3.2.2 - group 2

why does atomic radius increase down the group

atoms have more shells of electrons

order of elements down grp 2

Be, Mg, Ca, Sr, Ba

trend of melting points down the group and why

• decreases

• as atomic size increases, metallic bonding weakens

• because distance btw positive ions and delocalized e-s increases

• so force of attraction btw them weakens

trend in 1st ionization energy down the group and why

• Decreases down the group

• Bc distance between nucleus and outer electrons successively increases

• Also increased shielding of nucelus by inner shells of e-s

• So there is a weaker force of attraction between the nucleus and outer e-

• So outermost e- = requires less energy to remove

Trend of reactivity down group 2

Increases

REACTIONS OF GROUP 2 METALS WITH OXYGEN - what do they all do in the presence of oxygen

Burn in it

What does Mg burn with

Give an equation for this

What is the product of this rxn (colour and state)

A bright white flame

2Mg + O2 —→ 2MgO

White solid, has a high m.p.

IDK IF YOU NEED THIS BUT

Can Mg react slowly with oxygen without a flame

Equation for this

what will the magnesium ribbon have a thin layer of on it

Yes

2Mg + O2 —→ 2MgO (same as before)

MgO - formed by the rxn w/ oxygen in the air

SAME IDK IF YOU NEED THIS

WHEN TESTING FOR RXN RATES WITH Mg AND ACID

• what will give a false resukt

• why

• give 2 equations to show this

• an uncleaned Mg

• both the the Mg and MgO would react but at diff rates

• 1. Mg + 2HCl —→ MgCl2 + H2

• 2. MgO + 2HCl —→ MgCl2 + H2O

what does Mg react in steam to produce

what does the Mg burn with

equation for this

magnesium oxide and hydrogen

a bright white flame

Mg (s) + H2O (g) —→ MgO (s) + H2 (g) REMEMBER THE RIGHT STATE SYMBOL !!!

what temp of WATER does Mg react with

warm water

what does it react in water to porduce

give an equation for this

is this rxn faster or slower than the steam rxn

is there a flame

magneisum hydroxide

Mg + 2 H2O —→ Mg(OH)2 + H2

slower

no

what temp of water will the other grp 2 metals react w/

they react w/ increasing vigour down the group to form… (type of product)

give all equations for this

cold water

hydroxides

Ca + 2 H2O (l) —→ Ca(OH)2 (aq) + H2 (g)

Sr + 2 H2O (l) —→ Sr(OH)2 (aq) + H2 (g)

Ba + 2 H2O (l) —→ Ba(OH)2 (aq) + H2 (g)

format for equation of grp 2 metals (except Mg) reacting with cold water

metal + 2H2O (l) —→ metal hydroxide (aq) + hydrogen (g)

the hydroxides produced make the water a___________ (if they are soluble in water)

alkaline

observations for this rxn

• fizzing, (more vigorous down group)

• the metal dissolving, (faster down group)

• the solution heating up (more down group)

• with Ca, a white ppt appearing (less precipitate forms down group with other metals)

why is titanium a useful metal

it can be used for making strong, light alloys in…

• abundant

• has a low density

• corrosion resistant

• aircraft

1. what is titanium extracted from?

2. why cant it be exttracted with carbon

3. why can’t it be extracted by electrolysis

1. titanium oxide

2. titanium carbide (TiC) it is formed rather than titanium

3. it has to be very pure

instead, its extracted by a rxn with ____________

why

magnesium

because Ti it is a highly reactive metal that forms brittle impurities (titanium carbide) if reduced with carbon. Magnesium, being more reactive than carbon, serves as a stronger, more efficient reducing agent to remove chlorine from titanium(IV) chloride

steps in extracting titanium:

1.t___________ o_________ (TiO2) is converted to t___________ c_________ (TiCl4) (liquid) at 900 degrees. c________ m___________ is also produced.

2. The TiCl4 is purified by f___________ d_____________ in an a______ atmosphere.

3. The Ti is extracted by m___________ in an argon atmosphere at 500 degrees. m____________ c__________ is also produced.

1. TiO2 (solid) is converted to TiCl4 (liquid) at 900 degrees. carbon monoxide is also produced

2. The TiCl4 is purified by fractional distillation in an argon atmosphere

3. The Ti is extracted by Mg in an argon atmosphere at 500 degrees C. magnesium chloride is also produced.

equation for step 1

equation for step 3

TiO2 + 2Cl2 + 2C —→ TiCl4 + 2CO

TiCl4 + 2Mg —→ Ti + 2 MgCl2

why is TiO2 converted to TiCl4

• it can be purified by fractional distillation as TiCl4 is molecular (which means its liquid at room temp)

  rather than ionic like TiO2 (solid at room temp)

why is titanium expensive (even though it is a relatively abundant metal)

1. The expensive cost of the Mg

2. High temps required in both steps

3. This = batch process. makes it expensive bc the process = slower (having to fill up and empty reactors takes time). It also requires more labour + energy is lost when the reactor is cooled down after stopping

4. The process = expensive due to the argon, and the need to remove moisture (because TiCl4 is susceptible to hydrolysis)

trend in solubility of grp 2 hydroxides down the grp

• become more soluble

when grp 2 hydroxides are not soluble, what do they appear as

white ppts

magnesium hydroxide is classed as s__________ s___________ in water

what does this mean

Simplest Ionic Equation for formation of Mg(OH)2 (s)?

sparingly soluble

a (solute) that dissolves only slightly in a solvent (e.g. water), often leaving most of the solid undissolved

Mg2+ (aq) + 2OH-(aq) —→ Mg(OH)2 (s)

how do we know the magneisum hydroxide slightly dissolved

A suspension of magnesium hydroxide in water will appear slightly alkaline (pH 9)

so some hydroxide ions must therefore have been produced by a very slight dissolving

NOTE: as Group 2 hydroxides become more soluble (e.g., from to ), they release more OH- ions

use of Mg(OH)2 in medicine

equation for how this works

used in milk of magnesia / indigestion tablets to reduce stomach acid (HCl)

Mg(OH)2 + 2HCl —→ MgCl2 + 2H2O

solubility of calcium hydroxide

what will it appear as

will a suspension of calcium hydroxide appear more or less alkaline than magnesium hydroxide? why?

slightly soluble

a white ppt

• more alkaline (pH 11) cause its more soluble

• so more OH- ions present in solution

what is an aqueous solution of Ca(OH)2 called

what can it test for

why does limewater turn cloudy

equation for this

lime water

CO2

white calcium carbonate is produced

Ca(OH)2 (aq) + CO2 (g) —→ CaCO3 (s) + H2O(l)

use of Ca(OH)2 in agriculture

found in lime to neutralise acidic soils

solubility of Ba(OH)2

its solubility makes it strongly alkaline. why?

easily dissolves in water

lots of OH- ions present

Ba(OH)2 (S) —→ Ba2+ (aq) + 2OH-(aq)

solubility of grp 2 sulfates down the grp

less soluble

grp 2 hydroxides = more soluble down the grp

grp 2 sulfates = less soluble down the grp

what sulfate is insoluble

BaSO4

how to write equations for formation of the ppts

Full equation : SrCl2(aq) + Na2SO4 (aq) —→ 2NaCl (aq) + SrSO4 (s)

Ionic equation: Sr2+ (aq) + SO4 2-(aq) —→ SrSO4 (s).

the use of toxic BaSO4 in medicine?

why can it be used despite its toxicity?

used in barium meals to show up the intestines during x-rays. the barium absorbs the x-rays so the gut shows up during the x-ray

its insoluble, so it passes through the gut + not absorbed into the blood

rxn of barium metal with sulfuric acid: fast or slow? why?

equation for this

slow

bc the insoluble barium sulfate produced will cover the surface of the metal and act as a barrier to any further attack

Ba + H2SO4 —→ BaSO4 + H2

as you go UP grp 2 and solubility of sulfates increases, this same effect will happen to a l________ extent

why does this same effect not happen with other acids like hydrochloric or nitric acid

lesser extent

they form soluble grp 2 salts

reagent used to test for presence of sulfate ions

positive test result (contains sulfate ions)

simplest ionic eq. for this

BaCl2 solution acidified with HCl

white ppt forms (this is barium sulfate)

Ba2+ (aq) + SO4 2-(aq) —→ BaSO4 (s)

what is the HCl needed for

why cant we use H2SO4

to react with carbonate impurities that are often found in salts. these would form a white barium carbonate ppt and so give a false positive result

contains sulfate ions and so would give a false positive result.

what two things (?) can be used to remove sulphur dioxide from flue gases in power station?

why is this done

• calcium oxide

• calcium carbonate

to prevent it escaping into the atmosphere

environmental problem caused by sulphur dioxide

acid rain

what does sulphur dioxide react with to form sulfuric (VI) acid

give an equation for this

water and oxygen

SO2 + H2O + 0.5O2 —→ H2SO4

what does calcium oxide react with sulphur dioxide to form

give an equation for this

what type of reaction is this

calcium sulfate (CaSO3)

CaO + SO2 —→ CaSO3

neutralisation rxn

what does calcium carbonate react with sulphur dioxide to form

give an equation for this

what type of reaction is this

calcium sulfate (but now CaSO4)

CaCO3 + SO2 + 0.5O2 —→ CaSO4 + CO2

neutralisation

REMEMBER: ALL METAL SULFATES (E.G. BARIUM SULFATE) ARE SALTS!!!

common rules for solubility of salts? no syllabus requires these to be learnt but a good chemist does know them.

NOT EXACTLY REQ. BUT GOOD TO KNOW

general method to make an insoluble salt

he salt would be removed by filtration, washed with distilled water to remove soluble impurities and then dried on filter paper

how to write ionic eqs. for precipitation rxns