group 2

Question 1

describe the redox reactions of group 2 metals

Answer 1

each metal atom is oxidised, forming a 2+ ion
the group 2 metal acts as a reducing agent, as it causes another species to gain electrons

Question 2

describe and give the equation for the redox reactions of group 2 metals (M) with oxygen

Answer 2

group 2 metals react with oxygen to form a metal oxide
2M + O2 ——> 2MO (metal oxide, made of M2+ and O2- ions)

Question 3

describe the redox reactions of group 2 metals (M) and water

Answer 3

group 2 metals react with water to form an alkaline hydroxide
reactivity increases down the group
M + 2H2O ——> M(OH)2 + H2

Question 4

describe the redox reactions of group 2 metals with dilute acids

Answer 4

metal + acid ——> salt + hydrogen
reactivity increases down the group

Question 5

describe/explain the trend in reactivity for group 2 metals

Answer 5

the reactivity increases down the group

group 2 elements react by losing 2 electrons, requiring the input of 2 ionisation energies
down the group, the ionisation energies decrease due to increased atomic radius and increased shielding (so less nuclear attraction to outer electrons), making the metals more reactive

Question 6

describe what happens when water is added to group 2 oxides

Answer 6

the oxides react with water, releasing hydroxide ions and forming alkaline solutions of the metal hydroxides

Question 7

give the equation for the reaction of calcium oxide and water

Answer 7

CaO (s) + H2O(l) ——> Ca2+(aq) + 2OH-(aq)

Question 8

what happens when more water is added to group 2 hydroxides? give the equation

Answer 8

a solid precipitate will form from the metal and hydroxide ions, as the group 2 hydroxides are only slightly soluble in water
Ca2+(aq) + 2OH-(aq) ——> Ca(OH)2 (s)

Question 9

describe the trend in solubility/alkalinity of group 2 hydroxides

Answer 9

the solubility of the hydroxides in water increases down the group, so the resulting solutions contain more OH- ions and are therefore more alkaline (pH increases)

Question 10

explain the approximate pH of Mg(OH)2 compared to Ba(OH)2 when dissolved in water

Answer 10

Mg(OH)2 is only slightly soluble in water, so has a low OH- concentration and a pH of ~10

Ba(OH)2 is much more soluble in water, so has a higher OH- concentration and a pH of ~13

Question 11

give 2 applications of using group 2 compounds as bases

Answer 11

• agriculture
• medicine

Question 12

describe the uses of group 2 compounds in agriculture and give the equation

Answer 12

calcium hydroxide is added to fields as lime to increase the pH of acidic soils, neutralising acids in the soil to form water
Ca(OH)2 (s) + H+ (aq) —-> Ca2+ (aq) + 2H2O (l)

Question 13

describe the uses of group 2 compounds in medicine and give the equations

Answer 13

group 2 bases, e.g. calcium carbonates and magnesium hydroxide, are often used as antacids for treating acid indigestion

Mg(OH)2 (s) + 2HCl (aq) ——-> MgCl2(aq) + 2H2O (l)

CaCO3 (s) + 2HCl (aq) —–> CaCl2 (aq) + H2O (l) + CO2(g)