Group 2 and testing for aqueous cations and anions Flashcards
Describe and explain the trend in atom radius down group 2
Increases
Extra electron shells get added
Describe and explain the trend in ionisation energies down group 2
Each subsequent element has an extra electron shell than the previous
Meaning there is more shielding so the outer electrons is further away from the nucleus leading to a lower attraction
This makes it easier for an electron to be removed from the outer shell
Trend in boiling points down group 2
Decreases down the group
As the atoms get bigger there is a weaker attraction between the delocalised electrons and positive nuclei.
Takes less energy to break the bonds.
Magnesium doesn’t evenly fit the trend due to a difference in arrangement of metallic ions.
Group 2 reactions with water?
Form a metal hydroxide and hydrogen
When group 2 metals react they are oxidised and form +2 ions
They react more readily down the group due to decreasing ionisation energies
Describe the relative solubilities of the group 2 metals with both hydroxides and sulfates?
Group 2 elements in compound with OH- increase in solubility down group 2
- Starting with magnesium hydroxide which is described as sparingly soluble
-Barium hydroxide dissolves to produce a strongly alkaline solution
Group 2 elements in compound with SO42- decrease in solubility down group 2
How can the property of barium solubility be used to test for sulfates?
As barium sulfate is insoluble when barium chloride reacts with a solution containing sulfate ions eg. FeSO4 a white ppt of barium sulfate forms.
Solution needs to be acidified with HCl to remove any sulfites or carbonates.
This indicates the presence of sulfate ions
Uses of magnesium hydroxide and calcium hydroxide
Magnesium hydroxide is used as an antacid - neutralises excess stomach acid - therefore is an effective component of an indigestion tablet.
Calcium hydroxide is used in agriculture to neutralise soils
Use of barium sulfate
Barium Meal in xrays
Is opaque to xrays and coats the tissues meaning they show up on the scans
What is the use of magnesium?
Magnesium is used as a reducing agent in the process of extracting titanium from its ore
The titanium ore is converted to titanium chloride by heating it with carbon in a steam of chlorine gas
The magnesium reduces the titanium chloride.
TiCl4 + 2Mg -> 2MgCl2 + Ti
Roles of calcium oxide and calcium carbonate?
Flue gas desulferisation
Powdered CaO or CaCO3 is mixed with water to form a slurry.
Its then sprayed onto the flue gases.
The sulfer dioxide reacts with the alkaline slurry and produces a solid waste product eg. calcium sulfite
How to test for metal ions using flame tests?
Flame test - Dip platinum loop in HCl
Calcium = orange/red
Lithium = red
Potassium = lilac
Sodium = yellow
Barium = green
Cu2+ = green/blue
How to test for ammonium ions?
Add NaOH solution and head
Damp red litmus paper will turn blue
Magnesium reaction with water
Product and observations?
Magnesium Hydroxide + Hydrogen gas
Bright white flame and a white powder
