3.2.2 Alkaline Earth Metals Flashcards
Describe the use of magnesium in the extraction of titanium from titanium ore
Titanium ore (TiO2) is converted into TiCl4 by heating with carbon in chlorine gas. TiCl4 is purified by fractional distillation and reduced in a 1000°C furnace
TiO2 + 2Cl2 + C —> TiCl4 + CO2
TiCl4(g) + 2Mg(l) —> Ti(s) + 2MgCl2(l)
Explain how Mg(OH)2 is sparingly soluble
Very low solubility. The bond between magnesium and hydroxyl radical stronger than the bond that would be form between hydroxyl radical and hydrogen so it won’t dissolve in water. It thermally decomposes when reacting with steam
Describe the use of Mg(OH)2 in medicine
Used as an antacid as its alkaline and can neutralise acids
Describe the use of Ca(OH)2 in agriculture
It’s alkaline so can neutralise acidic soil
Describe the use of CaO or CaCO3 to remove SO2 from flue gases
They react with sulfur dioxide to remove from factory pollutants and prevent it from being released to atmosphere.
CaO + 2H2O + SO2 —> CaSO3 + 2H2O
CaCO3 + H2O + SO2 —> CaSO3 + H2O + CO2
Explain how BaSO4 is insoluble
Barium sulfate has a high lattice energy which is significantly greater than its hydration energy
Describe the use of acidified BaCl2 solution to test for sulfate ions + explain why it’s acidified
If you add dilute HCl and then BaCl2 solution to a compound containing sulfate ions, a white precipitate (X sulfate) will form.
The acid reacts with any carbonate ions present. This removes them, so stopping them giving a false positive result
Describe the use of BaSO4 in medicine
Barium meals- insoluble so isn’t absorbed into bloodstream. X rays pass through soft tissue in digestive system. Barium sulfate is opaque to X-rays so the tissues will show up
Describe the reactions of group 2 elements with water
Increase in reactivity
Be- reacts with steam at high temperature to give white beryllium oxide and hydrogen
Mg- burns in steam to produce white magnesium oxide and hydrogen/ very slow with water to form Mg(OH)2 and hydrogen - sparingly soluble
Ca, Sr, Ba- reacts with cold water (increasing vigour) to give metal hydroxides and hydrogen
Ca(OH)2- slightly soluble
Sr(OH)2 + Ba(OH)2- soluble
Ba- no reaction due to resistant oxide layer
Trend in sulphate solubility down group 2
Decrease
MgSO4 soluble
BaSO4 insoluble
Trend in melting point down group 2
Decrease
Sea of delocalised electrons further from positive charge of nucleus
Weaker metallic bonds/forces of attraction
Less energy to break
What are flue gases
Gases produced by power stations which are harmful to the environment
Why is using BaSO4 safe in medicine
Ba^2+ is toxic
Barium sulphate is insoluble
How can BaCl2 be used to test for sulphate ions
Add to sample with HCl
White ppt will form if sulphate ions present
Ba^2+ + SO4^2- —> BaSO4
Trend in hydroxide solubility down group 2
Increases
MgSO4 most soluble
BaSO4 least
