Group 2 (alkaline earth metals)

Question 1

what is the trend in atomic radius as you go down group 2 and why

Answer 1

Increases

• number of shells increases = shielding increases
• less electrostatic attraction between V electrons and nucleus
• Radius increases

Question 2

what is the trend in 1st ionisation energy as you go down group 2 and why

Answer 2

Decreases

• shielding increases
• less electrostatic attraction between V electrons and nucleus
• less energy needed to remove electron
• 1st ionisation energy decreases

Question 3

what happens when group 2 metal react with water

Answer 3

they lose 2 electrons and form a metal hydroxide

Question 3

what is the trend in melting point as you go down group 2 and why

Answer 3

Decreases

• size of the metal ion increases
• weaker electrostatic attraction between positive metal ion nucleus and negative delocalised electron
• less energy needed to break the metallic bonds
• melting point decreases

Question 4

whats the general equation for the reaction of a group 2 metal with water

Answer 4

M + 2H₂O → M(OH)₂ + H₂

Question 4

which metals form a white precipitate when reacted with water

Answer 4

Mg and Ca

• Both hydroxides are insoluble

Question 5

how to test for barium ions

Answer 5

• add sulfuric acid (H₂SO₄) or sodium sulfate (Na₂SO₄)
• barium sulfate will form which is a white precipitate due to it being insoluble

Question 5

why does the ph increases as the solubility of the hydroxides increases

Answer 5

there are more hydroxides ions in the solution which are alkali

Question 5

which metals do NOT form a white precipitate when reacted with water

Answer 5

Sr and Ba

• Both hydroxides are soluble

Question 6

What is the trend in solubility of group 2 metal hydroxides?

Answer 6

as you go down the group the solubility increases

-Mg(OH)₂ → Ba(OH)₂ = Least to most soluble

Question 7

describe a test for hydroxide ions

Answer 7

• add magnesium chloride solution to the solution containing hydroxide ions and a white precipitate should form
• the white precipitate is magnesium hydroxide

Question 7

what is the use of BaCl₂

Answer 7

to test for sulfate ions in solutions

• Ba²⁺ + SO₄²⁻ → BaSO₄

Question 8

what do you do to a solution before testing it for sulfate ions and why

Answer 8

acidify it with HCl or HNO₃

• do this to remove any carbonate ions that would interfere with the reaction and form a false precipitate (BaCO₃)

Question 8

test for magnesium ions

Answer 8

• add sodium hydroxide solution to the solution containing magnesium ions and a white precipitate should form
• the white precipitate is magnesium hydroxide

Question 8

what is the trend in solubility of metal sulphates as you go down group 2

Answer 8

as you go down group 2 the solubility of the metal sulphates decreases

Question 8

which metal sulphate forms a white precipitate and why

Answer 8

BaSO₄

• its insoluble

Question 9

what is the use of Ca(OH)₂

Answer 9

• neutralises acidic soils
• H⁺ + OH⁻ → H₂O

Question 10

what is the use of Mg(OH)₂

Answer 10

• neutralises excess stomach acid
• H⁺ + OH⁻ → H₂O

Question 11

what is the use of CaO and CaCO₃

Answer 11

• flue gas desulfurisation ( neutralises SO₂)
• CaO + SO₂ → CaSO₃

Question 11

what is the use of BaSO₄ and why is it safe

Answer 11

• CT Scans or X-rays
• lines the digestive track with BaSO₄ to make it visible to xray
• BaSO₄ is insoluble and therefore cannot dissolve into blood

Question 12

what is the use of Mg and recall the equations

Answer 12

• used in the extraction of titanium from its ore

( first step uses chlorine and coke to turn titanium oxide into titanium chloride)

• TiO₂ + 2Cl₂ + 2C → TiCl₄ + 2CO

(second step uses Mg as a reducing agent to turn titanium chloride into Titanium)

• TiCl₄ + 2Mg → 2MgCl₂ + Ti