Group 2 Redox Reactions with Dilute Acids

All group 2 metals undergo redox reactions with dilute acids to form a salt and hydrogen gas.metal + acid → salt + hydrogen The reactivity increases down the group.Mg(s) + 2HCl(aq) → MgCl₂ + H₂(g)This is a single displacement redox reaction: the hydrogen ion of the acid is replaced by a metal ion. Magnesium is oxidised from 0 to +2 and hydrogen is reduced from +1 to 0. The chloride ion, Cl^-, is a spectator ion, so the ionic equation is:Mg(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂(g)You see fizzing (effervescence) as hydrogen is given off, and the metal dissolves. All Group 2 metals react with dilute acids, so they are all more reactive than hydrogen.The reactivity increases down the group because the sum of the first two ionisation energies decreases. The atomic radius and the shielding increase, so the outer electrons are held less strongly and are lost more easily. Group 2 elements therefore become stronger reducing agents down the group.With dilute sulfuric acid, calcium, strontium and barium form sulfates that are only slightly soluble or insoluble. The sulfate can coat the metal and slow the reaction down.