group 2, the alkaline earth metals (A1 inorganic chemistry) Flashcards
explain the trend in melting point down group 2
general decrease further down group
size of metal ion increasing but charge on ion and number of delocalised electrons stays the same, meaning there is a greater distance between the positive nuclei of the metal ions and the delocalised elections, weakening the electrostatic attraction
there is a dip at magnesium that does not follow the trend, this is because magnesium forms a different crystal structure to the other metals in group 2
trends in electron configuration, atomic radius, and first ionisation energy down group 2
all group 2 metals have an electron configuration that ends in s²
atomic radius decreases down groups as more shells are added
first ionisation energy decreases down group due to increasing atomic radius and more shielding effect, weakening the attraction between nucleus and outer electrons
reaction of group 2 elements with water
group 2 metals react with water with increasing reactivity down the group to form metal hydroxides (bases)
X (s) + 2H₂O (l) → X(OH)₂ (aq) + H₂ (g)
magnesium reacts very slowly in cold water, but reacts much more vigorously with steam, burning bright white, to produce magnesium oxide (MgO)
Mg (s) + H₂O (g) → MgO (s) + H₂ (g)
solubility of group 2 compounds
generally, if the anion has a single negative charge, group 2 compounds will become more soluble as we go down the group
generally, if the anion has a double negative charge, group 2 compounds will become less soluble going down the group
sulfates (SO₄²⁻)
magnesium - very soluble
calcium - fairly soluble
strontium - slightly soluble
barium - sparingly soluble
hydroxides (OH⁻)
magnesium - sparingly soluble
calcium - slightly soluble
strontium - fairly soluble
barium - very soluble
testing for sulfates
- add hydrochloric acid (HCl) to remove any carbonates that could precipitate out and give a false result
- add barium chloride
- if the compound contains sulfate ions, a white precipitate of insoluble barium sulfate will form
Ba²⁺ (aq) + SO₄²⁻ (aq) → BaSO₄ (s)
BaCl₂ (aq) + XSO₄²⁻ (aq) → BaSO₄ (s) + XCl₂ (aq)
group 2 compounds to neutralise acids
calcium hydroxide Ca(OH)₂ (slaked lime) is sprayed onto acidic soils to neutralise them
magnesium hydroxide Mg(OH)₂ is used to neutralise excess stomach acid
ionic equation for neutralisation - H⁺ (aq) + OH⁻ (aq) → H₂O (l)
barium meals
barium sulfate is used to help identity problems in the digestive tract
a patient drinks a suspension of barium sulfate, which coats the lining of soft tissue such as the stomach, before an x-ray
x-rays are absorbed by barium sulfate so will show up on the results, whereas soft tissues would normally not show up as x-rays pass straight through
barium compounds are toxic, however since barium sulfate is insoluble it cannot be absorbed by the blood
extraction of titanium
- titanium ore (TiO₂) is converted to titanium(IV) chloride (TiCl₄) by heating with carbon and chlorine gas, we have to heat it with chlorine as we do not want the titanium to react with the carbon to form titanium carbide (TiC) which is brittle
- the titanium(IV) chloride is passed through a fractional distillation column to increase its purity
- the purified TiCl₄ is reduced to pure titanium with molten magnesium at 1000°C in an argon atmosphere, this is done so the titanium does not react with nitrogen or oxygen in the air and become brittle
TiCl₄ + 2Mg → Ti + 2MgCl₂
Ti⁴⁺ + 4e⁻ → Ti
Mg → Mg²⁺ + 2e⁻
the extraction of titanium is a relatively inefficient method as it is made by a batch process
titanium is lightweight but strong, and is commonly used in planes
removal of sulfur dioxide emissions
when we burn fossil fuels, we emit flue gases which contain the harmful pollutant sulfur dioxide
we can use calcium carbonate or calcium oxide (alkali) to neutralise sulphur dioxide in a process called wet scrubbing, where the calcium carbonate or calcium oxide is dissolved in water and sprayed on acidic sulfur dioxide gases before they are released into the environment
the product formed is calcium sulfite, which can be sold and used in the production of plasterboard
CaCO₃ (s) + H₂O (l) + SO₂ (g) → CaSO₃ (s) + 2H₂O (l) + CO₂ (g)
CaO (s) + 2H₂O (l) + SO₂ (g) → CaSO₃ (s) + 2H₂O (l)
formation of group 2 oxides
group 2 metals react with oxygen to form metal oxides
2X + O₂ → 2XO
when group 2 carbonates are heated to high temperatures, metal oxides can be formed from their decomposition
XCO₃ → XO + CO₂
