Group 2, The Alkaline Earth Metals

Which element in Group 2 has the highest atomic number?

• Radium

• Magnesium

• Calcium

• Barium

Answer explanation

Radium is the element in Group 2 with the highest atomic number, which is 88. In comparison, magnesium (12), calcium (20), and barium (56) have lower atomic numbers.

Explain the trends in atomic radius and first ionisation energy of the elements Mg–Ba.

Answer explanation

In the Mg–Ba group, atomic radius increases down the group due to added electron shells. Conversely, first ionisation energy decreases as the outer electrons are further from the nucleus and experience greater shielding, making them easier to remove.

Explain the melting point of the elements Mg–Ba in terms of their structure and bonding.

• The melting point generally decreases down the group due to weaker metallic bonding as the atomic size increases.

• The melting point generally increases down the group due to stronger covalent bonding as the atomic size increases.

• The melting point remains constant down the group because the number of delocalized electrons does not change.

• The melting point increases down the group due to increased van der Waals forces between atoms.

Answer explanation

The melting point of Mg–Ba decreases down the group because as atomic size increases, the metallic bonding weakens due to the greater distance between positive ions and delocalized electrons, leading to lower melting points.

What are the reactions of the elements Mg–Ba with water?

Answer explanation

The elements Mg–Ba react with water, forming hydroxides and releasing hydrogen gas. The reactivity increases down the group, with Ba reacting more vigorously than Mg.

What is the use of magnesium in the extraction of titanium from TiCl4?

• Magnesium is used as a reducing agent to extract titanium from titanium(IV) chloride (TiCl4).

• Magnesium is used as a catalyst in the extraction process.

• Magnesium is used to oxidize titanium(IV) chloride (TiCl4).

• Magnesium is used to purify titanium after extraction.

Answer explanation

Magnesium acts as a reducing agent in the extraction of titanium from titanium(IV) chloride (TiCl4), facilitating the conversion of TiCl4 to titanium metal.

Which of the following is sparingly soluble in water?

• Mg(OH)2

• Ca(OH)2

• Ba(OH)2

• Sr(OH)2

Answer explanation

Mg(OH)2 is sparingly soluble in water, while Ca(OH)2, Ba(OH)2, and Sr(OH)2 are more soluble. This lower solubility of Mg(OH)2 is due to its higher lattice energy compared to the other hydroxides.

What is the use of Ca(OH)2 in agriculture?

Answer explanation

Ca(OH)2, or calcium hydroxide, is used in agriculture to improve soil pH, making it less acidic. This enhances nutrient availability for plants, promoting better growth and crop yields.

What is the use of CaO or CaCO3 in relation to flue gases?

• CaO or CaCO3 is used to remove SO2 from flue gases.

• CaO or CaCO3 is used to increase CO2 in flue gases.

• CaO or CaCO3 is used to cool down flue gases.

• CaO or CaCO3 is used to add moisture to flue gases.

Answer explanation

CaO and CaCO3 are effective in removing SO2 from flue gases through a chemical reaction, forming calcium sulfite or sulfate, thus reducing sulfur dioxide emissions and improving air quality.

Which of the following is insoluble in water?

• MgSO4

• CaSO4

• BaSO4

• SrSO4

Answer explanation

BaSO4 (barium sulfate) is insoluble in water, while MgSO4, CaSO4, and SrSO4 have varying degrees of solubility. BaSO4's low solubility makes it the correct choice for this question.

Why is acidified BaCl2 solution used to test for sulfate ions and why is it acidified?

• Acidified BaCl2 is used to test for sulfate ions because it reacts with sulfate ions to form a white precipitate of BaSO4. It is acidified to prevent interference from other ions such as carbonate.

• Acidified BaCl2 is used to test for sulfate ions because it enhances the color of the solution. It is acidified to increase the solubility of BaSO4.

• Acidified BaCl2 is used to test for sulfate ions because it prevents the formation of any precipitate. It is acidified to neutralize the solution.

• Acidified BaCl2 is used to test for sulfate ions because it reacts with chloride ions to form a white precipitate. It is acidified to remove excess sulfate ions.

Answer explanation

Acidified BaCl2 is used to test for sulfate ions because it reacts with sulfate ions to form a white precipitate of BaSO4. It is acidified to prevent interference from other ions such as carbonate.