[3.2.2] Group 2, the Alkaline Earth Metals Flashcards
Describe and explain the trend in atomic radius from Mg-Ba.
- Atomic radius increases down the group.
- As one goes down the group, the atoms have more shells of electrons making the atom bigger.
Describe and explain the trend in melting point from Mg-Ba.
- Melting point decreases down the group.
- The metallic bonding weakens as the atomic size increases.
- The distance between the positive ions and delocalized electrons increases.
- Therefore, the electrostatic attractive forces between the positive ions and delocalized electrons weaken.
Describe and explain the trend in the first ionisation energy from Mg-Ba.
- The outermost electrons are held more weakly because they are successively further from the nucleus in additional shells.
- In addition, the outer shell electrons become more shielded from the attraction of the nucleus by the repulsive force of inner shell electrons.
Describe the trend in reactivity in group 2.
The reactivity of group 2 metals increases down the group.
Describe the reaction of magnesium in oxygen.
What equation represents this reaction, what would you observe?
- Magnesium reacts in oxygen to produce magnesium oxide.
- 2 Mg (s) + O₂ (g) -> 2 MgO (s)
- The Mg would burn with a bright white flame.
- The MgO appears as a white powder.
Describe the reaction of magnesium in steam.
What equation represents this reaction, what would you observe?
- Magnesium reacts in steam to produce magnesium oxide and hydrogen.
- Mg (s) + H₂O (g) -> MgO (s) + H₂ (g)
- The Mg would burn with a bright white flame.
- The MgO appears as a white powder.
Describe the reaction of magnesium in warm water.
What equation represents this reaction, what would you observe?
- Magnesium will react with warm water giving magnesium hydroxide as a product.
- Mg + 2 H₂O (I) -> Mg(OH)₂ (aq) + H₂ (g)
- Slow reaction and no flame unlike when Mg reacts with steam.
Describe the reaction of calcium in cold water.
What equation represents this reaction, what would you observe?
- Calcium will react with cold water giving calcium hydroxide as a product.
- Ca + 2 H₂O (I) -> Ca(OH)₂ (aq) + H₂ (g)
- Fizzing, metal dissolving, solution heating up & white precipitate appearing.
Describe the reaction of strontium in cold water.
What equation represents this reaction, what would you observe?
- Strontium will react with cold water giving strontium hydroxide as a product.
- Sr + 2 H₂O (I) -> Sr(OH)₂ (aq) + H₂ (g)
- **Fizzing, metal dissolving & solution heating up.
Describe the reaction of barium in cold water.
What equation represents this reaction, what would you observe?
- Barium will react with cold water giving barium hydroxide as a product.
- Ba + 2 H₂O (I) -> Ba(OH)₂ (aq) + H₂ (g)
- **Fizzing, metal dissolving & solution heating up.
What are the relative solubilities of the hydroxides of elements Mg-Ba in water?
_ GROUP II HYDROXIDES BECOME **MORE SOLUBLE ** DOWN THE GROUP_
- Magnesium hydroxide, Mg(OH)₂ = insoluble - appears as white precipitate.
- Calcium hydroxide, Ca(OH)₂ = partially soluble - appears as white precipitate.
- Strontium hydroxide, Sr(OH)₂ = soluble.
- Barium hydroxide, Ba(OH)₂ = soluble.
Write the ionic equations for the formation of group 2 hydroxide precipitates.
MAGNESIUM HYDROXIDE
- Mg²⁺ (aq) + 2 OH⁻ (aq) -> Mg(OH)₂ (s).
CALCIUM HYDROXIDE
- Ca²⁺ (aq) + 2 OH⁻ (aq) -> Ca(OH)₂ (s).
(Because Mg & Ca hydroxides are partially insoluble/insoluble, they form precipitates which you can write ionic equations for)
What are the relative solubilities of the sulfates of elements Mg-Ba in water?
_ GROUP II HYDROXIDES BECOME **LESS SOLUBLE ** DOWN THE GROUP_
- Magnesium sulfate, MgSO₄ = soluble.
- Calcium sulfate, CaSO₄ = partially soluble.
- Strontium sulfate, SrSO₄ = insoluble.
- Barium sulfate, BaSO₄ = insoluble.
Write the ionic equations for the formation of group 2 sulfate precipitates.
CALCIUM SULFATE
- Ca²⁺ (aq) + SO₄²⁻ (aq) -> CaSO₄ (s)
STRONTIUM SULFATE
- Sr²⁺ (aq) + SO₄²⁻ (aq) -> SrSO₄ (s)
BARIUM SULFATE
- Ba²⁺ (aq) + SO₄²⁻ (aq) -> BaSO₄ (s)
(Because Ca, Sr & Ba sulfates are partially insoluble/insoluble, they form precipitates which you can write ionic equations for)
Describe the properties and uses of titanium.
Describe how we use magnesium to extract titanium from TiCl₄, include equations.
Explain why titanium is expensive.
PROPERTIES & USES OF TITANIUM
- Abundant, low density and corrosion resistant.
- Used for making strong, light alloys for use in aircraft.
TITANIUM IS EXTRACTED BY REACTION WITH A MORE REACTIVE METAL
-
TiO₂ (solid) is converted to TiCl₄ (liquid) at 900°C.
- TiO₂ is converted to TiCl₄ as it can be purified by fractional distillation, TiCl₄ being molecular (liquid at room temp.) rather than ionic like TiO₂ (solid at room temp.).
- TiO₂ + 2 Cl₂ + 2 C -> TiCl₄ + 2 CO.
- The TiCl₄ is purified by fractional distillation in an argon atmosphere.
- The Ti is extracted by Mg in an argon atmosphere at 500°C.
- TiCl₄ + 2 Mg -> Ti + 2 MgCl₂.
WHY IS THIS PROCESS EXPENSIVE?
- The expensive cost of the magnesium.
- This is a batch process which makes it expensive because the process is slower and requires more labour and the energy is lost when the reactor is cooled down after stopping.
- The process is also expensive due to the argon, and the need to remove moisture because TiCl₄ is susceptible to hydrolysis.
- High temperatures are required in both steps.
(This all makes titanium expensive even though it is a relatively abundant metal. It is only therefore used to a limited amount even though it has useful properties)
