Group 7 Flashcards
Sodium bromide reacts with concentrated sulfuric acid in a different way to sodium chloride. Give an equation to represent this reaction MS [1]
2NaBr + 2H2SO4 —> Na2SO4 + Br2 + SO2 + 2H2O
Explain why dilute hydrochloric acid is not used to acidify the silver nitrate solution in a test for iodide ions: MS [1]
HCl would form a white precipitate (Cl- reacts with Ag+)
State why the silver nitrate solution is acidified when testing for iodide ions: MS [1]
- They react with ions that would otherwise interfere with the test
- To prevent formation of other soluble silver precipitates
- To remove other ions that react with silver nitrate
State the trend in the boiling points of the halogens from fluorine to iodine and explain this trend: MS [4]
- Increase
- Van der Waals forces between molecules
- Increase in strength with size
- More energy is needed to break stronger bonds
Explain how the addition of an ammonia solution can be used to confirm that a precipitate is silver bromide: MS [2]
Concentrated ammonia
Will dissolve the precipitate
Suggest why iodide ions are stronger reducing agents than chloride ions: MS [2]
- Iodide ions are larger, with more electron shells and a larger atomic radius
- The outer electron to be lost is less strongly attracted and held by the nucleus
NaClO
NaClO3
K2SO4
K2SO3
- Sodium Chlorate (I)
- Sodium Chlorate (V)
- Potassium Sulfate (VI)
- Potassium Sulfate (IV)
Give the equation for when Silver Chloride dissolves in ammonia solution
AgCl(s) + 2NH3 (aq) –> [Ag(NH3 )2 ]+ (aq) + Cl - (aq)
How is chlorine involved in bleach production?
Chlorine can be mixed with cold, aqueous sodium hydroxide to produce sodium hypochlorite.
Cl2 + 2NaOH –> NaCl + NaClO + H20
The mixture of NaCl and NaClO is used as a key ingredient in the production of bleach.
What are the uses of chlorine?
They can be used in small quantities to kill bacteria in water treatment processes.
This poses some risks as chlorine can be otxic, however the benefits of clean,treated water outweigh the risks.
How does chlorine react with water in the precense of UV light?
Chlorine decomposes water to produce Oxyge and HCl.
2Cl2+ 2H2O –> 4HCl + O2
How does Chlorine react with cold water?
Cl2+ H2O –> ClO-+ Cl- +2H+
How does iodide react with concentrated sulphuric acid?
They are the strongest reducing agents. They can reduce sulfur from +6 in H2S)4 to +4 in SO2 to 0 in S and -2 in H2S.
Observations:
HI - White Steamy Fumes
I2 - Black Solid / Purple Fumes
SO2 - Colourless, Acid Gas
S - yellow Solid
H2S - Rotten egg smell
How does bromide react with concentrated sulphuric acid?
Br- are stronger reducing agent, so can react further after the intial acid-base reaction. It reduces Sulfur in H2SO4from +6 to +4 in SO2.
Observations:
White Steamy fumes of HBr
Orange Fumes of Br
Colorless, Acidic Gas of SO2
How does the reducing power of halides change as you go down the group?
Reducing power of the halide increases down group 7 as they have a greater tendency to lose electrons.
This is because ions get bigger, and shielding increases, it is easier for electrons to be removed.
If the results of the silver nitrate test are too similar, what further treatment can we do to differentiate between the ions?
Treat further with ammonia solution.
1. Silver Chloride dissolves in dilute ammonia
2. Silver Bromide dissolves in concentrated ammonia
3. Silver Iodide does not react with ammonia
note that solution produced with Br- and Cl- is colorless
What is the role of nitric acid in the silver nitrate test for halide ions?
Reacts with any carbonates to prevent formation of the precipitate Ag2CO3. This would mask the desired observations.
What are the observations in the silver nitrate test for each type of halide ion?
Fluorides produce no precipitate
Chlorides produce a white precipitate
Ag+ (aq) + Cl - (aq) -> AgCl(s)
Bromides produce a cream precipitate
Ag+ (aq) + Br- (aq) -> AgBr(s)
Iodides produce a pale yellow precipitate
Ag+ (aq) + I- (aq) -> AgI(s)
How do we test for various halide ions?
The test solution is made acidic with nitric acid, and then silver nitrate solution is added dropwise.
What are the colours of solution for each type of free halogen?
Chlorine = Pale Green (often colourless)
Bromine = Yellow/Orange Solution
Iodine = Brown Solution
What are the rules of displacement for group 7?
- Chlorine will displace both Br- and I-
- Bromine will displace I-
How does reactivity change down group 7?
Reactivity in group 7 is measured by their oxidising strength (to gain 1 electron to get a full outer shell)
Hence, it decreases down a group as
1) Atomic radii increases
2) Greater number of shells
What is the trend in electronegativity down group 7?
Down the group, electronegativity will decrease.
This is because:
1. Atomic radii increase
2. Greater shielding
Therefore, the attractive force of the nucleus decreases.
What is the trend in m.p/b.p down group 7?
Increases down the group
As the molecules become larger, they have more electrons and so have stronger VDW forces between the molecules.
As the forces get larger, more enerrgy has to be put in to break the forces.
