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Group 2 Elements & Compounds. Trends in Chemical Properties. Reaction with Water. Reactivity increases down the group N o of energy levels increases down group Outer “s” e - further from nucleus More easily lost. Metal Hydroxides. Milk of Magnesia
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Group 2 Elements & Compounds Trends in Chemical Properties
Reaction with Water • Reactivity increases down the group • No of energy levels increases down group • Outer “s” e- further from nucleus • More easily lost
Metal Hydroxides • Milk of Magnesia • suspension of Mg(OH)2 in water taken to neutralise acid indigestion . • Very weak alkali • Excess doesn’t disturb digestion (sparingly soluble)
Metal Hydroxides • MgCl2(aq) + 2NaOH(aq)→ Mg(OH)2(s) + 2NaCl(aq) • white precipitate • BaCl2(aq) + 2NaOH(aq)→ Ba(OH)2(aq) + 2NaCl(aq) • no precipitate
Metal Sulphates • Barium Sulphate – extremely insoluble in water • BaSO4 is opaque to X rays • Suspension of BaSO4 given to patients with digestive problems • X-ray will highlight problems
Metal Sulphates • MgCl2(aq) + Na2SO4(aq) → MgSO4(aq) + 2NaCl(aq) • no precipitate • BaCl2(aq) + 2NaSO4(aq)→ BaSO4(s) + 2NaCl(aq) • white precipitate
Test for Sulphate ions • Add dilute nitric acid (this prevents the formation of unwanted precipitates) • Add few drops of Barium nitrate Or • Add dilute hydrochloric acid (this prevents the formation of unwanted precipitates) • Add few drops of Barium chloride
Test for Sulphate ions BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq) white precipitate If sulphate ions are present in solution a white ppt of barium sulphate will form. Ba(NO3)2(aq) + 2KSO4(aq) → BaSO4(s) + 2KNO3(aq) white precipitate