group 2 Flashcards
(32 cards)
how does atomic radius change down group 2?
increases down the group
as you go down group, number of electron shells increases so shielding increases
nuclear attraction therefore decreases making the atom bigger
how do melting points change down group 2?
decreases
the metallic bonding weakens as atomic size increases
distance between positive ions and delocalised electrons increases
therefore electrostatic forces of attraction between positive ions and sea of delocalised electrons becomes weaker
how does first ionisation energy change down group 2?
decreases
the outermost electrons are held more weakly because shielding increases so nuclear attraction decreases
so easier to remove one mole of electrons in gaseous state
what is the general equation for the reaction of all metals with water?
(M represents metal)
M(s) + 2H20(l) —–> M(OH)2 (aq) + H2 (g)
produces an alkaline which is soluble in water
which group 2 metal doesn’t react with water?
Be
What is the equation for Mg reacting with steam?
Mg(s) + H2O(g) ——-> MgO(s) + H2(g)
produces a base which is insoluble in water
what is the observation for when Mg reacts with cold water?
very very slow reaction and a bubble may be seen
Mg is sparingly soluble
what observations can be seen when Mg reacts with steam?
white light/ glow and white solid( powder) formed
what is the observation for when Ca reacts with water?
effervescence
white solid of slightly soluble Ca(OH)2
Some Ca(OH)2 dissolves to give alkaline solution
what is the observation for when Sr reacts with water?
effervescence
less white solid Sr(OH)2 is more soluble
what is the observation for when Ba reacts with water?
effervescence
no white solid because Ba(OH)2 is soluble
what are group 2 hydroxides classified as?
almost all bases and react with acids
Ba is alkali as it is completely soluble and Sr because it is nearly as soluble as Ba
how does the solubility of the group 2 hydroxides change down the group and what does this mean for the resultant pH solution?
sol. increases down group and so does pH due to OH- ions
how do we test the relative solubility of group 2 hydroxides?
adding aqueous sodium hydroxide to solutions of the group 2 ions and observing precipitates formed
what would be observes for Magnesium and Barium hydroxide when reacted with sodium hydroxide?
Mg(OH)2 is sparingly soluble so a thick white precipitate will form
Ba(OH)2 is much more soluble so a very thin white precipitate would form which would go colourless if you add more NaOH
what is magnesium hydroxide used for?
in medicine for an indigestion remedy called milk of magnesia- used to neutralise stomach acid
what is calcium hydroxide used for?
used in agriculture to neutralise the acidic soil
also aqueous solution is called lime water and can be used to test for carbon dioxide
how does the solubility of group 2 sulfates change down the group?
decreases
calcium sulfate is sparingly soluble and barium sulfate is insoluble
how do we test solubility of group 2 sulfates?
add sulfuric acid or sodium sulfate to solutions containing group 2 ions and observe precipitates formed
MgSO4 is soluble hence no ppt would be seen
BaSO4 is insoluble so a thick white ppt would be seen
e.g. SrCL2 + H2SO4 —–> SrSO4 + 2H2O
what can we use to help us test for sulfate ions?
barium salts
describe the method of using barium salts to test for sulfates?
to 1cm3 of the unknown sample
add 1cm3 of HCl (to remove other ions such as carbonates)
add 1cm3 of BaCl2 solution
BaCl2 +MgSO4 ——> MgCl2 +BaSO4
what is the observation for sulfate ions using barium salts?
thick white precipitate
what is the use of barium sulfate in medicine?
used in a barium meal used for patients who need X-rays of their intestines
BaSO4 is good at absorbing X-rays which allows gut to be seen on X-rays
barium ions are toxic, how come we can still use the barium meal?
barium sulfate is insoluble so the barium ions are not absorbed into the blood
