Why does reactivity increase as we go down group 2?
- down group 2 atomic radii increases
- due to more filled energy levels
- so outer electron is futher away from the nucleus
why does ionisation energy decrease as we go down group 2?
- due to greater atomic radii
- there is greater shielding
- therefore the outer electron is attracted less strongly so less energy is required to remove an electron
why does the melting point generally decrease as we go down group 2?
- due to increase in ionic radii
- so decrease in charge/size ratio of the ion
- so weaker metallic bonding
- so less energy required to break the metallic bonds
reactions of group 2 with water
when group 2 elements react with water they form what ions?
They’re oxidised from..? to..?
M2+ ions , oxidised from 0 -> +2
describe solubility with group 2 elements and hydroxide ions?
solubility increases as you go down group 2 when reacted with OH- ions
group 2 metals + cold water –> makes?
metal hydroxide and hydrogen
describe what happens in the reaction between magnesium and cold water?
what happens when the rest of group 2 elements react with cold water?
- Mg reacts very slowly to form magnesium hydroxide and hydrogen
Mg (s) + H2O (l) —-> Mg(OH)2 (aq) + H2 (g) - they react more vigorously with cold water
group 2 metal + steam —> makes?
metal oxide and hydrogen
describe the reaction between magnesium and steam.
what observations can be made from this reaction?
- reacts to form magnesium oxide and hydrogen
Mg (s) + H2O (g) —> MgO (s) + H2 (g) - glows a bright orange, white solid MgO formed
describe the reaction between calcium and cold water?
why is a cloudy white mixture formed?
- reacts to form calcium hydroxide and hydrogen
- because ca(OH)2 is sparingly soluble in water
what happens when strontium and barium react with cold water.
why is a colourless solution formed?
- react tor form their metal hydroxide which is a colourless solution and hydrogen
- barium hydroxide and strontium hydroxide is soluble in water
the more soluble the hydroxide the…?
why is this?
the stronger the alkali, as there is a higher content of hydroxide (OH-) ions
uses of metal hydroxides
what is Mg(OH)2 used as?
- an indigestion cure as its a weak alkali so neutralises excess stomach acid. safe to use as it’s not corrosive or toxic
- also used as a laxative
what is Ca(OH) used for?
- used by farmers in agriculture to add to soils to increase pH, neutralise acidic soils
- = limewater used to test for co2
2 word equation to show magnesium hydroxide neutralising HCL
- Mg(OH)2 (s) + 2HCL (l) —-> MgCl2 (aq) + 2H2O (l)
- Mg(OH)2 + 2H+ (aq) —> Mg2+ (aq) + 2H2O (l)
group 2 sulphates
describe solubility of group 2 sulphates down the group?
solubility decreases so Mg is the most soluble and Barium is insoluble in water (because it’s a solid)
most barium compounds are..? but..?
toxic but BaSO4 is not toxic as its’s insoluble so passes straight out of the body
how can we test for sulphate ions?
using acidified barium chloride (BaCl2) solution
if sulphate ions are present what will the solution form..?
why does it form a white precipitate?
will form a white precipitate of barium sulphate (BaSO4)
- because BaSO4 is insoluble
when do we need to make sure we add ACIDIFIED BaCl2?
needs to be acidified in order to remove carbonate ions from the solution. as CO3(2-) carbonate ions would interfere with the test and so form a false positive result of a white precipitate of BaCO3
draw the equation to show how carbonate ions interfere with the test and how carbonate ions are removed
- Ba 2+ (aq) + CO3(2-) (aq) —-> BaCO3 (s)
- CO3(2-) (aq) + 2H+ (aq) —–> CO2 + h20
