3.2.2 Group 2 , The alkaline earth metals

Q: State and explain the trend of size of atoms in group 2 going down the group

increases

the number of energy levels increases

outer electrons are increasingly shielded from the nucleus so attraction decreases

State and explain the trend of ionisation energies going down the group

decreases

the outer electrons are more shielded from the nucleus as atoms get bigger/larger so a weaker forces of attraction for nucleus so easier to remover outer electron

State and explain the trend of melting points going down the group

decreases

size of positive ion increases but charge of ion stays the same as descend group

this means the electrostatic attraction between positive ion and delocalised electrons decreases

The solubility of the sulphates does what descending the group?

decreases

Describe solubility of MgSO4, CaSO4, SrSO4, BaSO4

MgSO4 - soluble

CaSO4 - sparingly soluble

SrSO4 BaSO4 - insoluble

Write an ionic equation for reaction of barium chloride and magnesium sulphate

Ba²⁺(aq) + SO₄^2- (aq) → BaSO4 (s)

What is BaSO4?

white ppt

Q: Why add HCL (aq) to solution before adding MgSO4 (aq)?

removes any other ions such as carbonate or hydroxide ions which may interfere with the test

Why use HCL and not sulphuric acid?

the sulphate ion may give false result as a white ppt will be formed upon addition to BaCL2

How does Hal remove carbonate and hydroxide ions?

2H⁺+CO₃^2- → CO₂ + H₂O

H⁺ + OH^- → H₂O

all nitrates are…

soluble

Test for BaCl

one test tube = BaCl2(aq)

two test tube = NaCl(aq)

State reagent and observations

reagent = MgSO₄(aq)

Obs 1 - white ppt

MgSO₄ + BaCl₂→ BaSO₄

Obs 2 - no visible reaction

MgSO₄ + BaCl₂→ BaSO_4(s) +MgCl₂ (aq)

Test for MgCl

one test tube = MgCl2(aq)

two test tube = MgSO₄(aq)

State reagent and observations

reagent = BaCl₂(aq)

Obs 1 - no visible reaction

MgCl₂ + BaCl₂→ MgCl₂ + BaCl₂ = colourless solution

Obs 2 - white ppt

MgSO₄ + BaCl₂→ BaSO₄(s)

Test for NaCl

one test tube = NaCL(aq)

two test tube = MgCl₂(aq)

State reagent and observations

reagent = NaOH(aq)

Obs 1 - no visible reaction

NaCl + NaOH → NaCl + NaOH

Obs 2 - white ppt

Mg²⁺(aq) + 2OH^-(aq) → Mg(OH)₂ (s)

Test for CaCl₂

one test tube = NaCl(aq)

two test tube = CaCl₂(aq)

State reagent and observations

reagent = NaOH(aq)

Obs 1 - no visible reaction

NaCl + NaOH → NaCl + NaOH

Obs 2 - white ppt

Ca²⁺(aq) + 2OH^-(aq) → Ca(OH)₂ (s)

Describe solubility of group 2 hydroxides descending the group

increase

Describe the solubility of Mg(OH)_2, Ca(OH)_2, Sr(OH)_2,Ba(OH)₂

Mg(OH)₂ - insoluble

Ca(OH)_{2 -} sparingly soluble

Sr(OH)₂ - soluble

Ba(OH)₂ - soluble

Write ionic equation of dilute sodium hydroxide and MgCl₂ forming a white ppt and identify it

Mg(OH)_{2 =} white ppt

[MgCl₂ (aq) + 2NaOH (aq) → Mg(OH)₂ (s) + 2NaCl (aq)]

[Mg²⁺ 2Cl^- 2Na⁺ 2OH^- → Mg(OH)₂ 2Na⁺ 2Cl^-]

Mg²⁺ (aq) + 2OH^- (aq) → Mg(OH)₂ (s)