i. The oxidation state shown by alkaline earth metals is
Answer: a) +2
Explanation: Alkaline earth metals (Group 2) have two electrons in their outermost s-orbital, which they readily lose to achieve a stable noble gas configuration, resulting in a +2 oxidation state.
ii. Which one of the following is the most soluble in water?
Answer: d) Ba(OH)₂
Explanation: The solubility of Group 2 hydroxides increases down the group. Barium hydroxide is the most soluble among the given options.
iii. Which of the following alkaline earth metal hydroxides is amphoteric in character?
Answer: a) Be(OH)₂
Explanation: Beryllium hydroxide is amphoteric, meaning it can react with both acids and bases. This is due to the small size and high charge density of the Be²⁺ ion.
iv. Of the metals Be, Mg, Ca and Sr of group 2 A, in the periodic table the least ionic chloride would be formed by
Answer: a) Be
Explanation: Beryllium has the highest charge density and the greatest tendency to form covalent bonds. Therefore, BeCl₂ is the least ionic (most covalent) chloride among the Group 2 elements.
v. The order of solubility of sulphates of alkaline earth metals in water is
Answer: a) Be > Mg > Ca > Sr > Ba
Explanation: The solubility of Group 2 sulfates decreases down the group. Beryllium sulfate is the most soluble, while barium sulfate is the least soluble (practically insoluble).
vi. The solubilities of carbonates decrease down the magnesium group due to a decrease in
Answer: a) hydration energies of cations
Explanation: As the size of the cation increases down the group, its hydration energy decreases significantly. The lattice energy also decreases but less rapidly. The decrease in hydration energy outweighs the decrease in lattice energy, leading to a decrease in solubility.
vii. In which of the following the hydration energy is higher than the lattice energy?
Answer: a) MgSO₄
Explanation: For MgSO₄, the small Mg²⁺ ion has a very high hydration energy, which is greater than its lattice energy. This makes the dissolution process exothermic and the salt highly soluble. For the heavier sulfates, lattice energy dominates, making them less soluble.
viii. Which of the following alkaline earth metal sulphates has hydration enthalpy higher than the lattice enthalpy?
Answer: c) BeSO₄
Explanation: BeSO₄ has the highest hydration enthalpy among the Group 2 sulfates due to the very small size of the Be²⁺ ion. Its hydration enthalpy is higher than its lattice enthalpy, making it the most soluble.
ix. Which gas is released when CaCO₃ reacts with dilute HCl?
Answer: c) CO₂
Explanation: Carbonates react with dilute acids to produce carbon dioxide gas, water, and a salt. CaCO₃ + 2HCl [source symbol unavailable] CaCl₂ + H₂O + CO₂.
x. Brick red is characteristics flame colour of
Answer: c) Calcium
Explanation: Calcium compounds impart a brick-red color to a flame. Barium gives an apple-green color, and strontium gives a crimson-red color.
i. Describe and explain the trend observed in the thermal stabilities of the carbonates of Group II.
Answer: The thermal stability of Group II carbonates increases down the group from BeCO₃ to BaCO₃. This is because the polarizing power of the cation decreases as its size increases. Smaller cations (like Be²⁺) polarize the carbonate ion more effectively, weakening the C-O bond and facilitating decomposition at lower temperatures. Larger cations (like Ba²⁺) have less polarizing power, so higher temperatures are needed to decompose their carbonates.
ii. Describe the use of Group II elements or its compounds in agriculture.
Answer: Group II elements and their compounds have several agricultural uses:
Calcium: Lime (CaO) and limestone (CaCO₃) are used to neutralize acidic soils, raising the pH to optimal levels for crop growth. Magnesium: Magnesium sulfate (Epsom salts) is used as a fertilizer to correct magnesium deficiency in plants, which is essential for chlorophyll formation. Calcium: Calcium is essential for plant cell wall structure and is added as gypsum (CaSO₄·2H₂O) to improve soil structure.
iii. Write an equation to represent the thermal decomposition of calcium nitrate.
Answer: 2Ca(NO₃)₂(s) [source symbol unavailable] 2CaO(s) + 4NO₂(g) + O₂(g)
iv. Why are the elements of Group 2 called alkaline earth metals?
Answer: Group 2 elements are called "alkaline earth metals" because their oxides and hydroxides are alkaline (basic) in nature. The term "earth" was historically used by alchemists to refer to non-metallic substances that were insoluble in water and resistant to heat, like the oxides of these metals. Hence, the name "alkaline earth metals" was adopted.
v. How do group 1 metals differ from Group 2 metals?
Answer:
| Feature | Group 1 (Alkali Metals) | Group 2 (Alkaline Earth Metals) |
| Valence Electrons | 1 | 2 |
| Oxidation State | +1 | +2 |
| Reactivity | More reactive | Less reactive than Group 1 |
| Hardness | Soft, can be cut with a knife | Harder, but still soft |
| Density | Lower | Higher |
| Flame Color | Characteristic colors | Characteristic colors |
| Hydroxide Solubility | Increases down the group | Increases down the group |
vi. Explain with the help of an equation the amphoteric nature of beryllium oxide.
Answer: Beryllium oxide (BeO) is amphoteric, meaning it reacts with both acids and bases.
With Acid: BeO(s) + 2HCl(aq) [source symbol unavailable] BeCl₂(aq) + H₂O(l) With Base: BeO(s) + 2NaOH(aq) [source symbol unavailable] Na₂BeO₂(aq) + H₂O(l) This dual behavior is due to the small size and high polarizing power of the Be²⁺ ion.
vii. Explain qualitatively the variation in solubility of the hydroxides of the elements in Group II down the Group from magnesium to barium.
Answer: The solubility of Group II hydroxides increases down the group from Mg(OH)₂ to Ba(OH)₂. This trend can be explained by the relative magnitudes of lattice energy and hydration energy. As the cation size increases down the group, both lattice energy and hydration energy decrease. However, the lattice energy decreases more rapidly than the hydration energy. Therefore, the net energy change for dissolution becomes more favorable (less endothermic or more exothermic) down the group, leading to increased solubility.
i. Explain the reactivity of group II elements with water and dilute HCl with chemical reactions.
Answer: The reactivity of Group II elements with water and dilute HCl increases down the group from Beryllium to Barium. This trend is due to the decreasing ionization energy and increasing metallic character down the group.
Reaction with Water:
Beryllium: Does not react with water or steam, even at high temperatures, due to a protective oxide layer. Magnesium: Reacts very slowly with cold water but reacts vigorously with steam to form magnesium oxide and hydrogen gas.
Mg(s) + H₂O(g) [source symbol unavailable] MgO(s) + H₂(g)
Calcium, Strontium, Barium: React with cold water to form the corresponding hydroxide and hydrogen gas. The reaction becomes increasingly vigorous down the group.
Ca(s) + 2H₂O(l) [source symbol unavailable] Ca(OH)₂(aq) + H₂(g) Sr(s) + 2H₂O(l) [source symbol unavailable] Sr(OH)₂(aq) + H₂(g) Ba(s) + 2H₂O(l) [source symbol unavailable] Ba(OH)₂(aq) + H₂(g)
Reaction with Dilute HCl: All Group II elements react with dilute hydrochloric acid to form the corresponding chloride and hydrogen gas. The reaction becomes more vigorous down the group.
Mg(s) + 2HCl(aq) [source symbol unavailable] MgCl₂(aq) + H₂(g) Ca(s) + 2HCl(aq) [source symbol unavailable] CaCl₂(aq) + H₂(g) Ba(s) + 2HCl(aq) [source symbol unavailable] BaCl₂(aq) + H₂(g)
In summary, the reactivity of Group II elements with water and acids increases down the group due to decreasing ionization energy.
ii. Analyse the trends in the thermal stability of nitrates and carbonates of alkaline earth metals.
Answer: The thermal stability of both nitrates and carbonates of Group II elements increases down the group from Beryllium to Barium.
Thermal Stability of Carbonates:
Trend: BeCO₃ < MgCO₃ < CaCO₃ < SrCO₃ < BaCO₃
Explanation: The thermal stability depends on the polarizing power of the cation. Small, highly charged cations (like Be²⁺) polarize the large carbonate ion (CO₃²⁻) more effectively, weakening the C-O bond. This facilitates the decomposition of the carbonate into the oxide and carbon dioxide at lower temperatures. As the cation size increases down the group, its polarizing power decreases, and the carbonate becomes more stable. Example: BaCO₃ requires a much higher temperature to decompose than BeCO₃.
Thermal Stability of Nitrates:
Trend: Be(NO₃)₂ < Mg(NO₃)₂ < Ca(NO₃)₂ < Sr(NO₃)₂ < Ba(NO₃)₂
Explanation: A similar explanation applies. The smaller cations polarize the nitrate ion (NO₃⁻) more effectively, leading to decomposition at lower temperatures. The decomposition products are the oxide, nitrogen dioxide, and oxygen. Example: 2Ca(NO₃)₂(s) [source symbol unavailable] 2CaO(s) + 4NO₂(g) + O₂(g)
In summary, the thermal stability of both carbonates and nitrates of Group II elements increases down the group due to the decreasing polarizing power of the cation.
1. What is the general trend in the melting points going down Group 2?
Answer: The melting points of Group 2 elements generally decrease down the group. This is because as the atomic size increases, the metallic bond strength decreases (the delocalized electrons are further from the nuclei), requiring less energy to break the bonds. However, there is a slight increase from Mg to Ca due to changes in crystal structure.
2. Explain why the atoms in Group 2, as in any other group, get larger with increasing atomic number.
Answer: Atomic size increases down a group because new electron shells are added. Each new period adds a principal energy level. Although the nuclear charge also increases, the shielding effect of the inner electrons outweighs the increased nuclear attraction, causing the outermost electrons to be further from the nucleus, thus increasing the atomic radius.
3. Write a balanced chemical equation, including state symbols, for the reaction of:
i. strontium with oxygen
Answer: 2Sr(s) + O₂(g) [source symbol unavailable] 2SrO(s)
ii. strontium oxide with hydrochloric acid.
Answer: SrO(s) + 2HCl(aq) [source symbol unavailable] SrCl₂(aq) + H₂O(l)
4. Barium reacts vigorously when added to water.
i. Write a balanced chemical equation, including state symbols, for the reaction of barium with water.
Answer: Ba(s) + 2H₂O(l) [source symbol unavailable] Ba(OH)₂(aq) + H₂(g)
ii. State two observations that could be made during this reaction.
Answer: (1) The barium metal fizzes/moves rapidly on the surface of the water. (2) Bubbles of hydrogen gas are evolved.
iii. Suggest the approximate pH of the resulting solution.
Answer: The resulting solution is basic (barium hydroxide). The pH would be approximately 12-14.
iv. Will the reaction be more or less vigorous than the reaction of barium with water? Explain your answer.
Answer: (Assuming the question meant "magnesium with water") The reaction of barium with water is more vigorous than magnesium with water. Barium is lower down Group 2 and has a lower ionization energy, making it more reactive. Magnesium reacts very slowly with cold water.
5. Describe what you would see when magnesium reacts with cold water and steam. Also write an equation for the reaction with steam.
Answer:
With Cold Water: Very slow reaction. A few bubbles of hydrogen gas may form on the surface of the magnesium. With Steam: The magnesium ribbon glows brightly, and a white solid (magnesium oxide) is formed. Hydrogen gas is evolved. Equation: Mg(s) + H₂O(g) [source symbol unavailable] MgO(s) + H₂(g)
1. Which one of the three compounds listed will decompose at the lowest temperature?
i. Calcium carbonate, strontium carbonate, barium carbonate
Answer: Calcium carbonate will decompose at the lowest temperature. Thermal stability increases down the group (Ca < Sr < Ba).
ii. Barium nitrate, calcium nitrate, magnesium nitrate
Answer: Magnesium nitrate will decompose at the lowest temperature. Thermal stability increases down the group (Mg < Ca < Ba).
2. Write a balanced chemical equation, including state symbols, for the thermal decomposition of:
i. Strontium carbonate
Answer: SrCO₃(s) [source symbol unavailable] SrO(s) + CO₂(g)
ii. Barium nitrate.
Answer: 2Ba(NO₃)₂(s) [source symbol unavailable] 2BaO(s) + 4NO₂(g) + O₂(g)
Explain why magnesium sulphates is more soluble than barium sulfate by referring to the relative values of the lattice energies and enthalpy changes of hydration.
Answer: The solubility of a salt depends on the balance between its lattice energy (energy required to break the ionic lattice) and its hydration energy (energy released when ions are hydrated).
Magnesium Sulfate (MgSO₄): The Mg²⁺ ion is small and has a high charge density, resulting in a very high hydration energy. Although its lattice energy is also high, the hydration energy is sufficient to overcome it, making the dissolution process energetically favorable (exothermic) and the salt highly soluble. Barium Sulfate (BaSO₄): The Ba²⁺ ion is large, so its hydration energy is much lower. However, the lattice energy remains relatively high because of the strong electrostatic attraction between Ba²⁺ and SO₄²⁻. The lattice energy is greater than the hydration energy, making the dissolution process endothermic and the salt practically insoluble.
In summary, MgSO₄ is more soluble because its hydration energy is higher than its lattice energy, while for BaSO₄, the lattice energy is higher than the hydration energy.
1. Why beryllium form complex compounds?
Answer: Beryllium forms complex compounds because of its small size and high charge density (high polarizing power). The Be²⁺ ion has a strong tendency to attract electron pairs from ligands (e.g., water, ammonia, chloride ions). This allows it to form coordinate covalent bonds, leading to the formation of complex ions such as [Be(H₂O)₄]²⁺ or [BeCl₄]²⁻. This is a characteristic of small, highly charged cations.
2. Starting from calcium carbonate how would you extract pure calcium metal.
Answer: To extract pure calcium metal from calcium carbonate:
1. Thermal Decomposition: Heat calcium carbonate to produce calcium oxide (quicklime).
CaCO₃(s) [source symbol unavailable] CaO(s) + CO₂(g)
2. Electrolysis: Calcium metal is obtained by the electrolysis of molten calcium chloride (CaCl₂), which is obtained by reacting CaO with HCl.
CaO(s) + 2HCl(aq) [source symbol unavailable] CaCl₂(aq) + H₂O(l) Electrolysis of molten CaCl₂: Ca²⁺ + 2e⁻ [source symbol unavailable] Ca (at cathode); 2Cl⁻ [source symbol unavailable] Cl₂ + 2e⁻ (at anode). The calcium metal is deposited at the cathode.
