble in water.
CaO+H₂O → Ca(OH)2
SrO + H₂O → Sr(OH)2
BaO+H₂O → Ba(OH)2
Q.36 How do you compare the solubilities of hydroxide of alkaline earth metals?
Be(OH)2 and Mg(OH)2 are insoluble in water. The hydroxides of other metals are slightly soluble. The solubilities increase down the group.
Q.37 What is lime and lime water?
The formula of lime is CaO. When it is dissolved in water it gives Ca(OH)₂ which is called lime water. Lime is found in the solid state whereas the latter is in the liquid state.
Q.38 What is the milk of magnesia and what is its use?
Milk of magnesia is the suspension of Mg(OH)₂ in water. It is used for the treatment of acidity in stomach.
SODA ASH
Q.39 What is the effect of temperature on Na₂CO3?
Na₂CO3 is stable towards heat just like the carbonates of other alkali metals except for Li2CO3 which decomposes to give Li₂O and CO₂.
Q.40 What is the difference between soda ash and washing soda?
Anhydrous Na₂CO3 is called soda ash while decahydrate (Na₂CO3. 10H₂O) is called washing soda. They are both prepared by Solvay’s process.
LIME WATER
Q.41 What happens when CO₂ gas is passed through lime water?
Lime water turns milky and CaCO3 is produced in the lime. CaCO3 is water-insoluble so the white suspension is produced and we say that solution of lime turns milky.
Ca(OH)₂ + CO₂ →CaCO3+ H₂O
Q.42 What happens when excess CO₂ is passed through lime water?
Excess CO₂ converts CaCO3 to Ca(HCO3)2. It is water-soluble. So milkiness of the lime water disappears.
Q.43 Why the lime water turns white after white wash on the walls?
Lime water is Ca(OH)2. It reacts with CO₂ of the air and converts it into CaCO3 which is a white solid.
NITRATES AND SULPHATES
Q.44 In what respects nitrates of Li, Mg and Ba are related with each other?
They all decompose on heating to give metal oxides and NO₂ gas
4LiNO3 → 2Li₂O + 4NO₂+0₂
2Mg(NO3)2 → 2MgO + 4NO₂ + O₂
2Ba(NO3)2 → 2BaO + 4NO₂ + 0₂
Q.45 How do you compare the solubilities of sulphates of alkaline earth metals?
BeSO4 and MgSO4 are fairly water soluble. CaSO4 is slightly soluble in water. SrSO4 and BaSO4 are totally water insoluble.
Q.46 What is gypsum and how it is related with plaster of Paris?
Gypsum is CaSO4. 2H₂O. When it is heated a little bit above 100°C, then half hydrate is produced which is called plaster of Paris
2CaSO4.2H₂O → (CaSO4)2.H₂O + 3H₂O
COMMERCIAL PREPARATION OF NaOH
Q.47 What are the advantages of Down’s cell for the preparation of sodium on commercial scale?
Metallic fog is not produced. Liquid sodium can be easily collected at 600°C. The material of the cell is not attacked by the products during electrolysis.
Q.48 Why CaCl₂ is added in molten NaCl in Down’s cell?
CaCl₂ lowers the melting point of NaCl upto 600°C. In this way, fuel is saved and the plant gets the longer life due to working at low temperature.
Q.49 Which substances are deposited at cathode and anode in the Nelson’s cell?
Hydrogen is collected at the cathode. Sodium is also collected at the cathode but reacts with water to give caustic soda. Chlorine is deposited at the anode.
GYPSUM AND PLASTER OF PARIS
Q.50 What is the importance of Sulphur for the plants?
Sulphur affects the growth of the plants and becomes the part of some of the proteins. It influences the chlorophyll development and improves the roots of the plants.
Q.51 Why the plaster of Paris is called half hydrate?
The formula of plaster of Paris is (CaSO4)2 H₂O or CaSO4. 1/2H₂O. It means that for one molecule of CaSO4 half water molecule is present in the crystal structure.
Q.52 What do you mean by setting of plaster of Paris?
Plaster of Paris sets to a hard mass when it is mixed with half of its weight of water. It sets to a hard-porous mass. It becomes hydrated within 10 – 15 minutes and one percent increase of volume takes place.
Q.53 What are the main uses of plaster of Paris?
Plaster of Paris is used,
- for making plaster walls.
- cast of statuary.
- making coins
- surgery
Q.54 What is hard finish plaster?
Those plasters which are made by the calcination of anhydrous sulphate with alum or borax are called hard finish plasters. They set very slowly but give a hard finish.
Q.55 What is the use of material which is produced when the plaster of Paris is mixed with wood pulp?
A material is obtained which is used for the construction of buildings. This is also used as wall boards and for the purpose of partition.
Q.56 What is the role of gypsum in cement industry?
The clinker obtained from the rotary kiln is ground to a fine powder and mixed with 2 % gypsum. The cement so produced does not harden so rapidly. It decreases the setting time of cement.
Q.57 What do you mean by dead burnt gypsum?
When gypsum is heated at high temperature, it becomes completely anhydrous. When water is mixed with anhydrous CaSO4, then it does not set to a hard mass. So, it is called dead burnt gypsum.
Q.58 What is the function of calcium in plant growth?
Calcium improves the entire root system and leaves development. It increases the activity of the micro-organisms. Calcium manages the supply of available phosphorus from the soil to the plants.
LIME
Q.59 Indicate the processes in which lime acts as dehydrating reagent.
Lime is used for drying the ammonia gas. It is also used to remove 5% water from azeotropic mixture of commercial alcohol. Soda lime which is a mixture of NaOH and Ca(OH)2 can remove water and CO₂ from certain gases.
Q.60 What is lime mortar? Give equations for its hardening.
It is prepared by mixing lime with the sand and water. A thick paste is obtained and when placed between the stones and bricks, binds them together. The reactions are as follows:
CaO +H2O → Ca(OH)₂ + CO₂
Ca(OH)₂ + CO₂ → CaCO3 + H₂O
Ca(OH)₂ + SiO₂ → CaSiO3 + H₂O
