Group 2, the alkaline earth metals Flashcards
Describe how the atomic radius changes down group 2.
Atomic radius increases down the group. As one goes down the group, the atoms have more
shells of electrons making the atom bigger.
Describe how the melting point changes down group 2.
Melting points decrease 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 the
delocalized electrons weaken.
Describe how the 1st ionisation energy changes down group 2.
Increased shells and increased shielding therefore less electrostatic between the nucleus and outer electron so it’s easier to lose.
Reactivity in Group 2.
Reactivity of group 2 metals increases down the group
The general equation for when G2 metals react with water.
Metal + Water ——–> Metal hydroxide + Hydrogen
State the equation and observations for the reaction between Mg and steam.
Mg (s) + H2O (g) —–> MgO (s) + H2 (g)
The Mg would burn with a bright white flame.
State the equation and observations for the reaction between Mg and warm water.
Mg + 2 H2O ——> Mg(OH)2 + H2
No reaction with cold water
White solid formed, fizzing
State the equation and observations for the reaction between Ca and cold water.
Ca + 2 H2O (l) ——> Ca(OH)2(aq) + H2(g)
Fizzing, white solid forming and slightly soluble.
General observations of reactions down group 2.
Fizzing, (more vigorous down group)
The metal dissolving, (faster down group)
The solution heating up (more down group)
With calcium, a white precipitate appearing
(less precipitate forms down the group with
other metals)
State the equation and observations for the reaction between Sr and cold water.
Sr + 2 H2O (l) ——> Sr(OH)2(aq) + H2(g)
Fizzing, colourless solution formed
State the equation and observations for the reaction between Ba and cold water.
Ba + 2 H2O (l) ——-> Ba(OH)2(aq) + H2(g)
Fizzing, colourless solution formed.
Steps in extracting titanium:
- TiO2 (solid) is converted to TiCl4 (liquid) at 900C.
- The TiCl4 is purified by fractional distillation in an argon atmosphere.
- The Ti is extracted by Mg in an argon atmosphere at 500C.
- TiO2 is converted to TiCl4 as it can be purified by fractional distillation, TiCl4 being molecular
(liquid at room temperature) rather than ionic like TiO2 (solid at room temperature).
Why can’t Titanium be extracted with Carbon?
Titanium cannot be extracted with carbon because titanium carbide (TiC) is formed rather
than titanium.
Titanium cannot be extracted by electrolysis as it has to be very pure.
Why is titanium expensive?
- The expensive cost of the Mg
- This is a batch process which makes it expensive because the process is slower (having to fill up and empty reactors takes time) 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 required in both steps
Uses of titanium.
Titanium is a very useful metal because it is abundant, has a low density and is corrosion resistant – it is used for making strong, light alloys for use in aircraft.
Solubility of Group 2 Hydroxides
Group II hydroxides become more soluble down the group. All Group II hydroxides when not
soluble appear as white precipitates
Solubility of Magnesium Hydroxide
Magnesium hydroxide is classed as insoluble in water.
A suspension of magnesium hydroxide in water will appear slightly alkaline (pH 9) so some
hydroxide ions must therefore have been produced by a very slight dissolving.
Uses of magnesium hydroxide.
Magnesium hydroxide is used in medicine (in suspension as milk of magnesia) to neutralise
excess acid in the stomach and to treat constipation.
Solubility of Calcium hydroxide
Calcium hydroxide is classed as partially soluble in water and will appear as a white precipitate.
Uses of Calcium hydroxide.
It is used in agriculture to neutralise acidic soils
Group 2 Sulphate Solubility
Group II sulphates become less soluble down the group. BaSO4 is the least soluble.
Use of Barium sulfate.
BaSO4 is used in medicine as a ‘Barium meal’ given to patients who need x-rays of their
intestines. The barium absorbs the X-rays and so the gut shows up on the x-ray image.
This is because barium is insoluble so its not absorbed into the blood
Test for Sulphate Ions
- Add HCl first – This reacts and removes any sulphites or carbonates that may also give a
white precipitate. - Add BaCl2 solution: If sulphates are present, a white precipitate of BaSO4 will form