Group 2 Flashcards
What are the elements in Group 2?
The alkaline earth metals
What are the most common types of reaction of Group 2?
Redox reactions
What type of agent is a Group 2 element?
Reducing
What do Group 2 elements react with to form a metal oxide?
Oxygen
2Mg(s) + O2(s) -> 2MgO (s)
Mg is oxidised
O is reduced
How do Group 2 elements react with water?
G2 metal + water = alkaline hydroxide + hydrogen gas
Sr (s) + 2H2O -> Sr(OH)2 (aq) + H2 (g)
How do Group 2 elements react with dilute acids?
Metal + acid -> salt + hydrogen
Mg (s) + 2HCl (aq) + MgCl2 (aq) + H2(g)
What does reactivity do down Group 2?
Increases. The ionisation energies decrease down the group due to larger atomic radius and higher electron shielding. Therefore, electrons are lost easier so reactivity increases
How do Group 2 oxides react in water?
The react with water, releasing hydroxide ions and forming alkaline solutions of the metal hydroxide. They are only slightly soluble in water
CaO (s) + H2O (l) -> Ca 2+ (aq) + 2OH - (aq)
How are Group 2 hydroxides formed?
Ca 2+ (aq) + 2 OH - (aq) -> Ca(OH) 2 (s)
What does the solubility of Group 2 hydroxides do down the group?
It increases down the group, so the resulting solutions contain more OH - ions are are more alkaline
How can you show the trend in Group 2 hydroxides increasing solubility?
1) Ass a spatula of each Group 2 oxide to water in a test tube
2) Shake the mixture. On this scale, there is insufficient water to dissolve all of the metal hydroxide that forms. You will have a saturated solution of each metal hydroxide with some white solid undissolved at the bottom of the test-tube
3) Measure the pH of each solution. The alkalinity will be seen to increase down the group
How are Group 2 compounds used in agriculture?
Calcium hydroxide, Ca(OH)2, is added to fields as lime by farmers to increase the pH of acidic soils. The calcium hydroxide neutralises acid in the soil, forming neutral water:
Ca(OH)2 (s) + 2H + (aq) -> Ca 2+ (aq) + 2 H2O (l)
How are Group 2 compounds used in medicine?
Group 2 bases are often used as antacids for treating acid indigestion. Many indigestion tablets use magnesium and calcium carbonates as the main ingredients.
The acid in your stomach is mainly hydrochloric acid and the equations below show the neutralisation reactions that take place with Mg(OH) 2 and CaCO3
Mg(OH)2 (s) + 2HCl (aq) -> MgCl2 (aq) + 2H2O (l)
CaCO3 (s) + 2HCl (aq) -> CaCl2 (aq) + H2O (l) + CO2 (g)
