Group 2 - Alkali Earth Metals

Question 1

describe the trend in atomic radius going down group 2

Answer 1

increases going down group 2

Question 2

what block is group 2 in on the periodic table?

Answer 2

s

Question 3

describe and explain the trend in ionisation energy going down group 2

Answer 3

• decreases going down group 2
• extra shells added = more shielding = weaker attraction between nucleus and outer electrons
• outer e further from nucleus = weaker attraction
• less energy needed to remove outer e

Question 4

describe and explain the trend in melting points going down group 2

Answer 4

• general decrease going down group
• as go down group, size of metal ion increases but charge (+2) and number of delocalised electrons remain the same
• makes it easier to break bonds as less energy required, resulting in a lower mp
• exception for Mg due to structural difference

Question 5

what is formed when a group 2 element reacts with water?

Answer 5

a base

Question 6

describe and explain how the reactivity of group 2 elements with water differ going down the group?

Answer 6

• increases going down group
• atom gets larger so outer e further from nucleus, more shielding = weaker force of attraction between the nucleus and outer e
• easier to remove and therefore more reactive

Question 7

how does magnesium react with water?

Answer 7

• reacts slowly with cold water but more vigorously with steam
• when reacting with steam, it produces magnesium oxide (MgO) rather than magnesium hydroxide

Question 8

write an equation for the reaction of strontium, a group 2 element, with water

Answer 8

Sr_(s) + 2H₂O_(l) –> Sr(OH)_{2 (aq)} + H_{2 (g)}

Question 9

describe the solubility of group 2 elements forming hydroxides

Answer 9

• increase solubility going down the group
• magnesium = sparingly soluble
• calcium = slightly soluble
• strontium = fairly soluble
• barium = very soluble

Question 10

describe the solubility of group 2 elements forming sulfates

Answer 10

• decrease solubility going down the group
• magnesium = very soluble
• calcium = fairly soluble
• strontium = slightly soluble
• barium = sparingly soluble

Question 11

what is the general rule regarding the solubility of group 2 elements?

Answer 11

• if the anion (negative ion) has a double charge, they become less soluble going down the group
• if the anion has a single charge they become more soluble going down the group

Question 12

describe how to test for the presence of sulfates using barium chloride

Answer 12

1) add HCl to remove any carbonates (which would also form a white precipitate, giving a false result)
2) add barium chloride
if present, a white precipitate will form

Question 13

write an equation for the reaction between barium chloride and zinc sulfate

Answer 13

BaCl_{2 (aq)} + ZnSO_{4 (aq)} –> BaSO_{4 (s)} + ZnCl_{2 (aq)}

Question 14

why is barium chloride used to test for sulfates?

Answer 14

the sulfate ions displace the chloride ions to form an insoluble salt (barium sulfate)

Question 15

how can group 2 elements be used for neutralisation?

Answer 15

• Ca(OH)₂ can be used to neutralise acidic soils
• Mg(OH)₂ can be used as antacids to neutralise excess stomach acid

Question 16

write the ionic equation for neutralisation

Answer 16

H⁺ + OH^-_(aq) -> H₂O_(l)

Question 17

explain how barium can be used in medicine

Answer 17

• barium sulfate is used in “barium meals”
• used to help identify problems with the digestive tracts
• patient drinks a suspension of barium sulfate which coats soft tissues eg the stomach
• patient has an x-ray - barium sulfate will show up on the x-ray (x-ray normally doesn’t show soft tissues)
• usually barium compounds are toxic, however barium sulfate is insoluble so it can’t be absorbed into bloodstream

Question 18

explain how titanium can be extracted using magnesium. write an equation for this

Answer 18

1. Titanium ore (TiO₂) is converted to titanium(IV)chloride (TiCl₄) by heating with carbon and chlorine gas
2. Titanium(IV)chloride passed through fractional distillation column to increase purity
3. Purified TiCl₄ reduced using Mg in 1000c furnace
   - TiCl₄ + 2Mg -> Ti + 2MgCl₂

Question 19

describe the removal of sulfur dioxide from flue gases

Answer 19

• wet scrubbing can be used (alkali used to neutralised SO₂)
• calcium oxide/carbonate reacts with sulfur dioxide to remove it from factory pollutants and prevent it from being released into atmosphere
• forms calcium sulfite and water
• CaCO_3(s) + 2H₂O_(l) + SO_2(g) ->CaSO_3(s) + 2H₂O_(l) + CO_2(g)
• CaO_(s) + 2H₂O_(l) + SO_2(g) ->CaSO_3(s) + 2H₂O_(l)