3.2.2 Group 2, the alkaline earth metals

Question 1

Describe the structure of alkaline metals

Answer 1

All elements in grp 2 have 2 electrons in the outermost s sub level and are metals.
As you go down the group, an extra shell is added.
They have a Giant metallic structure

Question 2

Describe the trend in atomic radius for group 2

Answer 2

As you go down the group, the atomic radius increases because the atoms have more shells of electrons

Question 3

Describe the trend in ionisation energy for grp 2

Answer 3

As you go down the group, ionisation energy decreases because atomic radius is increased as electron shells increase and shielding effect increases so there is a weaker attraction between the nucleus and outer shell electron

Question 4

Describe the trend in the m.p. of grp 2

Answer 4

As you go down the group, melting points decrease because cations get larger, so there is a weaker electrostatic attraction between cations and delocalised electrons so less energy needed to overcome the attraction

Question 5

Describe the trend in the reactivity for grp2

Answer 5

Reactivity of grp 2 metals increases going down the group as cation radius increases as there are a greater number of electron shells. So attraction between cation and delocalised electrons becomes weaker, so outer shell electrons are easier to remove

Question 6

Describe the trend in reducing power of grp 2

Answer 6

Reducing power of grp2 increases down the group as cation radius increases as electron shells increase so attraction between cation and delocalised electrons becomes weaker so outer shell electrons are easier to remove

Question 7

What is the general equation for grp 2 metals reacting with oxygen?

Answer 7

2M + O2 -> 2MO

Question 8

Describe what happens when grp 2 metals react with oxygen

Answer 8

Metals lose electrons in chemical reactions and act as good reducing agents. They can react with other elements to form an ionic compound

Question 9

What is the general equation for grp2 reacting with water?

Answer 9

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

Question 10

What is the ionic equation for grp 2 reacting with water?

Answer 10

M(s) + 2H2O(l) -> M2+(aq) + 2OH-(aq) + H2(g)

Question 11

What is the oxidation reaction of grp2 reacting with water?

Answer 11

M -> M2+ + 2e-
(metal oxidised, it is the reducing agent)

Question 12

What is the reduction reaction of grp2 reacting with water?

Answer 12

2H2O + 2e- -> 2OH- + H2
(water reduced, it is the oxidising agent)

Question 13

What happens when magnesium reacts with steam?

Answer 13

Doesn’t really react with water itself.??? questionable
Mg(s) + H2O(g) -> MgO(s) + H2(g)
Observation: white solid and bright light

Question 14

What happens when calcium reacts with water?

Answer 14

Water should be in excess
Ca(s) + 2H2O(l) -> Ca(OH)2(aq) + H2(g)
Observation: Colourless solution and effervescence

Question 15

What do grp 2 compounds and solutions look like?

Answer 15

Compounds (solids) = white
Solutions = colourless

Question 16

What is the trend of the solubilities of grp 2 hydroxides?

Answer 16

Solubilities increase going down group2
- Mg(OH)2 is sparingly soluble. Ca(OH)2 is slightly soluble and the others are soluble.
They also get more alkaline going down

Question 17

What is the trend of the solubilities of grp 2 sulphates?

Answer 17

Solubilities decrease going down group 2

Question 18

What is the use of CaCO3/ CaO?

Answer 18

In agriculture to neutralise acidic soil

Question 19

What is the use of Mg(OH)2?

Answer 19

As an antacid to neutralise stomach acid/ indigestion relief

Question 20

What is the use of barium sulfate?

Answer 20

Use barium meal/ barium swallow for X-ray because BaSO4 is insoluble

Question 22

How can flue gasses be removed?

Answer 22

By passing them through a slurry of calcium oxide or calcium carbonate (wet scrubbing). As sulfur dioxide is an acidic gas and CaO/CaCO3 are basic, sulfur dioxide can react with wet mixture of calcium oxide/ calcium carbonate in an acid base reaction

Question 23

What is the reaction taking place in flue gas desulfurisation with CaO?

Answer 23

CaO(s) + SO2(g) -> CaSO3(s)
2CaSO3(s) + O2(g) -> 2CaSO4(s)

Question 24

What is the reaction taking place in flue gas desulfurisation with CaCO3?

Answer 24

CaCO3(s) +SO2(g) ->CaSO3(s)+CO2(g)
2CaSO3(s) + O2(g) -> 2CaSO4(s)

Question 25

What is titanium useful for?

Answer 25

It’s a very strong, low density metal, which is resistant to corrosion, even in extreme conditions. It is used in the aerospace industry

Question 26

What can magnesium be used for?

Answer 26

To extract titanium from it’s ore (rutile)

Question 27

How can titanium be extracted from its ore?

Answer 27

TiO2 (s) is converted to TiCl4(l) by heating with carbon and chlorine gas.
TiO2 + 2Cl2 + 2C -> TiCl4 + 2CO
Titanium chloride produced is then purified by fractional distillation in an argon atmosphere.
Purified TiCl4 is reduced using more reactive magnesium in a furnace at 1000 degrees C.
TiCl4 + 2Mg -> Ti + 2MgCl2
Mg behaves as a reducing agent (donates electrons to TI)

Question 28

Why can’t titanium be extracted using carbon?

Answer 28

Carbon is a cheap reducing agent, however titanium forms a carbide TiC, which is an impurity and can ruin the metal

Question 29

How can you test for sulfate ions?

Answer 29

Reagent: BaCl2 solution acidified with hydrochloric acid
Observation: White precipitate forms BaSO4 (s)
Chemical equation: BaCl2 (aq) + Na2SO4(aq) -> 2NaCl(aq) + BaSO4(s)
Ionic equation: Ba2+(aq)+ SO4 2-(aq) -> BaSO4(s)

Question 30

Why is an acid used in testing for sulfate ions?

Answer 30

HCl is needed to remove carbonate impurities (often found in salts with could form a white barium carbonate precipitate so give a false result)