In fact, 1 liter of water dissolves about 2 mg of barium sulfate at room temperature. The ready formation of a precipitate indicates that barium sulfate is quite insoluble. Barium sulfate exists as a white precipitate in solution.Notice that a solution, and not a precipitate, is formed, implying that magnesium sulfate is soluble. A familiar reaction is that between magnesium and dilute sulfuric acid, producing hydrogen gas and a colorless solution of magnesium sulfate.For example, beryllium (the first element in Group 2) has an atomic radius of 112 pm, whereas calcium (further down the group) has. The top metal cations in the group are smaller in size than those at the bottom. As two electrons are lost from their valence shells, all Group 2 metals form 2+ ions. Two common examples illustrate this trend: Trends in Thermal Stability of Group 2 Metals. Solubility figures for magnesium sulfate and calcium sulfate also vary depending on whether the salt is hydrated or not, but the variations are less dramatic. The Nuffield Data Book quotes anyhydrous beryllium sulfate, BeSO 4, as insoluble, whereas the hydrated form, BeSO 4.4H 2O is soluble, with a solubility of about 39 g of BeSO 4 per 100 g of water at room temperature. This simple trend is true provided hydrated beryllium sulfate is considered, but not anhydrous beryllium sulfate. The sulfates become less soluble down the group.Barium hydroxide is soluble enough to produce a solution with a concentration around 0.1 mol dm -3 at room temperature.A liter of pure water will dissolve about 1 gram of calcium hydroxide at room temperature. Calcium hydroxide solution is referred to as "lime water".This is because some magnesium hydroxide has dissolved. This indicates that there are more hydroxide ions in solution than there were in the original water. However, if it is shaken in water and filtered, the solution is slightly basic. Magnesium hydroxide appears to be insoluble in water.The following examples illustrate this trend: Since the atomic radii increase down the group it makes sense that the coordination numbers also increases because the larger the metal ion the more room there is for water molecules to coordinate to it. The larger the lattice energy the more energy it takes to break the lattice apart into metal and hydroxide ions. This trend can be explained by the decrease in the lattice energy of the hydroxide salt and by the increase in the coordination number of the metal ion as you go down the column. Group II metal hydroxides become more soluble in water as you go down the column.
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