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)

Describe reactivity with water descending group 2 of group 2 elements

increases

Describe reactivity with water/steam of Be

Does not react with water or steam

Describe reactivity with water/steam of Mg

does not react readily with water

reacts with steam to from metal oxide and hydrogen

Equation for Mg and water and state pH. state observations

Mg(s) + H₂O(l) → Mg(OH)₂ + H_2(g)

ph = 9

Mg(OH)₂ is sparingly soluble so low conc of OH- ions

Obs - white solid and bright white light

Equation for Ca and water and state pH.

Ca(s) + 2H₂O(l) → Ca(OH)₂ (s) + H_2(g)

pH = 10

Equation for Ba/Sr and water and state pH. State observations

Ba(s) + 2H₂O(l) → Ba(OH)₂ (aq) + H_2(g)

pH = 14

Sr(s) + 2H₂O(l) → Sr(OH)₂ (aq) + H_2(g)

Describe reactivity with water/steam of Ba/Sr

react vigourosly with cold water

what are Ba(OH)₂ and Sr(OH)₂?

Colourless solutions

Use of magnesium hydroxide

relieve indigestion

‘milk of magnesia’

use of calcium hydroxide

neutralise acidic soil

Use of barium sulphate and side effects

‘barium meal’ - good at absorbing X-rays

Barium ions are very toxic however barium sulphate is insoluble in water

Why is titanium useful? Used for what

abundant

low density

corrosion resistant

Aircraft

Where does titanium come from

rutile ore contains titanium oxide.

Why can titanium not be extracted with carbon?

Titanium carbide (TiC) forms not titanium

How is titanium extracted? What does rutile make under what conditions?

reaction with more reactive metal

TiO₂ converted to TiCl₄ using carbon in a stream of chlorine gas at 900 c

TiO₂ converted to TiCl₄ using carbon in a stream of chlorine gas at 900 c

Write an equation for this reaction and state the reducing agent

TiO₂ + C +2Cl₂ → TiCl₄ + CO₂

Carbon

How is TiCl₄ reduced?

Write an equation and state which element is the reducing and oxidising agent

Na or Mg in a stream of argon gas at 600c

TiCl₄ + 2Mg→ 2 MgCl₂ + Ti

Mg - oxidised → reducing agent

Ti - reduced → oxidising agent

Why is this reaction done in atmosphere of argon?

inert atmosphere

No argon means Titanium reacts with oxygen nd nitrogen in the air at high temperatures