T3: Group 2 and Group 7 Flashcards
reducing agent
electron donor
reducing strength of halides
- increases down the group
- ionic radius increases
- weaker attraction between outer e- and nucleus
H2SO4 -> SO2
Br2, I2 - acidic chocking gas
H2SO4 -> S
I2 - yellow solid
H2SO4 -> H2S
I2 - bad egg smell
Role of H2SO4 with Br2, I2
oxidising agent
iodine half equation
2I- -> I2 + 2e-
I2 appears as…
a black solid
bromine half equation
2Br- -> Br2 + 2e-
Br2 appears as…
brown fumes
H2SO4 -> SO2 half equation
2e- + 2H+ H2SO4 -> SO2 + 2H2O
H2SO4 -> S half equation
6e- + 6H+ H2SO4 -> S + 4H2O
H2SO4 -> H2S half equation
8e- + 8H+ H2SO4 -> H2S + 4H2O
Role of H2SO4 with F, Cl
an acid
flourine half equation
H+ + F- -> HF
flourine observation
misty fumes
NaF + H2SO4 ->
NaHSO4 + HF
chlorine half equation
H+ + Cl- -> HCl
chlorine observation
misty fumes
NaCl + H2SO4 ->
NaHSO4 + HCl
NaBr + H2SO4 combined half equation (SO2)
2Br- + 2H+ + H2SO4 -> SO2 + Br2 + 2H2O
NaI + H2SO4 combined half equation (S)
6I- + 6H+ + H2SO4 -> S + 3I2 + 4H2O
NaI + H2SO4 combined half equation (H2S)
8I- + 8H+ + H2SO4 -> H2S + 4I2 + 4H2O
procedure to identify halide tests
1 dissolve sample in water (in not already in aq solution)
2 add HNO3 acid
3 add AgNO3(aq) solution
4 if halide is present you will see one of the observations
F- = no precipitate
Cl- = white precipitate
Br- = cream precipitate
I- = yellow precipitate
2 reasons why is HNO3 acid added
1 used to remove any possible CO32- impurities, which could give a false positive
2 DON’T use HCL or H2SO4 acid for this step
what 2 reactions (2 equations) will happen if you fail to remove any possible CO32- impurities, which could give a false positive
2Ag+(aq) + CO32-(aq) -> Ag2CO3(s) [WHITE precipitate]
2H+(aq) + CO32-(aq) -> CO2(g) + H2O(l) [EFFERVESCENCE]
what is the problem with the 1st observations seen in the test tubes (halide tests)
it can be difficult to tell whether you have a white, cream or yellow ppt
what happens because of the problem of these observations (halide tests)
further steps are carried out to positively identify the halide
what are the further steps that are carried out (for 2nd observation - halide tests)
add dilute NH3 to the sample
Cl- = white precipitate dissolves
Br- = cream precipitate insoluble
I- = yellow precipitate insoluble
what are the further steps that are carried out (for 3rd observation - halide tests)
add concentrated NH3 to the sample
Br- = cream precipitate dissolves
I- = yellow precipitate insoluble
what are the precipitates (AgNO3 - 4 ionic equations - halide tests)
Ag+(aq) + F-(aq) -> AgF(aq)
Ag+(aq) + CL-(aq) -> AgCl(s)
Ag+(aq) + Br-(aq) -> AgBr(s)
Ag+(aq) + I-(aq) -> AgI(s)
What does the NH3 do? (halide tests)
AgCl(s) + 2NH3(aq) -> [Ag(NH3)2]+(aq) + Cl-(aq)
AgBr(s) + 2NH3(aq) -> [Ag(NH3)2]+(aq) + Br-(aq)
Summary of Halide Tests
trend of oxidising ability of halogens
- decreases down group
- larger radius
- weaker attraction between nucleus and outer e-
3 ionic equations for halogen displacement reactions (halogens and halides)
Cl2 + 2Br- -> Br2 + 2Cl-
Cl2 + 2I- -> I2 + 2Cl-
Br2 + 2I- -> I2 + 2Br-
bromine observation in halogen displacement reactions
orange solution
iodine observation in halogen displacement reactions
brown solution
summary of halogen displacement reactions (halogens and halides)
why is chlorine added to water
to kill bacteria
why is chlorine added in low conc
its toxic
Cl2 + H2O ⇌
HCL + HCLO
what type of reaction is this: Cl2 + H2O ⇌ HCl + HClO
- disproportionation
- Cl2 reduced to HCl (OXS change 0 to -1)
- Cl2 oxidised to HClO (OXS change 0 to +1)
the reactivity of Group 2 metals…
increases down the group
group 2 with liquid water reaction where X is metal
X(s) + 2H2O(l) -> X(OH)2(aq) + H2(g)
Mg reaction with steam
Mg(s) + H2O(g) -> MgO(s) + H2(g)
observations of this reaction: Mg(s) + H2O(g) -> MgO(s) + H2(g)
white solid produced (MgO)
bright white light
equation for Mg reaction to extract Ti from TiCl4
TiCl4 + 2Mg -> 2MgCl2 + Ti
role of Mg in this reaction: TiCl4 + 2Mg -> 2MgCl2 + Ti
Mg OXS changes from 0 to +2
Mg is oxidised -> reducing agent
solubility of group 2 hydroxides…
increases down the group
simplest ionic equation (group 2 hydroxides)
Mg2+(aq) + 2OH-(aq) -> Mg(OH)2(s)
observation of this reaction: Mg2+(aq) + 2OH-(aq) -> Mg(OH)2(s)
white precipitate forms
what could you use to test for the presence of Mg2+ ions in a solution
NaOH(aq)
what could you use to test for the presence of OH- ions in a solution
Mg(NO3)2(aq)
uses of magnesium hydroxide
- indigestion relief
- often called ‘milk of magnesia’
- neutralises stomach acid
solubility of group 2 sulphates…
decreases down the group
simplest ionic equation (group 2 sulphates)
Ba2+(aq) + SO42-(aq) -> BaSO4(s)
observation of this reaction: Ba2+(aq) + SO42-(aq) -> BaSO4(s)
white precipitate forms
what could you use to test for the presence of Ba2+ ions in a solution
H2SO4(aq)
what could you use to test for the presence of SO42- ions in a solution
BaCl2(aq) ACIDIFIED
uses of barium sulphate
- stomach X-rays
- barium meal
- insoluble -> wont kill you