Group 7 Flashcards
Identify a reagent that could be used to indicate the presence of iodide ions in an aqueous solution and describe the observation made.
AgNO3 yellow ppt
or
Cl2 or Br2brown solution/black ppt
What type of molecules are group 7 under normal conditions?
Diatomic molecules e.g. F2, Cl2, Br2
What are group 7 ions called?
- When they gain an electron to form 1- ions
- called halides e.g. F-, Cl-, Br-
Describe fluorine at room temperature
pale yellow gas
Describe chlorine at room temperature
pale green gas
Describe bromine at room temperature
- orange/brown liquid
- vaporises easily into an orange gas
Describe iodine at room temperature
- black solid
- vaporises to purple gas when heated
describe what happens to group 7 elements as you go down the group?
become darker and denser
describe trend in atom size as you go down group 7
- atoms get bigger
- shielding increases
describe trend in electronegativity as you go down group 7
electronegativity decreases
what 3 factors does electronegativity of group 7 elements rely on?
- nuclear charge
- atomic radius
- shielding
How does nuclear charge, atomic radius and shielding affect electronegativity?
- greater nuclear charge = withdraw electrons more strongly
- shorter atomic radius = helps withdraw electrons more strongly
- more shielding = reduce amount of electrons that can be withdrawn
What is the most electronegative element of group 7?
Fluorine
What is the least electronegative element of group 7?
Iodine
What type of IMF exists between group 7 molecules?
Van Der Waals
What can halogens act as?
Oxidising agents
What is the strongest oxidising agent of group 7?
- Fluorine
- accepts electrons most easily
What is the weakest oxidising agent of group 7?
- Iodine
- accepts electrons least easily
What happens during displacement reactions?
- highest element in group 7 forms halide ion
- halogen lowest down group 7 forms halogen molecule
Displacement reaction between chlorine and sodium bromide
Cl2 (aq) + 2NaBr (aq) —> 2NaCl (aq) + Br2 (aq)
OR
Cl2 (aq) + 2Br (aq) —> 2Cl- (aq) + Br2 (aq)
Reaction between potassium fluoride and chlorine
- no reaction
- F is higher than Cl
- F exists as ions
- Cl exists as molecules
Chlorine reacts with cold, dilute, aqueous sodium hydroxide.
Give a complete list of the names of the products?
- sodium chlorate (I)
- sodium chloride
- water
What type of solution is formed when chlorine is added to water
acidic
Why is chlorine added to water?
to kill bacteria
How is it possible to add chlorine to drinking water when chlorine is toxic?
only added at low concentrations
Complete the overall equation for the reaction between sodium chlorate (I) and water
NaCl (aq) + H2O (l) —> Na+ (aq) + OH- (aq) + HClO (aq)
Complete the overall equation to show the reaction of chlorine gas with an alkaline solution
Cl2 (aq) + 2NaOH (aq) —> NaCl (aq) + NaClO (aq) + H2O (l)
What halide would be present following these observations?
“To the unknown sample, a few drops of nitric acid (HNO3) were added. Following this, a few drops of Silver Nitrate solution (AgNO3) were added and a yellow precipitate was formed. This precipitate remained after the addition of dilute and concentrated ammonia (NH3)”
iodide ions
What halide would be present following these observations?
“To the unknown sample, a few drops of nitric acid (HNO3) were added. Following this, a few drops of Silver Nitrate solution (AgNO3) were added and a white precipitate was formed.”
chloride ions
What halide would be present following these observations?
“To the unknown sample, a few drops of nitric acid (HNO3) were added. Following this, a few drops of Silver Nitrate solution (AgNO3) were added and no precipitate was observed forming.”
fluoride ions
What halide would be present following these observations?
“To the unknown sample, a few drops of nitric acid (HNO3) were added. Following this, a few drops of Silver Nitrate solution (AgNO3) were added and a cream precipitate formed. This precipitate remained upon addition of dilute ammonia (NH3). but dissolved when concentration ammonia was added.”
bromide ions
Select all the following observation(s) that would be present in the reaction with NaI(s) and H2SO4(aq).
- acidic gas forms (SO2)
- gas smelling of bad eggs formed (H2S)
- black solid forms (I2)
- yellow solid formed (sulfur)
Solid sodium chloride reacts with concentrated sulfuric acid.
Give an equation for this reaction.
State the role of the sulfuric acid in this reaction.
NaCl + H2SO4 —> NaHSO4 + HCl
Proton donor
Fumes of sulfur dioxide are formed when sodium bromide reacts with concentrated sulfuric acid.
For this reaction
* give an equation
* give one other observation
* state the role of the sulfuric acid.
equation:
2NaBr + 2H2SO4 —> Na2SO4 + SO2
observation:
brown gas/brown fumes or orange gas/orange fumes
role:
oxidising agent
Give the oxidation state of chlorine in NaClO3 and in NaCl
NaClO3
+5
NaCl
-1
State one observation when solid sodium chloride reacts with concentrated sulfuric acid.
[1 mark]
[3 marks]
0 9 . 3
Give an equation for the reaction.
State the role of the chloride ions in the reaction.
M1 Misty or steamy or white fumes/gas
M2 NaCl + H2SO4 → NaHSO4 + HCl OR
2NaCl + H2SO4 → Na2SO4 + 2HCl M3 Base OR proton acceptor
State one observation when solid sodium chloride reacts with concentrated sulfuric acid.
Give an equation for the reaction.
State the role of the chloride ions in the reaction.
M1 Misty or steamy or white fumes/gas
M2 NaCl + H2SO4 → NaHSO4 + HCl OR
2NaCl + H2SO4 → Na2SO4 + 2HCl M3 Base OR proton acceptor
strongest oxidising agent
F-
weakest oxidising agent
I-
flouride with sulphuric acid
NaF (s) + H2SO4 (aq) —> NaHSO4 (s) + HF (g)
steamy fumes of HF gas produced
chloride with sulphuric acid
NaCl (s) + H2SO4 (aq) —> NaHSO4 (s) + HCl (g)
steamy fumes of HCl gas
bromide with sulphuric acid
NaBr (s) + H2SO4 (aq) —> NaHSO4 (s) + HBr (g)
2Br- —> Br2 + 2e-
2H+ + H2SO4 + 2e- –> SO2 + 2H2O
OVERALL EQUATION
2br- + 2h+ + H2so4 —> br2 + so2 + 2h2o
iodide with sulphuric acid
NaI (s) + H2SO4 (aq) —> NaHSO4 (s) + HI (g)
- 2I- —> I2 + 2e-
2H+ + H2SO4 + 2e- –> SO2 + 2H2O
overall equation
2H+ + H2SO4 + 2I- —> SO2 + 2H2O + I2
acidic gas and black iodine solid forms - 2I- —> I2 + 2e-
6H+ + H2SO4 + 6e- –> S + 4H2O
overall equation
6I- + H2SO4 + 6H+ —> 3I2 + S + 4H2O
yellow solid sulfur and black iodine solid forms - 2I- —> I2 + 2e-
8H+ + H2SO4 + 8e- —> H2S + 4H2O
overall equation
4I- + 8H+ + H2SO4 —> H2S + 4I2 + 4H2O
gas smelling of bad eggs and black iodine solid forms
testing for halides
- add HNO3 to unknown sample
- add few drops of silver nitrate solution
- ppt forms
fluoride ions test
NVC
AgF (aq)
chloride ions test
- HNO3 and AgNo3
white ppt AgCl (s) - dilute ammonia
white ppt dissolves - conc ammonia
white ppt dissolves
bromine ions test
- HNO3 and AgNo3
cream ppt AgBr (s) - dilute ammonia
cream ppt remains - conc ammonia
cream ppt dissolves
iodide ions test
- HNO3 and AgNo3
white ppt AgI (s) - dilute ammonia
yellow ppt remains - conc ammonia
yellow ppt remains
uses of chlorine
kills bacteria
chlorine and water
Cl2 (g) + H2O (l) —> HClO (aq) + HCl (aq)
- disproportionation
- chlorine goes through oxidation and reduction
chlorine reaction in presence of sunlight
2Cl2 (g) + 2H2O (l) —> 4HCl (aq) + O2 (g)
cl2 = pale green
Hcl = colourless
NaClO and H2O reaction
NaClO(s) + H2O(l) —> Na+(aq) + -OH(aq) + HClO(aq)
- reversible reaction
- added to swimming pools
chlorine and sodium hydroxide reaction
Cl2 (g) + 2NaOH (aq) —> NaClO (aq) + NaCl (aq) + H2O (l)
