Group 7 - The Halogens Flashcards
What does F2 look like
Pale yellow gas
What does Cl2 appear as
A pale green gas
How does Br2 appear
Dark red/ brown/ orange liquid
How does I2 appear
Dark purple/ black solid
What is the trend in atomic radius for group 7
Increases down the group
What is the trend in electronegativity for group 7
Why?
Decreases down the group
Size increases
More shielding
So ability of nucleus to attract electrons is reduced
What is the trend in boiling point for group 7
Why
Boiling point increases down the group
All halogens are diatomic and as you go down the group the size of the atom increases and there are more Van der Waals forces between molecules
Halogens act as oxidising agents
True or false?
True
What happens when a halogen acts as an oxidising agent
Each halogen Atom gains an electron
What is the trend in the ability as an oxidising agent in group 7
Why
Decreases down the group
Atomic radius increases down the group and shielding increases
Halogen atom gains an electron less readily
Method to test displacement reaction
Aqueous solutions of the halogens are added drop-wise to a colourless solution containing halide ions; solutions of Potassium Chloride, Potassium bromide, and potassium iodide are usually added as the salts
What observations are seen when Cl2 is added to potassium bromide
Why?
Ionic equation for this reaction
Yellow/ brown solution of Br2
Cl2 oxides Br-
2Br- +Cl2 —>2Cl- +Br2
Observation for Cl2 added to potassium iodide
Why
Give ionic equation
Brown solution/ black PPT
Cl2 oxides I-
2I- +Cl2 —> 2Cl- +I2
Observations for Br2 + KCl
Why
No visible change
Br2 is not able to oxidise Cl2
Observation for Br2 + KI
Brown solution/ black PPT
Br2 oxidises I-
2I- + Br2 —> 2Br- + I2
Observation for I2 added to KCl
No visible change
I2 is not able to oxidise Cl-
What can chlorine oxidise
Br- and I-
What can Bromine oxidise
I- but not Cl-
What will iodine oxidise
Neither Cl- nor Br-
Which halogens are the strongest and weakest oxidising agents
F2 is the strongest
I2 is the weakest
Trend in ability of a halide ion to act as a reducing agent
Increases down group 7
How is trend in reducing powers of halide ions shown?
Reaction of solid halide salts with concentrated sulphuric acid
Oxidation state of S in H2SO4
+6
What can the S in H2SO4 be reduced to
+4, 0, or -2 depending on reducing power of the halide ion
What is produced from NaF + H2SO4
What redox reaction occurs
Na2SO4 + 2HF
No redox reaction occurs as F- is not a strong enough reduction agent to reduce S in H2SO4
Cl- is the same
Acid-base reaction for NaBr + H2SO4
Redox reaction of NaBr to give SO2 and half equation
2NaBr + H2SO4—> Na2SO4 + 2HBr
2H+ + H2SO4 + 2Br- —> Br2 + SO2 + 2H2O
2e- +2H+ +H2SO4 —> SO2 + H2O
Equation for NaI + H2SO4 acid base reaction
2NaI + H2SO4–> Na2SO4 +2HI
What are the 3 different products from the 3 redox reactions for NaI + H2SO4
SO2 - choking gas
S - yellow solid
H2S - smell of rotten eggs
How to identify HF, HCl, HBr, and HI (observation)
Misty fumes
Observation for production of Br2
I2?
Brown gas
Black solid/ purple gas
Equation for redox reaction including I- to produce SO2
2H+ + H2SO4 + 2I- —> SO2 + 2H2O + I2
I- redox reaction to produce S
6H+ + H2SO4 + 6I- —> S +4H2O + 3I2
I- redox reaction to produce H2S
H2SO4 + 8H+ +8I- —> 4I2 + H2S + 4H2O
Strongest and weakest reducing agents of Halogens
Strongest = I- Weakest = F-
Which silver halides are soluble and insoluble
Soluble: Silver fluoride
Insoluble: silver chloride, bromide, iodide
Why is HNO3 added to an aqueous halide solution before silver nitrate test
To remove hydroxides and carbonates that would form a precipitate
What colour PPT does each halide produce when added to AgNO3 and how soluble are they in NH3
F- : none as AgF is soluble
Cl-: white; soluble in dilute NH3
Br-: cream; partially soluble in dilute NH3, soluble in conc NH3
I-: yellow; insoluble in conc NH3
What is formed when Cl2 is dissolved in water
HCl and chloric acid (HClO)
Equation for Cl2 dissolving in water
Is Cl2 oxidised or reduced?
What is the equilibrium mixture called and what colour is it
Cl2+H2O (equilibrium sign) HCl + HClO
Both this is called disproportionation
Chlorine water
Pale green
What colour does litmus paper turn in chlorine water
Why
Red as Both reaction products are acidic
Red then disappears and the UI turns white because HClO is a v effective bleach
Equation for chlorine and water in bright sunlight
What is oxidised and reduced
2Cl2 + 2H2O—> 4HCl + O2
Chlorine oxidises water to O2
Chlorine is reduced to chloride ions
Why does chlorine water’s green colour fade in bright sunlight
Cl2 is converted to HCl and O2 which are colourless
Chlorine is toxic. Why is it still used to disinfect water
Health benefits outweigh the risks
Equations for chlorine reacting with cold dilute NaOH
Cl2 +2NaOH—> H2O + NaCl + NaClO
Cl2 +2OH- —> H2O + Cl- +ClO- (ionic equation)
Why is Cl2 + NaOH of great commercial importance
NaClO is the active ingredient in household bleach
Test for CO3 2- ions
Add HCl
CO2 gas given off (effervescence)
Test for NH4+
Warm carefully
Do not allow to spit
Ammonia gas given off
Which will turn damp litmus blue
Test for Ba2+
Add sulphuric acid
White ppt of barium sulphate produced
Test for OH-
Add magnesium chlorine
White ppt of magnesium hydroxide formed
Or
Add universal indicator
Turn blue
What must always be included when writing equations for group two metals and water
State symbols
When testing for halides what state must they be in
Aqueous
If a procedure asks the product to be pure what must you include
Filter
Wash
Dry
2 things to mention when discussing reducing ability
Size of ion
Attraction of nucleus to e-
Colour of Br(2) as gas
BROWN gas
Colour of I2(g)
PURPLE gas
Normal reaction of chlorine and water
Cl2 + water —-> HCl + HClO
Disproportionation
What are the products of mixing Cl2 and water
HCl Chloric acid (a weak acid)
Chlorine in sunlit water
Cl2 + H2O —-> HCl + O2
Pale Green Colourless
Products of Cl2 + water in sunlight
HCl
O2
Observation when Cl2 is added to KBr
Yellow/ brown solution
Observation when Cl2 is added to I-
Black PPT
dark brown solutions
Observation when Br2 is added KI solution
Black PPT
Dark brown solution
