9701 · 10.1
Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds flashcards
Revision flashcards for Cambridge 9701 Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds (syllabus 10.1). Flip, recall, then mark a real past-paper question.
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What is the general trend in first ionisation energy down Group 2?
It decreases. The increasing atomic radius and shielding effect outweigh the increase in nuclear charge, making it easier to remove the outermost electron.
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How does reactivity with water change down Group 2?
Reactivity increases. Magnesium reacts very slowly with cold water, calcium reacts readily, strontium reacts vigorously, and barium reacts rapidly.
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Write the equation for the reaction of calcium with water.
Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)
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What is the trend in solubility of Group 2 hydroxides?
Solubility increases down the group. Mg(OH)₂ is 'sparingly soluble', while Ba(OH)₂ is considered 'soluble'.
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What is the trend in solubility of Group 2 sulfates?
Solubility decreases down the group. MgSO₄ is very soluble, while BaSO₄ is insoluble.
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Explain the use of BaSO₄ in medicine.
It's used as a 'barium meal'. The dense, insoluble BaSO₄ is opaque to X-rays and coats the digestive tract, allowing it to be imaged. Its insolubility makes it non-toxic.
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What is the trend in thermal stability of Group 2 carbonates?
Thermal stability increases down the group. MgCO₃ decomposes at a lower temperature than BaCO₃.
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Explain why thermal stability of carbonates increases down Group 2.
Down the group, the M²⁺ cation gets larger with a lower charge density. It has less polarising power, so it distorts the electron cloud of the carbonate anion (CO₃²⁻) less. This makes the C-O bonds within the carbonate ion stronger and harder to break.
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Write the general equation for the thermal decomposition of a Group 2 nitrate.
2M(NO₃)₂(s) → 2MO(s) + 4NO₂(g) + O₂(g). Brown fumes of NO₂ are a key observation.
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How does magnesium react with steam, and how does this differ from its reaction with cold water?
With steam: Mg(s) + H₂O(g) → MgO(s) + H₂(g). It forms the oxide. With cold water, it reacts very slowly to form the hydroxide: Mg(s) + 2H₂O(l) → Mg(OH)₂(aq) + H₂(g).
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What is the chemical test for a sulfate ion?
Add dilute acid (e.g. HCl) to remove interfering ions like carbonates, then add aqueous barium chloride (BaCl₂). A white precipitate of barium sulfate (BaSO₄) confirms the presence of sulfate ions.