AS - group 7 Flashcards
What colour is fluorine?
pale yellow gas
what colour is chlorine?
yellow green gas
what colour is bromine?
dark red liquid
what colour is iodine?
shiny grey-black solid
What happens to the melting points of group 7 and why?
They increase as molecules get larger they have more electrons, so have stronger van der Waals so more energy is required to overcome
What happens to the electronegativity and why?
decrease as outer electrons are further from the nucleus and there is more shielding so less attraction
What ions would fluorine displace?
Cl-, Br-, I-
What ions would chlorine displace?
Br-, I-
What ions would bromine displace?
I-
What ions would iodine displace?
none
What colour would the solution turn if chlorine, bromine or iodine were present?
chlorine - yellow
bromine - orange
iodine - brown
E.g. ionic equation between chlorine and sodium bromide.
Cl2(aq) + 2Br-(aq) –> 2Cl- (aq) + Br2(aq)
what are example half equations for the displacement between chlorine and sodium bromide?
oxidation -
2Br- > Br2 + 2e-
reduction -
Cl2 + 2e- > 2Cl-
What is the strongest oxidising agent and why?
F2
-most likely to gain an e-
-smallest atomic radius
-less shielding
-more attraction between e- and nucleus
what is the strongest reducing agent and why?
iodide
-lose e- most easily
-largest atomic radius
-more shielding
-less attraction between e- and nucleus
How do you test for halides?
acidify with nitric acid and then add silver nitrate
When testing for halides, why do you acidify with nitric acid?
It reacts with any carbonates to prevent the formation of Ag2CO3, which would give a false result
What is the general equation for the test for halides, where X is the halide?
AgNO3 (aq) + NaX (aq) > AqX (s) + NaNO3 (aq)
What are the results when only silver nitrate has been added?
chloride > white ppt
bromide > cream ppt
iodide > yellow ppt
What are the results when dilute NH3 has been added?
chloride > colourless as soluble
bromide > cream, NVC
iodide > yellow, NVC
What are the results when conc. NH3 is added?
chloride > NVC, still colourless
bromide > soluble, colourless
iodide > NVC
What are the observations and their causes when potassium chloride reacts with conc. sulfuric acid?
misty fumes > displacement of CL-
Universal indicator goes red/orange
what is the equation when KCl reacts with H2SO4? Is it a redox and why?
H2SO4 + KCl > HCL + KHSO4
not a REDOX as oxidation states of halide and sulfur stay the same
What are the observations and their causes when potassium bromide reacts with conc. sulfuric acid?
misty fumes > displacement of Br-
brown vapour > oxidation of Br-
colourless gas > reduction of H2SO4
potassium dichromate paper goes green > SO2 made
What are the equations when KBr reacts with H2SO4?
H2SO4 + KBr > HBr + KHSO4
HBr - reducing agent
2HBr + H2SO4 > SO2 + Br2 + 2H2O
What are the observations and their causes when potassium iodide reacts with conc. sulfuric acid?
misty fumes > displacement of I-
purple vapour > oxidation of I-
colourless gas > reduction of H2SO4
yellow solid - sulfur
bad egg smell > H2S
potassium dichromate paper goes green > SO2
What are the equations when KI reacts with H2SO4?
H2SO4 + KI > HI + KHSO4
2HI + H2SO4 > SO2 + I2 + 2H2O
8HI + H2SO4 > H2S + 4I2 + 4H20
6HI + H2SO4 > S + 3I2 + 4H2O
Why is chlorine used in swimming pools?
to kill bacteria
What is the equation when chlorine is added to swimming pools?
Cl2 (g) + H2O <> HOCl (aq) + HCl (aq)
When chlorine is added to the swimming pools, has it been oxidised or reduced?
both, it undergoes disproportionation
What is the equation when chlorine is added in sunlight?
2Cl2 (g) + 2H2O (l) > 4HCl (aq) + O2 (g)
What is added due to the fact in sunlight, chlorine is rapidly lost? what is the equation?
solid sodium chlorate (I)
NaClO (s) + H2O <> Na+ (aq) + OH- (aq) + HClO (aq)
why are swimming pools kept slightly acidic?
In alkaline solution, eqm moves to the left and HClO is removed as ClO- ions
what is the equation when chlorine reacts with cold, dilute NaOH?
Cl2 (g) + 2NaOH (aq) > NaClO (aq) + NaCl (aq) + H2O (l)
what is the ionic equation when chlorine reacts with cold, dilute NaOH?
Cl2 (g) + 2OH- > ClO- (aq) + Cl- (aq) + H2O (l)
why is chlorine used in pools even though it can be toxic?
the health benefits outweigh the risks.
