Chemistry - 3.2.2: Group 2, the Alkaline Earth Metals

Alkaline earth metals

The elements in group 2

Why are group 2 metals called alkaline earth metals?

Their oxides and hydroxides are alkaline

Are alkaline earth metals more or less reactive than group 1 metals?

They are less reactive

How many electrons do group 2 metals have on their outer s-orbital?

2

What happens to atomic radii as you go down group 2?

Atomic radii increases - each element has an extra filled main level of electrons compared to the one above it

What happens to melting point as you go down group 2?

Melting point decreases: larger atomic radii so metallic bonds become weaker
Magnesium has the lowest melting point - exception

What happens to ionisation energy as you go down group 2?

Ionisation energy decreases: larger atomic radii and more shielding, so weaker attraction between outer electrons and nucleus

What happens to group 2 metals in all their reactions?

They are oxidised - oxidation state changes from 0 to +2

Symbol equation for reaction of Mg with cold water

Mg (s) + H2O (l) -> Mg(OH)2 (aq) + H2 (g)

What forms when group 2 metals react with cold water?

Metal hydroxide + hydrogen gas

Symbol equation for reaction of Mg with steam

Mg (s) + H2O (g) -> MgO (s) + H2 (g)

What happens to solubility of the group 2 hydroxides as you go down group 2?

Become more soluble:
- Mg(OH)2: almost insoluble, not sold as solution
- Ca(OH)2: sparing soluble, solution = limewater
- Sr(OH)2: more soluble
- Ba(OH)2: dissolves to form a strongly alkaline solution

What forms when you dissolve group 2 metals in water?

A white precipitate

What happens to the solubility of the sulfates as you go down group 2?

Become less soluble as you go down the group

How is magnesium used to extract titanium from TiCl4?

- Titanium can't be extracted with carbon like other metals as titanium carbide is brittle
- So, titanium ore is first reacted with chlorine and carbon to form TiCl4 and CO
- TiCl4 is then reacted with magnesium and is reduced to titanium (magnesium chloride also forms)

How is Mg(OH)2 used in medicine?

Milk of Magnesia: used to treat indigestion, heartburn and wind by neutralising excess stomach acid

How is Ca(OH)2 used in agriculture?

Slaked lime: used to treat acidic soil, make it more alkaline so optimum conditions for plants

How is CaO / CaCO3 used to remove SO2 from flue gases?

- Flue gases: gases released from chimneys and exhausts of factories that burn fossil fuels
- Flue gases contain SO2: air pollutant that causes acid rain (+ other damage to environment and organisms)
- Slurry made using powdered CaO / CaCO3 and water, sprayed onto flue gases: reacts with SO2, CaO and CaCO3 both alkaline, so can remove acidic SO2

How is acidified BaCl2 solution used to test for sulfate ions?

- BaCl2 solution first acidified with HNO3 acid or HCl acid
- BaSO4 is very insoluble, so if SO4 2- ions are present, a white precipitate of BaSO4 forms (Cl2 is displaced by SO4)

Why must the BaCl2 solution be acidified in order to test for sulfate ions? (2)

- Removes any carbonate ions in the sample as they would react with barium to form barium carbonate, another white precipitate - both carbonates and sulfates produce this!
- By adding HCl, this reacts with any CO3 2- ions, so only precipitate formed is from So4 2-

How is BaSO4 used in medicine?

- Ingested as 'barium meal':
- Barium atoms are heavy, X-rays cannot pass through it
- So BaSO4 can be used to outline the gut on an X-ray (stomach + oesophagus)
- Barium sulfate is very insoluble so the test is safe even though barium compounds are toxic

Symbol equation for magnesium reacting with titanium (IV) chloride

2Mg + TiCl4 -> 2MgCl2 + Ti

When adding equal molar amounts of two group 2 metals, how can you test which solution would have the highest pH? (3)

- Metals react with water, form metal hydroxides
- Lower in group 2, more soluble the hydroxide is
- So group 2 metal that is lower would produce more OH- ions when in solution, resulting in a higher pH (test with pH metre)

How do you test which group 2 metal is more soluble? (3)

- Add same number of moles of each metal and water to a test tube
- Test for pH of each solution using a pH metre
- If more soluble, there is a higher concentration of OH- ions, so would have a higher pH

Reaction of CaCO3 to remove SO2 (include state symbols)

CaCO3 (s) + SO2 (g) -> CaSO3 (s) + CO2 (g)

Reaction of CaO to remove SO2 (include state symbols)

CaO (s) + SO2 (g) -> CaSO3 (s)

Which group 2 metal has the lowest melting point?

Magnesium

What might you observe when magnesium reacts with steam? (2)

Bright, white light OR a white powder