Topic 4 (Group 7) - Inorganic Chemistry and the Periodic Table Flashcards
What are the group 7 elements on the periodic table called?
the halogens
Describe the trend in atomic radii down group 7 elements
The atomic radius increases due to additional filled inner shells
Describe the trend in electronegativity down the group 7 elements
- The atomic radius increases
- The strength of shielding increases
- Electrons are less strongly attracted to the nucleus
- Electronegativity decreases
What is the definition of electronegativity?
The measure of the tendency of an atom to attract a bonding pair of electrons
Describe the trend in reactivity down the group 7 elements
Reactivity decreases
- Halogens need to gain an electron in order to have a full outer shell
- As you go down the group the effective nuclear charge decreases as shielding increases
- Less attraction between the nucleus and an electron
Describe the trend in boiling points down the group 7 elements
Boiling/ Melting Point increases as you go down the group
- the number of electrons per molecule increases
- the strength of the London Forces increases
- more energy is required to overcome them
What structure do halogen molecules have?
Simple molecular
What does is chlorines’ state and appearance at RTP?
yellow/green gas
What is bromines’ state and appearance at RTP?
dark red liquid
What is iodines’ state and appearance at RTP?
dark grey solid
What is astatines’ state and appearance at RTP?
black solid
What is the definition of a redox reaction?
One where both oxidation and reduction occur in the same reaction
What is the reaction that shows the trend in reactivity of Halogens?
Displacement reaction
What is the colour of Chloride ions in solution?
yellow
What is the colour of Bromide ions in solution?
orange
What is the colour of Iodide ions in solution?
brown
What are Displacement reactions of Halogens normally carried out in?
An organic solvent such as cyclohexane
Why are displacement reactions of halogens carried out in cyclohexane?
As this makes the colours easier to distinguish
Write the full equation + ionic equation and describe what happens when sodium chloride is put in a solution of bromine
NO REACTION - Bromine is less reactive than chlorine therefore the solution sustains orange
Write the full equation + ionic equation and describe what happens when sodium bromide is put in a solution of chlorine
REACTION - Chlorine is more reactive than bromine therefore, a displacement reaction occurs and the solution turns orange (from yellow)
2NaBr(aq) + Cl2 (aq) -> 2NaCl (aq) + Br2 (aq)
2Br(-) (aq) + Cl2 (aq) -> 2Cl(-) (aq) + Br2 (aq)
Write the full equation + ionic equation and describe what happens when sodium iodide is put in a solution of chlorine
REACTION - Chlorine is more reactive than iodine therefore, a displacement reaction occurs and the solution turns brown (from yellow)
2NaI(aq) + Cl2 (aq) -> 2NaCl (aq) + I2 (aq)
2I(-) (aq) + Cl2 (aq) -> 2Cl(-) (aq) + I2 (aq)
Write the full equation + ionic equation and describe what happens when sodium iodide is put in a solution of bromine
REACTION - Bromine is more reactive than iodine therefore, a displacement reaction occurs and the solution turns brown (from orange)
2NaI(aq) + Br2 (aq) -> 2NaBr (aq) + I2 (aq)
2I(-) (aq) + Br2 (aq) -> 2Br(-) (aq) + I2 (aq)
What is the colour change when cyclohexane is added to a solution containing bromide ions?
orange -> stronger orange
What is the colour change when cyclohexane is added to a solution containing Iodide ions?
brown -> pink
What do halogens act as when being reacted with group 1 and 2 metals?
oxidising agents (they themselves are reduced)
Write an example equation of the reaction of fluorine with lithium? What are the oxidation states of each of the species?
2Li (s) + F2 (g) -> 2LiF (s)
Li:
0 -> +1
F2:
0 -> -1
(Fluorine atoms are reduced to fluoride ions)
What are Halide ions good at?
Being reducing agents
Why are halide ions good reducing agents?
As they are able to donate electrons to the species being reduced
How does the reducing power of halide ions change as you descend the group? Why?
The reducing power increases. This is because the valence electron is less attracted to the nucleus as it is further away from the and there is increased shielding.
How would you test for halide ions present in solution?
- If you have a solid when testing for the presence of halide ions you must first dissolve the solid in water
- Add nitric acid to remove any carbonate impurities that could produce a false positive
- Add silver nitrate solution
- A coloured ppt. will form depending on the halide ion present in the compound
What are the coloured ppt. formed for each of the halides?
Chloride ions (Silver Chloride) - white ppt.
Bromide ions (Silver Bromide) - cream ppt.
Iodide ions (Silver Iodide) - yellow ppt.
Write a full equation and an ionic equation to show a positive result in a test for halides e.g using NaCl
AgNO3 (aq) + NaCl (aq) -> AgCl (s) + NaNO3 (aq)
Why doesn’t the halide test work for fluorine?
As silver fluoride is soluble, no ppt. formed
Why do you have to do a further test on halides after adding silver nitrate?
As the colour of the ppt.’s can be hard to observe
What is the second part of the test for halides?
Adding dilute and then conc. ammonia to the solutions
Which silver halides dissolve in dilute ammonia?
Silver Chloride
Which silver halides dissolve in conc. ammonia?
Silver Bromide and Silver Chloride
Which silver halides wont dissolve in either dilute or conc. ammonia?
Silver Iodide
What reaction shows the trend in the reducing ability of halides?
group 1 halide + sulphuric acid (H2SO4)
What is sulphuric acid?
A strong oxidising agent
Why do we use conc. sulphuric acid when testing for the trend in the reducing ability of halides?
As it is a compound that can be reduced by different amounts depending on the strength of the reducing agent
Write the equation for the reaction of NaCl with conc. H2SO4
NaCl + H2SO4 -> HCl + NaHSO4
What are the observations in the reaction of NaCl with
conc. H2SO4, including further tests with damp blue litmus, ammonia gas and acidified potassium dichromate?
OBSERVATIONS
HCl gas - Steamy fumes
FURTHER TESTS
Potassium dichromate - remains orange (has not been reduced)
Damp blue litmus - turns red as HCl gas produced
Ammonia - HCl + NH3 -> NH4Cl which produces a white smoke
What are the oxidation states of the species in the reaction of NaCl with conc. H2SO4?
Not a redox reaction, no change in oxidation states
Sulphur = +6 before and after
How do you know that HCl has not been oxidised to chlorine in the reaction of NaCl with H2SO4?
As damp blue litmus paper is not bleached
Write the equations for the reaction of NaBr with conc. H2SO4
NaBr + H2SO4 -> HBr + NaHSO4
sulphur is reduced further
2HBr + H2SO4 -> Br2 + SO2 + 2H2O
What are the observations in the reaction of NaBr with
conc. H2SO4, including further tests with damp blue litmus, ammonia gas and acidified potassium dichromate?
OBSERVATIONS
HBr gas - Steamy fumes
Br2 gas - Orange gas
FURTHER TESTS
Potassium Dichromate - turns from orange to green/blue as is reduced
Damp blue litmus - turns red as HBr gas produced
Ammonia - HBr + NH3 -> NH4Br which produces a white smoke
What are the oxidation states of the species in the reaction of NaBr with conc. H2SO4?
2nd Reaction
Sulphur:
+6 -> +4
Bromine:
-1 -> 0
Write the equations for the reaction of NaI with conc. H2SO4
H2SO4 + NaI -> HI + NaHSO4
small intermediate step
2HI + H2SO4 -> I2 + SO2 + 2H2O
final step
6HI + SO2 -> H2S + 3I2 + 2H2O
What are the observations in the reaction of NaI with
conc. H2SO4, including further tests with damp blue litmus, ammonia gas and acidified potassium dichromate?
OBSERVATIONS
HI gas - steamy fumes
H2S - smell of rotten eggs
I2 gas - purple vapour
I2 solid - purple/black solid neck deposit
FURTHER TESTS
Potassium dichromate - Sustains orange as no SO2 produced
Damp blue litmus paper - not making any acidic product as no HI gas
Ammonia - no white smoke produced as no HI gas left
What are the oxidation states of the species in the reaction of NaI with conc. H2SO4?
First reaction
no oxidation state changes
Second reaction
+6 -> +4
Third Reaction (some sulphur deposits)
+4 -> 0
Final Reaction
0 -> -2
What is the definition of a disproportionation reaction?
When the same species is both reduced and oxidised in one reaction
What are the 2 day to day uses of Chlorine?
- As a disinfectant in water to make it suitable for drinking
- As a primary element of bleach
Write the equation for chlorine when it is used as a disinfectant
Cl2 (aq) + H2O (l) -> HCl + HClO
What are the names and oxidation states of the ions for the reaction when chlorine is used as a disinfectant
Cl2 - 0
Cl in HCl - -1
Cl in HClO - +1
NB: ClO- is a chlorate (I) ion
Write the equation of how bromine reacts with water
Br2 (aq) + H2O (l) -> HBr + HBrO
Write the disproportionation equation to produce an ingredient of bleach
Cl2(aq) + NaOH(aq) -> NaCl(aq) + NaClO(aq) + H2O(l)
What are the conditions for the reaction with the equation: Cl2(aq) + NaOH(aq) -> NaCl(aq) + NaClO(aq) + H2O(l)
cold (room temperature) alkaline
What is the ionic equation for the reaction of chlorine with cold aqueous alkali and the oxidation states of chlorine in each of its species?
Cl2 + 2OH- -> Cl- + ClO- + H2O
Cl2- 0
Cl- -1
ClO- - +1
Write the disproportionation reaction equation for when chlorine reacts with hot, concentrated NaOH
3Cl2(aq) + 6NaOH(aq) -> 5NaCl(aq) + NaClO3(aq) + 3H2O(l)
Write the ionic equation for when chlorine reacts with hot, concentrated NaOH and the oxidation states of chlorine in each of its species
3Cl2 + 6OH- -> 5Cl- + ClO3- + 3H2O
Will BrO- and IO- disproportionate at lower or higher temperatures than ClO-
lower temperatures as they are less stable
What do hydrogen halides act as in solution?
strong acids
Write the equation for the reaction of a hydrogen halide with ammonia
HCl + NH3 -> NH4Cl
HBr + NH3 -> NH4Br
HI + NH3 -> NH4I
Write the equation for the reaction of a hydrogen halide with water
HCl + H2O -> Cl- + H3O+
HBr + H2O -> Br- + H3O+
HI + H2O -> I- + H3O+
What pH is the resulting solution when hydrogen halides are reacted with water
acidic
What ions are formed when hydrogen halides are reacted with water? Why?
Hydroxonium ion
Halide ion
The hydrogen halide will dissociate full into its ions in solution. The OH- ions in the water molecule act as a base and accept the H+ ions.
What is the trend in acid like behaviour down the group of hydrogen halides? Why?
The acid behaviour increases down the group. In order to behave as an acid the molecule has to be able to dissociate and, therefore, acid behaviour is dependant on how easy it is to break the bond within the molecule. The bond enthalpy decreases down the group which is why acid behaviour increases.
What is the trend in boiling point down the group of hydrogen halides? Why?
Boiling point is high at HF, then drops to HCl and then increases down the group
HF - Hydrogen bonding, PDD forces, low LF’s
HCl -> HI whilst PDD forces are decreasing this is outweighed by the increase in the number of electrons and therefore the increase in LF’s
How do you test for the presence of sulphate ions?
- If compound you are testing is not in solution, first dissolve it in pure water
- Add HCl
- Add BaCl
- If sulphate ions are present then a white ppt. will form
Write a full general equation for the test for sulphate ions
BaCl2 + XSO4 -> BaSO4 + XCl2
Write an ionic equation for the test for sulphate ions
Ba(2+) aq + SO4(2-) aq -> BaSO4(s)
Why do we add acid before adding BaCl2 in the test for sulphate ions?
Barium carbonate is also an insoluble compound, therefore if you added BaCl2 to a solution of Na2CO3 then the insoluble white ppt. barium carbonate would form giving a false positive for the test for the sulphate ion.
The acid reacts with the carbonate ions -> salt + CO2 + H2O
2HCl + X2CO3 ->2XCl (aq) + CO2 +H2O
How do you test for the presence of carbonate or hydrogencarbonate ions?
- Add HCl to the substance containing carbonate ions
- If the substance contains CO3(2-) ions or HCO3(-) ions then CO2 gas will be produced and there will be effervescence
- To confirm that CO2 gas has been produced you would bubble the gas through limewater
What is the general equation in the test for carbonate ions?
XCO3 + 2HCl -> CO2 + H2O + XCl2
How do you test for ammonium ions?
- Add sodium hydroxide solution (NaOH) and gently warm
- If the compound contains ammonium ions then ammonia gas will be produced which you can test for as it will turn damp red litmus paper blue
Does the test for ammonium ions matter if the compound is in a solid or liquid state?
No
Write the ionic equation for the test for ammonium ions
NH4(+) (aq or s) + OH(-) (aq) -> NH3 (g) + H2O (l)
Write the equation for the test for ammonium ions with ammonium chloride
NH4Cl + NaOH -> NaCl + NH3 + H2O
