Inorganic group 2

What happens to atomic radius as you go down the group?

Increases as atoms have more shells of electrons making the atom bigger- higher energy levels being filled whose orbitals are further form nucleus and as no of protons inc so does no of shielding electrons so effective nuclear charge remains constant

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What happens to first ionisation energy as you go down the group?

Decreases-no. shielding e- inc & distance of outer e- from nucleus inc. outermost e- held more weakly b/ they are successively further from nucleus in additional shells(outweighs nuclearcharge)

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What else?

. Outer e- more shielded from attraction of the nucleus by the repulsive force of inner shell electrons (repulsing electrons)

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What happens to melting point as you go down the group?

Decreases

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Be-Mg? Mg-Ca? Ca-Ba?

dec, inc, dec

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What does a metals mp depend on? how is it affected by AR? Size? what happens to Distance?

Strength of metallic bond. Inc AR so weaker attraction between nucleus and delocalised electrons. Mp Weakens as atom size inc and down group distance b/w +ve ion and delocalised e-s inc so electrostatic attractive forces b/w +ve ion and e- weaken

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Why is the mp of Mg lower than expected?

Due to variation in how its atoms pack in the metallic crystal - lattice weaker?

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Why is Ti extracted?

Useful as abundant low density and corrosion resistant-strong light alloys in planes

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Why can't you use C to extract? Why not Electrolysis? so what is it extracted with?

TiC (titanium carbide) formed, has to be pure. By a reaction with a more reactive metal eg Mg or Na

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What are the first steps ? why?

TiO2 (s) in converted into TiCl4(l) at 900c as can then be purified by fractional distillation as molecular ( liquid) at room temp rather than TiO2 ionic (s) at room temp

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Eqn for the conversion

TiO2+2Cl2+2C=TiCl4 + 2CO

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How is TiCl4 purified?

By fractional distillation in an Ar atmosphere

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How is it then extracted by magnesium?

In an Ar atmosphere at 500c- TiCl4+2Mg=Ti+MgCl2

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Why is Ti expensive?

Cost of magnesium, Batch process-slow process more labour and energy lost when reactor cools after stopping. Ar and the need to remove moisture as Ti susceptible to hydrolysis and high temp in both steps

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What does this mean for Ti?

make is expensive even though relatively abundant metal therefore used for a limited amount even though has useful properties

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What happens to the reactivity of group 2 metals as you go down the group?

Increases

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What do group 2 metals do in oxygen?

Burn

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What does Mg burn with? Eqn?

Bright white flame. 2Mg+O2=2MgO

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What is MgO?

White solid with high mp due to its ionic bonding

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What does Mg also do without a flame?

React with Oxygen slowly eg Mg ribbon has thin layer of MgO that has to be cleaned off by emery paper before doing reactions with Mg ribbon

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Why?

If testing for reaction rates with Mg and acid, an un-cleaned Mg ribbon would give a false result because both the Mg and MgO would react but at different rates. Mg + 2HCl=MgCl2 + H2 / MgO + 2HCl=MgCl2 + H2O false result

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Flame colour for Mg, Ca, Sr and Ba?

white, brick red, red/crimson, pale green/yellow

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What does Mg burn in to produce MgO and hydrogen?

Steam- bright white flame

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EQN?

Mg(s)+H2O(g)=MgO(s)+H2(g)

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What will Mg also react with giving a different magnesium hydroxide product?

Warm water- Mg+2H2O=Mg(OH)2 + H2

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What is the difference?

Much slower reaction than with steam and there is no flame

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What will the other group 2 metals react with? to form what?

Cold water with increasing vigour. hydroxides

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eqn?

metal+2H2O(l)=metal(OH)2(aq)+H2(g)

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What does the hydroxide produced do?

make water alkaline if soluble in water

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What is seen as you go down the group?

fizzing more vigorous, metal dissolving faster, solution heating up more,

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What is formed with Calcium?

White precipitate appears- less precipitate down the group

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What happens to group 2 hydroxides down the group? what does this mean?

Become more soluble down the group. PH inc as more dissolves so greater conc of OH- ions in the solution.

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What do all group 2 hydroxides appear as when not soluble?

White precipitate

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What is magnesium hydroxide?

Insoluble in water

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eqn?

Mg2+(aq) +2OH-(aq)=Mg(OH)2(s)

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What will a suspension of magnesium hydroxide in water appear as?

Slightly alkaline ph9 so some hydroxide ions must therefore have been produced by a v slight dissolving

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What is Mg(OH)2 used in? why?

Medicine in suspension as milk of magnesia to neutralise excess acid in stomach acid and to treat constipation-safe to use as so weakly alkaline and preferred over Caco3 as won't produce CO2

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EQN?

Mg(OH)2+HCl=MgCl2+H2O

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What would Barium hydroxide easily dissolve in? What would the hydroxide ions present do?

Water. Make solution strongly alkaline Ba(OH)2(s)+aq= Ba2+(aq)+2OH-(aq)

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What is Calcium hydroxide like? What will it appear as? What is it used in? Why is it more alkaline than Mg(OH)2

Partially soluble in water. White precipitate.Used in agriculture to neutralise acidic soil. Suspension of Ca(OH)2 in water more alkaline as more soluble so more hydroxide ions present in solution

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What is an aqueous solution os Calcium hydroxide? whats it used to test for? how? eqn?

Lime water. Test for CO2. Limewater turns cloudy as white calcium carbonate precipitate is produced. Ca(OH)2(aq)+CO2(g)=CaCO3(s)+H2O(l)

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What is the other use of Calcium oxide/ Calcium carbonate?

To remove SO2 from flue gas

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Summary what happens as you go down the group to AR? I.E? M.P? Reaction with water? Hydroxide solubility? Sulphate solubility?

Inc, Dec,Dec Inc Dec, Inc, Inc, Dec

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What happens to group 2 sulphates as you go down the group?

Less soluble

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Which is least soluble?

BaSO4

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Full eqn, Ionic eqn

SrCl2(aq)+Na2SO4(aq)= 2NaCl(aq)+SrSO4(s). Sr2+(aq)+SO4(aq)2-= SrSO4(s)

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What is Barium sulphate used in? who is it given to? what does it do? why is it safe to use?

Used in medicine as 'barium meal' and given to patients who need x-rays of their intestines. Absorbs X-Rays so gut shows up on X-Ray image. Even though barium compounds are toxic it is safe to use here because of its low solubility.

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What happens when Barium metal is reacted with sulphuric acid, why? eqn?

Will only react slowly as insoluble Barium sulphate produced will cover surface of metal and act as a barrier to further attack. Ba+H2SO4=BaSO4+H2.

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what happens with metals going up group? what about with other acids like hydrochloric/nitric, why?

Same effect but to a lesser extent with metals going up group as solubilities increase. Effect doesn't happen with them as form soluble group 2 salts.

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How do you test the presence of a sulphate ion? ionic eqn?

BaCl2 solution acidified with hydrochloric acid is used as a reagent to test for sulphate ions. When added to Solu containing Sulphate ions a white precipitate of Barium sulphate forms. Ba2+(aq)+SO4(aq)2-=BaSO4(s)

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What should other anions give?

negative result which is no precipitate forming

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Why is the Hydrochloric acid needed?

To react with carbonate impurities that are often found in salts which would form a white barium carbonate precipitate and so give a false result

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Why can't you use sulphuric acid?

It contains Sulphate ions and so would give a false positive result

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eqn?

2HCl+Na2CO3=2NaCl+H2O+CO2

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When would fizzing due to CO2 be observed?

if carbonate was present

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What are spectator ions?

Ions that aren't changing state or changing oxidation number

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How are insoluble salts made? what type of reaction is this?

by mixing appropriate solution of ions so that a precipitate is formed. Precipitation reaction

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Inorganic group 2

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