3.2.2 Group 2, the alkaline earth metals Flashcards
Describe the structure of alkaline metals
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
Describe the trend in atomic radius for group 2
As you go down the group, the atomic radius increases because the atoms have more shells of electrons
Describe the trend in ionisation energy for grp 2
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
Describe the trend in the m.p. of grp 2
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
Describe the trend in the reactivity for grp2
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
Describe the trend in reducing power of grp 2
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
What is the general equation for grp 2 metals reacting with oxygen?
2M + O2 -> 2MO
Describe what happens when grp 2 metals react with oxygen
Metals lose electrons in chemical reactions and act as good reducing agents. They can react with other elements to form an ionic compound
What is the general equation for grp2 reacting with water?
M(s) +2H2O(l) -> M(OH)2(aq) + H2(g)
What is the ionic equation for grp 2 reacting with water?
M(s) + 2H2O(l) -> M2+(aq) + 2OH-(aq) + H2(g)
What is the oxidation reaction of grp2 reacting with water?
M -> M2+ + 2e-
(metal oxidised, it is the reducing agent)
What is the reduction reaction of grp2 reacting with water?
2H2O + 2e- -> 2OH- + H2
(water reduced, it is the oxidising agent)
What happens when magnesium reacts with steam?
Doesn’t really react with water itself.??? questionable
Mg(s) + H2O(g) -> MgO(s) + H2(g)
Observation: white solid and bright light
What happens when calcium reacts with water?
Water should be in excess
Ca(s) + 2H2O(l) -> Ca(OH)2(aq) + H2(g)
Observation: Colourless solution and effervescence
What do grp 2 compounds and solutions look like?
Compounds (solids) = white
Solutions = colourless
What is the trend of the solubilities of grp 2 hydroxides?
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
What is the trend of the solubilities of grp 2 sulphates?
Solubilities decrease going down group 2
What is the use of CaCO3/ CaO?
In agriculture to neutralise acidic soil
What is the use of Mg(OH)2?
As an antacid to neutralise stomach acid/ indigestion relief
What is the use of barium sulfate?
Use barium meal/ barium swallow for X-ray because BaSO4 is insoluble
How can flue gasses be removed?
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
What is the reaction taking place in flue gas desulfurisation with CaO?
CaO(s) + SO2(g) -> CaSO3(s)
2CaSO3(s) + O2(g) -> 2CaSO4(s)
What is the reaction taking place in flue gas desulfurisation with CaCO3?
CaCO3(s) +SO2(g) ->CaSO3(s)+CO2(g)
2CaSO3(s) + O2(g) -> 2CaSO4(s)
What is titanium useful for?
It’s a very strong, low density metal, which is resistant to corrosion, even in extreme conditions. It is used in the aerospace industry
What can magnesium be used for?
To extract titanium from it’s ore (rutile)
How can titanium be extracted from its ore?
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)
Why can’t titanium be extracted using carbon?
Carbon is a cheap reducing agent, however titanium forms a carbide TiC, which is an impurity and can ruin the metal
How can you test for sulfate ions?
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)
Why is an acid used in testing for sulfate ions?
HCl is needed to remove carbonate impurities (often found in salts with could form a white barium carbonate precipitate so give a false result)
