Group 2 Flashcards
Density
Group 2 metals are harder and have higher density than group 1 metals bc group 2 ions are smaller than group 1 ions so they pack more closely together.
Reactivity of group 2 metals
They are all reactive metals with similar chemical reactions bc they have the same number of electrons in the outer shell.
Appearance of group 2 compounds
-Ionic
-White crystalline solids at room temp
Trends down group 2
Atomic radius increases - more shells, more shielding, weaker attraction between nucleus and outer e-
1st IE decreases - larger atomic radius, more shielding, weaker attraction between nucleus and outer e-
Melting point decreases - ionic radius increases, distance between nucleus and delocalised e- increases, weaker attraction between nucleus and outer e-
Reaction of Mg with cold water
-Very slow reaction
-Few bubbles form on surface of Mg
Mg + 2H2O —> Mg(OH)2 + H2
Reaction of Mg with steam
-Bright white light
-White solid forms (Mgo)
Mg(s) + H2O(g) —> MgO(s) + H2(g)
Reaction of other group 2 metals with cold water
-fizzing
-Solid group 2 metal disappears
-Some white solid is formed (less solid forms as you go down the group)
With Barium:
-Fizzing
-Solid Ba disappears to give colourless solution
-No white solid forms
Reactivity of group 2 elements as you go down the group
Reactivity increases as you go down because
-atomic radius increases
-more shielding
-weaker attraction between nucleus and outer e-
-so e- are lost more easily
How to use Mg in the extraction of titanium from TiCl4
1) Titanium oxide (TiO2) reacted with Cl2 and C to form Titanium(IV) chloride, TiCl4. Chlorine is reduced.
2) TiCl4 then reduced with 2Mg to produce Ti and 2MgCl. Mg = reducing agent.
Group 2 hydroxides - M(OH)2
Solubility of group 2 hydroxides in water increases down the group.
Use of group 2 hydroxides
Mg(OH)2 used in medicine - in indigestion tablets to neutralise excess stomach acid (HCl)
Ca(OH)2 used in agriculture - neutralises acids in soil (HNO3 and H2SO4)
Group 2 Sulfates - MSO4
Solubility of group 2 Sulfates decreases down the group
Identifying Mg2+ ions in solutions
Done by adding aqueous NaOH to a solution of the group 2 compound being tested and observing the precipitates formed.
MCl2(aq) + 2NaOH(aq) —> M(OH)2 + 2NaCl(aq)
-Mg sparingly soluble as the pH of solution is slightly alkaline so a small amt of OH ions dissolved. Hence thick white precipitate would be seen, ionic eqn:
Mg2+(aq) + 2(OH-)(aq) —> Mg(OH)2(s)
-Ba(OH)2 much more soluble so precipitate does not form and a colourless solution would be seen (no ionic eqn)
Identifying Ba2+ ions in solutions
Done by adding H2SO4 or aq Na2SO4 to a solution of the group 2 compound and observing the precipitates formed.
MCl2(aq) + H2SO4 —> MSO4 + 2HCl(aq)
-BaSO4 is insoluble so a thick white precipitate would be seen, ionic eqn:
Ba2+(aq) + (SO4)2-(aq) —> BaSO4(S)
-MgSO4 is soluble so a precipitate does not form and a colourless solution would be seen (no ionic eqn)
Uses of barium salts (BaCl2, Ba(NO3) )
Can be used to test for (SO4)2- ions.
Method:
-Get 1cm^3 of solution to be tested
-Add an acid (always aq) to remove (CO3)2- ions that would cause a false positive (BaCO3 = white solid)
-Add aq Barium salt (BaCl2 aq)
-If white solid is seen: solution tested contains (SO4)2-
Method is same for Magnesium salts but don’t need to add an acid, replace the Ba with Mg and replace the SO4 with OH- bc Mg salts can be used to test for OH- ions.
Use of BaSO4 in medicine
Used as a contrast agent in x-rays.
-Ba ions are toxic but this technique is harmless bc the BaSO4 is insoluble so Ba ions are not absorbed into the blood.
Uses of Ca compounds
CaO or CaCO3 can be used to remove SO2 from flue gas
-SO2 = acidic gas
-CaO/CaCO3 = bases
Equations:
SO2 + CaO —> CaSO3
SO2 +CaCO3 —> CaSO3 + CO2
