Group 7 The Halogens Flashcards
Colour of fluorine + state
Pale yellow
Gas
Chlorine colour + state
Pale green gas
Bromine colour and state
Brown -orange
Liquid
Iodine colour and state
Grey
Solid
Trend in boilings points group 7
Increase down the group
Increase Van Der waals due to increasing size and relative mass of atoms
Trend in electronegativity group 7
This decreases going down the group
As the atoms get larger the distance between positive nucleus and bonding electron increases + more shielding
Displacement rule in halogens
A more reactive halogen will displace a less reactive halogen
What colour is iodine solution
Brown
Standard equation of halogens displacing each other half/ ionic equation
X2 + 2Y- —> 2X- + Y2
How is bleach made which reaction
Disproportionating reaction
Equation for making bleach
2NaOH + Cl2 —> NaClO + NaCl + H2O
Uses of bleach
Cleaning agents
Treating water
Bleaching fabrics
What happens in a disproportionation reaction w chlorine
The chlorine is reduced and oxidised simultaneously
Why is chlorine added to water
To kill bacteria
Reaction when water is added to chlorine
H2O + Cl2 —> 2H+ + Cl- + ClO-
Reaction when chlorine is added to water but in sunlight ionic
2H2O + Cl2 —> 4H+ + 2Cl- + O2
Advantages of chlorinating drinking water x4
Destroys microorganisms that causes diseases
Long lasting so reduces bacteria build up
Reduces the growth of algae
Not doing it can lead to cholera epidemic
Disadvantages of chlorinating drinking water x3
Chlorine gas is toxic
Liquid chlorine causes chemical burns
Chlorine could react with organic compounds to make chloroalkanes. These can cause cancer.
Are halides oxidising or reducing agents
Reducing agents
Trend in reducing ability of halides review
Increase going down
They are reducing agents so oxides themselves so they lose electrons
Going down distance between outer electron and nucleus increases and more shielding so attraction is weaker.
Test for halide ions
1) add dilute nitric acid to remove the any ions that could give false results
2) add silver nitrate
3) further test with ammonia
Chloride ions form what colour precipitate
White
Bromine produce what coloured ions..
Cream
Iodine produce what coloured ions
Yellow
Half equation standard for halide test with silver nitrate
Ag+(aq) + X-(aq) —> AgX(s)
Cl- white precipitate with ammonia observation
Dissolves in dilute ammonia
I- yellow precipitate with ammonia observation
Insoluble in concentrated ammonia
Br- cream precipitate with ammonia observation
Insoluble in concentrated ammonia
How to test for group 2 ions
Flame test
Dip wire in hydrochloric acid
Place loop into blue flame
What colour calcium on flame test
Dark red
What colour strontium in flame test
Red
What colour barium in flame test
Green
How to test for ammonium compounds
Add sodium hydroxide
Heat gently
Positive - ammonia gas produced bleaches litmus paper blue
Test for hydroxide + problem
They are alkaline so will turn red litmus paper blue
However lots of thing turn litmus paper blue so need to do further tests
Test for carbonates
Add acid E.g. hydrochloric acid
Fizzing and Produces CO2 gas ( if positive)
Limewater turns cloudy if CO2 is present
What order to test ions + why
1) carbonates
2) sulfates
3) halides
To prevent false positives
Ionic equation for carbonate test
CO3 -2 + 2H+ —> CO2 + H2O
Nitrogen gas formula
N2
Forulma bleach
NAClO
Half equation to show oxidation of halide ion to halogen
2X- —> X2 +2e-
How to test for barium
Add any sulphate E.g. SO42-
White precipitate
Bromine is what colour solution
Yellow
Reaction when chlorine is added to water not ionic
2Cl2 + 2H2O —> 4HCl +O2
Ionic equation test for barium with…
Sulfates
Ba2+ + SO4-2 —> BaSO4
Equation when chlorine is added to drinking water
2Cl2 + 2H2O —> 4HCl +O2
Why is catalyst used in equilibrium
No effect on yield
Lowers temperature used
Lowers cost
State why not more than the minimum ionisation energy is used to ionise a sample
To prevent further ionisation
Explain why sodium oxide forms alkali solution when reacts with water
Contains O2- ions
React with water to form OH- ions
O2- + H2O —> 2OH-
Metal oxide + hydroxide
Metal oxide ion + water
Why is second ionisation energy higher than first ionisation energy
More energy to remove an electron from a more positive ion
Which element in period 2 has the highest 2nd ionisation energy
Li
Chlorine + aqueous sodium hydroxide cold dilute
2NaOH + Cl2 —> NaCl + NaOCl + H2O
Ionic equation w state symbols of metal reacting with water group 2
X (s) + 2H2O(l) —> X+2(aq) + 2OH- (aq) +H2(g)
Practical steps to determine solubility of solution
Take a known volume of saturated solution
Evaporate to filtrate dryness
Weigh the residue
Equation metal hydroxide + sulfuric acid
X(OH)2 + H2SO4 —> XSO4 + 2H2O
Reactivity with water down group 2
Increases
Why should you not add water to burning magnesium
Forms hydrogen
Which is flammable
Strontium chloride + sodium sulfate
Sodium chloride + strontium sulfate
How to test for presence of bromide ions w ammonia
Add nitric acid then silver nitrate
Then add dilute ammonia
Cream precipitation forms
No visible change
Why does calcium have higher melting point than strontium
Delocalised electrons are closer to positive nucleus because atomic radius is smaller
This means stronger metallic bonding
Equation chlorine redissolving in ammonia
AgCl(s) + 2NH3 (aq) —> Ag(NH3)2 + (aq) + Cl-
Why is chlorine added to water even though it is toxic
Not harmful in low concentration
Sulfur if acid formula
H2SO4
Which halide ion with sulphuric acid is not a redox equasion
Chlorine + fluorine
In the tests for halides why is excess silver nitrate used
To ensure ALL the halide ions precipitate out
Reaction sodium halide and sulfuric acid + what do you see
H2SO4 + NaX —> NaHSO4 + HX
Misty fumes
Reaction concentrated sulphuric acid with fluorine and chlorine + why
No reaction
Sulfuric acid is not a strong enough oxidising agent to oxides chloride or fluoride ions.
Bromide and concentrated sulfuric acid + which oxidised and reduced + what observation
2Br- —> Br2 + 2e- (oxidised)
H2SO4 + 2H+ + 2e- —> SO2 + 2H2O (reduced)
Combine for overall equations
Orange vapour
Iodine ions with concentrated sulfuric acid
1) NaI + H2SO4 —> NaHSO4 + HI
2) 2H+ + 2I - + H2SO4 —> I2 + SO2 + 2H2O
3) 6HI + SO2 —> H2S + 3I2 + 2H2O
Role of chloride ions in NaCl + H2SO4 —> NaHSO4 + HCl
Base
Bromine colour in solution
Orange
Iodine colour in solution
Brown
As you move from HCl to HI
The bond dissociation energy…
The bond polarity …..
Decreases
Decreases
As you move from HCl to HI they are more/less easily oxidised in aqueous solutions
More
Role of chlorine in NaCl + H2SO4 —> NaHSO4 + HCl
Proton donor
Colour magnesium hydroxide
White
What colour are the hydroxides of group 2
WHITE ALL
