GROUP 7 Flashcards
What is the appearance and reactivity of fluorine?
very pale yellow gas.It is highly reactive
What is the appearance and reactivity of chlorine
Greenish ,reactive gas, poisonous in high concentration.
State the trends in melting point and boiling point down G7:
Increases down the group.
As the molecules become larger they have more electrons and so have larger van der waals forces so more energy required to break forces.Also down a group physical state changes from gas ,liquid to solid.
State the trends in electronegativity down G7:
Electronegativity decreases.
The atomic radius increases and the outer electrons are further from the nucleus as the shielding increases.The nucleus is therefore
less able to attract the bonding pair of electrons.
What is a displacement reaction?
A more reactive halogen will displace the halide ion of a less reactive halogen from solution.
What colour is a solution that contains chlorine?
Very pale green solution (often colourless)
What colour is a solution that contains bromine?
Yellow/orange solution
what colour is a solution that contains iodine?
brown solution
what is the equation for chlorine displacing bromide ions and state the colour change that occurs?
cl2(aq)+2Br-(aq) →2Cl-(aq)+Br2
colour change= pale green to orange/yellow
What is the equations when chlorine displaces iodine ions and state the colour change?
Cl2(aq)+2I-(aq) →2Cl(aq)+I2
colour change=pale green to brown
what is the equation for bromine displacing iodine ions and state the colour change?
Br2(aq)+2I-(aq)→2Br(aq)+I2(aq)
Colour change=yellow /orange to brown
What is the trend in oxidising power down group 7?
Halogens are good oxidising agents (electron acceptors)
-oxidising power decreases down the groups as their ability to attract electrons decreases down the group.
How do you test for halide ions ?
*spec:Explain why the silver nitrate solution is acidified
1- add dilute nitric acid to remove any soluble impurities that could interfere with the test(e.g. carbonates and hydroxides)
2-add silver nitrate solution to form a silver halide precipitate.
Ag+ (aq) + X– (aq) → AgX (s)
what colour precipitate does AgCl form?
chlorides produce white precipitate
Ag+(aq) + Cl-(aq) → AgCl(s)
What colour precipitate does AgF produce?
Fluorides produce no precipitate
What colour precipitate does AgBr produce?
Bromides produces a cream precipitate
Ag+(aq)+Br-(aq) → AgBr(s)
What colour precipitate does AgI produce)
iodine produces a pale yellow precipitate
Ag+(aq)+I-(aq) → AgI(s)
As AgCl and silver AgBr are similar colours how do we differentiate between them?
You add dilute ammonia and if AgCl is present it will dissolve to give a colourless solution but if AgBr is present it does not dissolve.
As AgBr and AgI are similar colours how do we differentiate between them?
You add concentrated ammonia and if AgBr is present it will dissolve to give a colourless solution but if AgI is present it will not dissolve.
What is the trend in halide ions as reducing agents?
Halide ions are good reducing agents (donates electrons).
-Reducing power increases down the group as its easier to loose electrons from larger ions due to shielding and a large atomic radius.
The reaction between chloride and concentrated sulfuric acid:
- what do you observe?
- what is the equation?
- what is the type of reaction?
NaCl(s)+H2SO4(l)→NaHSO4(s)+HCl(g)
- this is acid base reaction not a redox reaction as chloride ions are poor reducing agents and oxidation states remain unchanged
- white misty fumes of HCl are formed
The reaction between fluoride and concentrated sulfuric acid:
- what do you observe?
- what is the equation?
- what is the type of reaction?
NaF(s)+H2SO4(l)→NaHSO4(s)+HF
(g)
*this is acid base reaction not a redox reaction as fluoride ions are poor reducing agents and oxidation states remain unchanged
*white misty fumes of HF are formed
The reaction between bromide and concentrated sulfuric acid:
- what do we observe?
- what is the equation?
- what is the type of reaction?
1- In the first step we have a acid base reaction
NaBr(s)+H2SO(l)→NaHSO4(s)+HBr(g)
*white steamy fumes of HBr are evolved
2-Bromide ions are stronger reducing agents than chloride so they reduce sulfuric acid into sulfur dioxide in a redox reaction
ox= 2Br- → Br2+2e-
red=H2SO4+2e- + 2H+→SO2+H20
redox=2HBr(aq)+H2SO4(l)→Br2(g)+SO2(g)+2H2O(l)
* orange fumes and sulfur dioxide(a colouless chocking gas) are formed
The reaction between iodide and concentrated sulfuric acid:
- what do we observe?
- what is the equation?
- what is the type of reaction?
1- in the first step we have a acid base reaction
NaI(s)+H2SO4(l)→NaHSO4(s)+HI(g)
*White steamy fumes of Hi are evolved
2-iodine ions are the strongest halide reducing agents so it reduces the sulfuric acid into sulfur,sulfur dioxide, hydrogen sulfide:
ox=2I-→I2+2e- (same for all 3)
redox=2HI (aq) + H2SO4 (l) → I2 (g) + SO2 (g) + 2H2O (g)
*so2 forms a colourless acidic chocking gas & black solid
redox= 6HI (g) + H2SO4 (g) → 3I2 (s) + S (s) + 4H2O (l)
*s forms a yellow solid&black solid
redox=8HI (aq) + H2SO4 (l) → 4I2 (s) + H2S (g) + 4H2O (l)
*a colourless gas which smells of bad egg &black solid
what is a disproportionation reaction?
In a disproportionation reaction, the same element is both oxidised and reduced
What reaction occurs with chlorine and water and what is chlorine used for?
*what happens if universal indicator is added to this reaction?
Cl2(g) + H2O (l) ⇌ HClO (aq) + HCl (aq)
*It’s a disproportionation reaction
*Chlorine is used in water treatment to kill bacteria. It has been used to treat drinking water and the water in swimming pools. The benefits to health of water treatment by chlorine outweigh its toxic effects.
*If some universal indicator is added to the solution it will
first turn red due to the acidity of both reaction products. It
will then turn colourless as the HClO bleaches the colour.
Reaction of chlorine and water in sunlight:
- what is the equation?
- whats are the observations?
2Cl2 (g) + 2H2O (l)→ 4HCl (aq) + O2 (g)
*The greenish colour of chlorine water fades as the Cl2 reacts and a colourless gas (O2) is produced.
Reaction of chlorine with cold dilute NaOH solution:
- equation?
- use of products formed?
Cl2 (g) + 2NaOH (aq) →NaCl (aq) + NaClO (aq) + H2O (l)
*The mixture of NaCl and NaClO is used as bleach and to disinfect/ kill bacteria
advantages and disadvantages of chlorination of water:
*spec-Appreciate that society assesses the advantages and disadvantages when deciding if chemicals should be added to water supplies
advantages- sanitizes water,prevents spread of further infection and waterborne disease ,some chlorine remains in the system to prevent reinfection down supply
disadvantages- waters chlorinated before customers direct consent, Chlorine could react with organic matter and may form chlorinated hydrocarbons which are thought to cause cancer,Chlorine gas irritates the respiratory system and liquid chlorine causes severe chemical burns
what is the trend in atomic radii?
down a group atomic radii increases as the shielding increases
What are the trends in reactivity down group 7?
*halogens react by attracting an electron to gain a full outer shell
reactivity decreases as :
- atomic radius increases
-shielding increases
The ability of the atom to attract an electron to gain a full outer shell decreases, so the reactivity decreases
practical- what is the test for ammonium ions ?
- Add sodium hydroxide to the sample and warm the mixture
NH4+ (aq) + OH– (aq) → NH3 (g) + H2O (l) - Then, test the gas evolved with damp red litmus paper. If the sample contains ammonium ions, the red litmus paper will turn blue because the ammonia gas is alkaline
practical-how do you test for the presence of sulphate ions in a sample?
- Acidify the sample with hydrochloric acid to remove any carbonate ions that could interfere with the test
- Then, add barium chloride solution to the sample. If the sample contains sulphate ions, a white precipitate is observed – barium sulphate is insoluble so precipitates out of the solution
Ba2+ (aq) + SO42– (aq) → BaSO4 (s)
pactical- how do you test for the presence of carbonate ions in a sample?
- Add an aqueousacid to the sample. If carbon dioxide gas forms, then the sample contains carbonate ions
CO32– (s) + 2H+ (aq) → CO2 (g) + H2O (l) - Then, test the gas evolved by bubbling it through limewater. If the gas formed in the previous step is carbon dioxide, the limewater will turn cloudy due to the formation of the white precipitate calcium carbonate CO2(g) + Ca(OH)2 (aq) → CaCO3 (s) + H2O (l)
how to test for OH- ?
you can use a red litmus paper which turns blue
or
a universal indicator which turns blue/purple
what is the appearance of bromine?
red liquid, that gives off dense brown/orange poisonous fumes
what is the appearance of iodine ?
a black solid
