Group 2, The Alkaline Earth Metals Flashcards
What compounds can group two metals form
All Group 2 metals can form ionic compounds in which they donate these two outermost electrons (so they act as reducing agents) to become an ion with +2 charge (so they themselves become oxidised)
What happens to group 2 reactivity further down the group
the metals become more reactive
What is first ionisation energy
The first ionisation energy is the energy needed to remove the first outer electron of an atom
What is second ionisation energy
The second ionisation energy is the energy needed to remove the second outer electron of an atom
Why does ionisation energy decrease as we go down the group
Though the nuclear charge increases going down the group (because there are more protons), factors such as an increased shielding effect and a larger distance between the outermost electrons and nucleus outweigh the attraction of the higher nuclear charge
This ionisation energy trend is shown by looking at reactions of the Group 2 metals:
With dilute hydrochloric acid: bubbles of hydrogen gas are given off much faster indicating that the reactions become more vigorous
With oxygen: the metals get more reactive with oxygen down the group (Ba is so reactive, that it must be stored in oil to prevent it from reacting with oxygen in air)
What happens to the melting point as yoyu move down the group
The melting point of the elements decreases going down the group as the outer electrons get further away from the nucleus
This means that the attraction between the nucleus and the bonding electrons decreases causing a decrease in melting point
What happens to the density as we move down the group
the density of the alkali earth metals drops and then increases
Density is also affected by the packing structure of the metals, not just the atomic radius
Group 2 hydroxides as we move down the group
the solutions formed from the reaction of group 2 oxides with water become more alkaline
When the oxides are dissolved in water, what following ionic reaction takes place
O2- (aq) + H2O (l) → 2OH- (aq)
What makes the solution more alkaline
The higher the concentration of OH- ions formed, the more alkaline the solution
The alkalinity of the solution formed can therefore be explained by the solubility of the Group 2 hydroxides
What equation shows the hydroxides dissolve in water
X(OH)2 (aq) → X2+ (aq) + 2OH- (aq)
What happens to group 2 hydroxide solubility as it moves down the group?
Going down the group, the solubility of these hydroxides increases
This means that the concentration of OH- ions increases, increasing the pH of the solution
oing down the group, the alkalinity of the solution formed increases when Group 2 oxides react with water
How are group two hydroxides formed
When the metal oxides react with water, a group 2 hydroxide is formed
What happens to the solubility of the sulfates going down the group?
the solubility of the sulfates decreases
Uses of calcium - limestone
this is impure calcium carbonate
Uses of calcium - quick lime
this is calcium oxide, formed by the thermal decomposition of calcium carbonate
Uses of calcium - slaked lime
this is calcium hydroxide formed when water is added to quicklime
How is calcium used in agriculture
agriculture to raise the pH of the soil
Over time, the soil becomes more acidic while the optimum pH for many crops to grow is at around 6-6.5
The compounds are all bases and react with the acids in the soil and raise the pH of the soil
Why is Calcium carbonate more commonly used in agricultural lime
it is cheaper and safer to handle
However, due to calcium carbonate being largely insoluble, it acts more slowly than calcium hydroxide
What are calcium compounds used to remove
Calcium compounds are also used to remove sulfur dioxide from flue gases in a process known as sulfur scrubbing
How is barium sulfate used in medicine
A barium meal or barium swallow containing BaSO4 is given to a patient who needs an X-ray on their intestines
Barium absorbs X-rays which means the gut shows up white on the image
Why can barium be used in medicine even though it is toxic?
Barium sulfate is insoluble so is not absorbed into the blood
The barium meal or swallow is only a small amount for the patient to ingest
What is magnesium hydroxide used for
to neutralise excess acid in the stomach and treat constipation. This is because magnesium hydroxide, Mg(OH)2, is partially soluble in water and is used in suspension (known as ‘milk of magnesia’)
What is the equasion of nuetralising acid in stomach with magnesium hydroxide
Mg(OH)2 (s) + 2HCl (aq) → MgCl2 (aq) + 2H2O (l)
Why is magnesium hydroxide safe?
magnesium hydroxide is only partially soluble making the solution only slightly alkaline (pH ≅ 10) due to the low OH- concentration
How is magnesium used for the extraction of titanium from the ore TiO2
TiO2 is heated in a stream of chlorine, in the presence of coke, to produce TiCl4
Then titanium is extracted from its chloride by reduction with magnesium (sodium can also be used)
titanium is extracted from its chloride by reduction with magnesium equasion
TiCl4 (g) + 2Mg (l) → Ti (s) + 2MgCl2 (l)
TiO2 is heated in a stream of chlorine equasion
TiO2 (s) + 2C (s) + 2Cl2 (g) → TiCl4 (g) + 2CO (g)
Mg - Reaction with oxygen
Burns easily
Bright white light
Ca - Reaction with oxygen
Difficult to ignite
Red flame
Sr - Reaction with oxygen
Difficult to ignite
Red flame
Ba - Reaction with oxygen
Difficult to ignite
Green flame
Mg - Reaction with water
Vigorous reaction with steam, no reaction with water
Ca - Reaction with water
Reacts moderately, forms a hydroxide
Sr - Reaction with water
Reacts rapidly, forms a hydroxide
Ba - reaction with water
Reacts rapidly, forms a hydroxide
Mg - Reaction with dilute HCl
Reacts vigorously
Ca - dilute hcl
Reacts vigorously
Sr - Reacts with dulte HCl
Reacts vigorously
Ba - Reactions with dilute Hcl
Reacts vigorously
Mg - Reaction with dilute H2SO4
Reacts vigorously
Ca - Reaction with dilute H2SO4
Reaction slowed by the formation of a sparingly soluble sulfate layer on the metal, stopping hydrogen bubbles from rising
Sr - Reaction with dilute H2SO4
Reaction is quickly stopped by the formation of an insoluble sulfate layer on the metal
Ba - Reaction with dilute H2SO4
Reaction is quickly stopped by the formation of an insoluble sulfate layer on the metal
The reaction of group 2 metals with oxygen follows the following general equation:
2M (s) + O2 (g) → 2MO (s)
Where M is any metal in group 2
Remember than Sr and Ba also form a peroxide, MO2
reaction of all metals with water follows the following general equation:
M (s) + 2H2O (l) → M(OH)2 (s) + H2 (g)
Be which does not react with water
Magnesium reacting with cold water
Mg (s) + 2H2O (l) → Mg(OH)2 (aq) + H2 (g)
The solution formed is weakly alkaline (pH 9-10) as magnesium hydroxide is only slightly soluble
magnesium is heated in steam
when magnesium is heated in steam, it reacts vigorously with steam to make magnesium oxide and hydrogen gas:
Mg (s) + H2O (g) → MgO (s) + H2 (g)
What do Group 2 metals react with dilute acids to form
colourless solutions of metal salts
What happens when some of Group 2 metals react with sulfuric acid rather than hydrochloric,
an insoluble sulfate forms
The reaction of the metals with dilute HCl follows the following general equation
M (s) + 2HCl (aq) → MCl2 (aq) + H2 (g)
The reaction of the metals with dilute H2SO4 follows the following general equation
M (s) + H2SO4 (aq) → MSO4 (aq) + H2 (g)
Remember that SrSO4 and BaSO4 are insoluble
Reactions of group 2 oxides with water
All group 2 oxides are basic, except for BeO which is amphoteric (it can act both as an acid and base)
Group 2 oxides react water to form alkaline solutions which get more alkaline going down the group
Mg - Reaction with water
MgO (s) + H2O (l) → Mg(OH)2 (s)
MgO is only slightly soluble in water, therefore a weakly alkaline solution (pH 10.0) is formed
CaO - Reaction with water
CaO (s) + H2O (l) → Ca(OH)2 (s)
A vigorous reaction which releases a lot of energy, causing some of the water to boil off as the solid lump seems to expand and open (pH 11.0)
What is calcium hydroxide also known as -
lime water
Group 2 oxides reacting with sulfuric acid.
Group 2 sulfates form
The insoluble sulfates form at the surface of the oxide, which means that the solid oxide beneath it can’t react with the acid
This can be prevented to an extent by using the oxide in powder form and stirring, in which case neutralisation can take place
Solubility in group 2 carbonates
All (except for BeCO3) are insoluble in water
All g will form soluble chloride salts, water and carbon dioxide gas when reacted with dilute hydrochloric acid
The carbonates of Ca, Sr and Ba form as an insoluble sulfate layer on their solid carbonates which stops any further reaction after the initial bubbling (effervescence) of carbon dioxide gas is seen
Group 2 Carbonates reacting with Dilute Acids word equasions.
carbonate + dilute hydrochloric acid → chloride + water + carbon dioxide
carbonate + dilute sulfuric acid → sulfate + water + carbon dioxide
