Group 2 And 7 Flashcards
Atomic radius - 2
Increases
-NO. Principal energy levels increases
- Shielding increases
- less attraction between Valence e- and nucleus
First IE down group 2
Decreases
- NO. Principal E levels increases
- shielding increases
- weaker attraction between valence e- and nucleus
Melting point down group 2
Decreases
- size of ion increases
- weaker electrostatic forces of attraction between positive ions and delocalised e-
Group 2 + water reactivity down group
-More reactive down group
-atomic radius increases
- shielding increases
- reactivity increases
More vigorous, warmer, more ppt
Group 2 + water eqn
X + H2O -> X(OH)2 +H2
Mg with steam
Mg + H2O -> MgO + H2
s. g. s. g
White solid white flame
Solubility of group 2 hydroxides (not explanation)
Mg - very sparingly white ppt
Ca - sparingly White ppt
Sr - slightly
Ba - soluble
Group 2 hydroxides pH
Mg 8-9
Ca 10-11
Sr 11-12
Ba 13-14
More OH- ions in solution
Test for Mg 2+ ions in solution
(Sodium) hydroxide + solution with Mg2+
- white ppt of Mg(OH)2
MgCl2 + 2NaOH-> Mg(OH)2 + 2NaCl
Aq. Aq. S. Aq
Mg2+ + 2OH- -> Mg(OH)2
Aq. Aq. S
Test for OH- ions in solution (group 2)
Magnesium (chloride) solution + solution with OH-
White ppt of Mg(OH)2
MgCl2 + 2NaOH-> Mg(OH)2 + 2NaCl
Aq. Aq. S. Aq
Mg2+ + 2OH- -> Mg(OH)2
Aq. Aq. S
Test for Ba2+ ions in solution
Sulphuric acid + barium ions
White ppt
H2SO4 + BaCl2 -> BaSO4 + 2HCl
Aq. Aq. S. Aq
SO4 ²- + Ba2+ -> BaSO4
Aq. Aq. S
Test for SO4 ²- ions in solutions
ACIDIFIED barium (chloride) + sulfate ions
Na2SO4 + BaCl2 -> BaSO4 + 2NaCl
Aq. Aq. S. Aq
SO4 ²- + Ba2+ -> BaSO4
Aq. Aq. S
Why does barium chloride have to be acidified in a sulphate ion test
With HCl or HNO3
- Remove carbonate ions that would give false positive
2H+ + CO3 ²- -> CO2 + H2O
BaCO3 formed
Uses of Mg(OH)2
Neutralises, excess stomach acid
CaCO3 not used as produces CO2
Ca(OH)3 uses
Neutralises acidic soils
CaO & CaCO3 uses
Fluegas desulphurisation
Neutralises SO2
CaO + SO2 -> CaSO3
BaSO4 uses
CT scans/x-rays
Barium meal, damaged areas of digestive tract seen
Insoluble
BaCl2 uses
Test for sulphate in solutions
Ba²- + SO4²- -> BaSO4
Uses of Mg
Extraction of titanium
Process of titanium extraction
Rutile ore high temp
TiO2 + 2Cl2 + 2C -> TiCl4 + 2CO
S. G. S. G. G
Magnesium used as reducing agent heated, atmosphere of argon (inert)
TiCl4 + 2Mg -> Ti 2MgCl2
Halogens as oxidising agents
Down group, less oxidising
-Size increases
-more shielding
-Gain electrons, less readily
-weaker attraction from nucleus
Cl2 + 2NaBr
-> 2NaCl + Br2 (yellow)
Cl2 + 2NaI
-> 2NaCl + I2 (brown)
Br2 + 2NaI
-> NaBr + I2 (brown)
Br2 + 2NaCl
NVC
I2 + 2NaBr
NVC
I2 + 2NaCl
NVC
Test for halide ions eqn
AgNO3 + NaX -> AgX NaNo3
Ag+ + X- -> AgX
AgNO3 + NaF
NVC
AgNO3 + NaCl
White ppt
AgNO3 + NaBr
Cream ppt
AgNO3 + NaI
Yellow ppt
Silver halides with dilute ammonia
AgX + 2NH3 -> Ag(NH3) + X-
AgCl - soluble
AgBr - sparingly
AgI - insoluble
Silver halides with concentrated ammonia
AgX + 2NH3 -> Ag(NH3) + X-
AgBr - soluble
AgI - insoluble
Why does AgNO3 need to be acidified when testing for halide ions
To remove hydroxide and carbonate ions, which would form ppt with Ag+
Add dilute nitric acid
2HNO3+Na2CO3 ->2NaNO3+CO2+H2O
Cant use HCl, has Cl
Halide ions as reducing agents
Acid base
Eqn
NaX + H2SO4 -> NaHSO4 + HX ( misty fumes)
2NaX + H2SO4 -> NaSO4 + 2HX
Explain reducing ability of group 7 elements
Increases down the group
- Size of ion increases
-Shielding increases
-Outer e- further away from nucleus
-So less attraction
- ions lose e- more readily
Br- ions as reducing agents
Redox
Br- -> Br2 (Brown Gas)
H2SO4 -> SO2 (Chocking gas)
I- ions as reducing agents
Redox
I- -> I2. ( black solid, purple Gas)
H2SO4 -> SO2. ( choking gas)
H2SO4 -> S. ( yellow solid)
H2SO4 -> H2S. ( rotten egg smell)
Form of Br2
Brown gas
Form of SO2
Choking gas
Form of I2
Black solid purple Gas
Form of S
Yellow solid
Form of H2S
Rotten egg smell
Electronegativity of group, 7
Decreases down the group
- NO. Principle E levels increases
- Weaker attraction between valence e- and nucleus in covalent bond
BP of group, 7
Increases down the group
- size of atom increases
- more VdW forces between molecules to be broken
Chlorine and water equation
Cl2 + H2O -> HCl + HClO
g. l. Aq. Aq
Chlorine water (info)
Disproportionation
Universal indicator, paper turns red, then bleached white by HClO
Chlorine and water and bright sunlight equation
2Cl2 + 2H2O -> 4HCl + O2
G
Chlorine bubbled through water
Chlorine with sodium hydroxide equation
Cl2 + 2NaOH -> H2O + NaCl + NaClO
Cl2 + 2OH- -> H2O + Cl- + ClO-
State of F2
Pale yellow gas
State of Cl2
Pale green gas
State of Br2
Dark red liquid
State of I2
Dark purple solid
What do you use carbonate ions to test for? (Na2CO3)
Acids
release CO2 H2O
Effervescence
What do you use sulphate ions to test for? (Na2SO4)
Barium ions
White ppt
What do you use hydroxide ions to test for? (NaOH)
Magnesium ions
White ppt
Magnesium hydroxide is insoluble
What is the test for ammonium ions?
Ammonium containing salt, heated with aqueous sodium hydroxide
Produces ammonia, gas
Turns moist litmus paper blue
(NH4)+ + OH- -> NH3 +H2O