2.4 GROUP 2 Flashcards
to learn the trends
solubility of G2 hydroxides
solubility trend: increases
Mg( OH )2 insoluble
Ca( OH )2 slightly soluble
*the above have ionic eq
Sr(OH)2 soluble
Ba(OH)2 soluble
solubility of G2 sulfates
solubility trend: decreases
MgSO4 soluble
CaSO4 slightly soluble
SrSO4 insoluble
BaSO4 insoluble
*the above have ionic eq
solubility trend of G1 hydroxides and sulfates
no trends
because all soluble
why group 1 and 2 metals are called as s block elements?
as the highest occupied energy level is the s-orbital
trend in first ionization energy of G2
trend: decreases
explanation:
down the group, the proton increases but the shielding effect of inner shells electrons increases too.
however, the outer shell electron is further away from nucleus.
which weakens the force of attraction and less energy is needed to remove an electron
trends down G2
melting point
electrical conductivity
reducing power
reactivity
melting point: decreases, weaker metallic bond
electrical conductivity: increases, easier to form delocalised electrons
reducing power: increases , ionisation energy decreases easier to lose electron and from cation
reactivity : increases , easier to form cation
group 2 + oxygen
form oxides
refer note
group 2 + water
form hydroxides
refer note
group 2 + chlorine
form chlorides
refer note
state the acid-base nature of G2 oxides
basic oxides
except BeO is amphoteric
non metal oxides are acidic like CO2, NO2
unlike magnesium why barium is kept immersed under paraffin oil or in vacuum sealed ampoules
barium is very reactive
readily react with O2 and moisture in air
turns into liquid when exposed to air
lithium chloride can be made by burning lithium in chlorine. why rubidium chloride is not prepared like that
rubidium is more reactive
is vigorous and therefore dangerous
bonding present in BeCl2
covalent
bonding present in BaCl2
ionic
why the type of bonding is different for BeCl2 and BaCl2
BeCl2
Be 2+ is small and highly polarising and therefore greater distortion of electron clouds on chlorides
hence, shows greater covalent character
BaCl2
large electronegativity difference between Ba and Cl2
hence shows greater ionic character
compare the reaction of g2 hydroxides and and oxides
see notes pg4
how to make metal hydroxides give three ways
g2 plus water
g2 oxides except Beo plus water
g2 salt plus base like NaOH
which g2 sulfates is least soluble
BaO4
state the use of insolubility of sulfates in medical field and lab test
refer to notes pg5
why strontium stops reacting with dilute sulphuric acid after a few seconds even though they react initially
strontium and sulphuric acid forms insoluble strontium sulphate. forms a layer around the Sr metal prevent further reaction with acid
barium with cold water
barium hydroxide (aq) plus hydrogen
aqueous solution of barium hydroxides to a pure sample of barium sulphate
barium hydroxides react with excess sulphuric acid to ensure all barium hydroxide convert completely to BaSO4
filter the solution using filter paper
soild obtain is pure barium sulphate
wash
pat dry do not heat cause g2 decompose under heat
Mg(Cl)2 + excess NaOH
all aq
percipitation
ionic eq form
white percipitate is form
insoluble in excess NaOH
not amphoteric
Ba(Cl)2 + excess NaOH
all aq
no ionic eq
no percipitate
remains clear
flame test Li+ Na+ K+ Rb+ Ca+ Sr+ Ba+
Li+ deep red
Na+ golden yellow
K+ lilac
Rb+ bluish red
Ca+ brick red
Sr+ crimson red
Ba+ green
flame test method
refer notes
explanation for flame colour
refer notes
why platinum or nichrome wire is used in flame test
unreactive with conc HCL it is dipped in
will not give a flame colour of its own
why conc HCL is used not H2SO4 and HNO3
reacts with salt and forms metal chlorides
chlorides are much mire volatile than sulfates or nitrate
why is it necessary to clean the wire by repeatedly dipping in conc HCL and heat prior testing
to ensure no traces of metal ions remain
that would produce a flame colour which lead to false observation
why is it impossible to identify K+ ions in a sample contaminated with small amounts of Na +
the intense yellow flame will mask the pale lilac flame
thermal decomposition
meaning
use of heat to break down a single reactant into 2 or more simpler products
the higher the thermal stability, the higher the temp needed to decompose it
g1 carbonates
effect of heat
general eq
trend in thermal stability
effect of heat: do not decompose
general eq: no
trend in thermal stability: very stable
g2 carbonates
effect of heat
general eq
trend in thermal stability
effect of heat: decompose to give metal oxide and co2
general eq: refer notes
trend in thermal stability: increases
does g1 hydrogencarbonates decomposes under heat?
yes
eq refer notes
experiment diagram to investigate thermal stability
refer notes pg 8
how experiment for thermal stability helps to explain thermal stability
time taken foe lime water to turn cloudy
experiment diagram to investigate thermal stability
how you would control the factors in the experiment so diff carbonates can be compare
- constant bunsen flame
2.fixed height of test tube above flame - fixed moles or mass of carbonates
- fixed volume of limewater
same cloudiness of limewater
experiment diagram to investigate thermal stability
this experiment gives only approximate results
suggest an alternative improvement to increase the reliability
collect and measure the volume of co2 using a syringe for a fixed Heating time
weigh the solid before and after heating to determine the change in mass or a fixed amount of heating time
g1 nitates
effect of heat
general eq
trend in thermal stability
experimental evidence
effect of heat: decompose to give metal nitrate and o2
general eq : refer notes pg 9
trend in thermal stability: increases
experimental evidence: time taken for the solid to melt
g2 nitates
effect of heat
general eq
trend in thermal stability
experimental evidence
effect of heat: decompose to give metal oxide, nitrogen dioxide amd o2
general eq: refer notes
trend in thermal stability: increases
experimental evidence: time taken for appearance of brown gas and time taken for solid to melt
the thermal stability of ionic compounds depends on
ionic charge of cation
ionic radius of cation
down g2 carbonates and nitrate increases because
cation radius increases but charge remains the same
polarising power of cation decreases
difficult to distort electron cloud on anion / more energy is needed to weaken the bond
why MgO2 cannot be further decomposed to Mg and O2?
O2- is small and high charge
there fore O2- cannot be easily polarised
why G1 carbonates are more stable than G2 carbonates
g1 metal ion is less polarising than g2 metal ion
less distortion of electron cloud on CO3 2-
more energy is needed to break the bond in g1 carbonates
calcium plus water
calcium hydroxide and hydrogen
state the trend in solubilty of g2 hydroxides
increases
why MgCl2 does not produce a flame colour
the radiation is not in the visible light range
polarising power
meaning
the ability of cation to distort the electron cloud of cation
radium hydroxide soluble in water?
yes
radium sulphate soluble in water?
no
