Final answer:
Magnesium and Calcium form strong bases when they react with water because they are alkaline earth metals which readily lose electrons and react with water to produce metal hydroxides and hydrogen gas. The high concentration of hydroxide ions (OH−) released during these reactions is indicative of strong bases.
Step-by-step explanation:
Magnesium (Mg) and Calcium (Ca) both form strong bases when they react with water. This is due to their position in the periodic table; they are part of the alkaline earth metals, which are known for their tendency to lose two electrons to form divalent metal ions. When Mg and Ca react with water, they form magnesium hydroxide (Mg(OH)2) and calcium hydroxide (Ca(OH)2), respectively. These reactions can be represented as Mg(s) + 2H2O(l) → Mg(OH)2 + H2(g) and Ca(s) + 2H2O(l) → Ca(OH)2 + H2(g). The products of these reactions are hydrogen gas and the respective metal hydroxide, indicating that these alkaline earth metals are better reducing agents than hydrogen.
While Mg(OH)2 is generally considered a weak base due to its low solubility in water, it is listed as a strong base in some contexts , which might indicate that it is a strong electrolyte and thus dissociates into a significant number of ions in its saturated solution. Strong bases like those of the heavy alkaline earth metals such as Ca(OH)2 are strong electrolytes, as they dissociate almost completely into ions, releasing a large concentration of hydroxide ions (OH−). This substantial availability of hydroxide ions is what characterizes a strong base.