3.2.3- Group 7(17), the halogens (PAPER 1) Flashcards
What is the trend in atomic radius down Group 7?
Atomic radius increases due to combined effect of an increase in number of shells and shielding being greater than increase in + charge.
What is the trend in electronegativity down Group 7?
Electronegativity decreases down the group as atomic radius and shielding increases (added electron shells) so bonding pair of electrons in the covalent bond are further from the positively charged nucleus.
Less electrostatic attraction between nucleus and bonding pair of electrons.
What is the trend in melting/boiling point down Group 7?
Melting+ boiling points increase as the number of electrons in each molecule is increasing, increasing the number/ strength of van der waal’s forces between the moleucles, it is harder to separate one molecule from another.
What is the trend in ionisation energy down Group 7?
Ionisation energy decreases as there is more shielding and atoms get bigger, so weaker attraction between nucleus and electron in outer shell.
How do halogens act as oxidising agents + general equation.
Halogen molecules react by gaining electrons from other substances.
X2 + 2e- ——> 2X-
Halogen molecule has been reduced as it has gained electrons, it has oxidised the other substance.
How is oxidising ability of halogens shown in reaction between sodium and chlorine?
2Na (s) + Cl2 (g) —- 2NaCl (s)
Chlorine oxidises the sodium from state 0 to +1
Chlorine is reduced from 0 to -1
What is the trend in oxidising ability of halogens down Group 7?
Oxidising power of halogens decreases down group 7.
AND
Ability of a halogen molecule to be reduced decreases.
Number of energy levels increases, atomic radius increases, shielding increases between outer shell electrons and nucleus so larger atoms attract extra electron less strongly.
What occurs in halogen-halide displacement reactions?
Redox reaction occurs when more reactive halogen nearer the top displaces a less reactive halide ion from its aqueous compound and oxidises it.
What occurs when chlorine water is added to potassium chloride solution?
No reaction as they are just as reactive.
COLOURLESS/ PALE GREEN (CL2)
What occurs when chlorine water is added to potassium bromide solution?
Chlorine is more reactive than a bromide ion so displaces it.
ORANGE/YELLOW SOLUTION (BR2) MADE
Cl2+ 2Br—-> 2Cl- + Br2
What occurs when chlorine water is added to potassium iodide solution?
Chlorine is more reactive than an iodide ion so displaces it.
BROWN SOLUTION (I2) MADE
Cl2 + 2I- —–> 2Cl- + I2
What occurs when bromine water added to potassium chloride solution?
No reaction as bromine is less reactive than chloride ions.
ORANGE/YELLOW SOLUTION (BR2) MADE
What occurs when bromine water added to potassium bromide solution?
No reaction as bromide ions and bromine are just as reactive.
ORANGE/YELLOW SOLUTION (BR2) MADE
What occurs when bromine water added to potassium iodide solution?
Bromine is more reactive than an iodide ion so displaces it.
BROWN SOLUTION (I2) MADE
Br2 + 2I- —–> 2Br- + I2
What occurs when iodine solution added to potassium chloride solution?
No reaction as iodine less reactive than chloride ions.
BROWN
What occurs when iodine solution added to potassium bromide solution?
No reaction as iodine less reactive than bromide ions.
BROWN
What occurs when iodine solution added to potassium iodide solution?
No reaction as iodine just as reactive as iodide ions.
BROWN
What is the order of oxidising power of halogens?
F2 > Cl2 > Br2 > I2
What occurs when Cl2 is bubbled through solution containing NaBr?
Overall equation and 2 half equations.
Cl2(aq) + 2NaBr (g) —-> 2NaCl (aq)+ Br2(aq)
Chlorine oxidises the bromide ions to aqueous bromine- Br2.
2Br- —-> Br2 + 2e- (redOX= OXIDATION electrons on right)
Cl2 + 2e- —-> 2Cl- (REDox = REDUCTION electrons on left)
What is the trend in reducing ability of the halide ions?
Reducing ability of halides increases down the group as there are more electron energy levels, the shielding between outer electrons and nucleus increases so so there is a lower electrostatic attraction between nucleus and electrons.
It is easier to remove an electron from a halide ion down the group, they are more readily oxidised/ powerful reducing agents
How to make hydrogen chloride using a halide salt and concentrated sulfuric acid (1 STEP)?
Concentrated sulfuric acid donates hydrogen ion to a chloride ion to make hydrogen chloride.
NaCl + H2SO4 ——> HCl + NaHSO4
white steamy fumes HCl
What effect does the addition of H2SO4 to NaCl have on potassium dichromate paper and lead ethanoate paper?
No effect on either
What effect does the addition of H2SO4 to NaBr have on potassium dichromate paper and lead ethanoate paper?
potassium dichromate paper turns green in the presence of SO2
lead ethanoate paper has no reaction
What effect does the addition of H2SO4 to NaI have on potassium dichromate paper and lead ethanoate paper?
potassium dichromate paper turns green in the presence of SO2
lead ethanoate paper turns black in the presence of H2S
How to make hydrogen fluoride using a halide salt and concentrated sulfuric acid (1 STEP)?
Concentrated sulfuric acid donates hydrogen ion to a fluoride ion to make hydrogen fluoride.
NaF + H2SO4 ——-> HF + NaHSO4
white steamy fumes HF
Why do only acid-base reactions occur when using fluoride or chloride ions?
The H2SO4 is not strong enough an oxidising reagent to oxidise the chloride and fluoride ions so redox reactions occur.
How to use bromide ions with concentrated sulfuric acid (2 STEPS)?
Br- ions are stronger reducing agents than Cl- and F- and after the initial acid- base reaction reduce the sulfur in H2SO4
from +6 to + 4 in SO2
Initial step the same: NaBr + H2SO4 —–> HBr + NaHSO4
-(H2SO4 acts as acid)
2nd redox step: 2HBr + H2SO4 —-> Br2
+ SO2 + 2H2O
-(H2SO4 acts as oxidising agent, the S is reduced from +6 to +4)
What are the half equations for reaction of bromide ions with concentrated sulfuric acid?
+ Overall ionic
redOX 2Br—–> Br2 + 2e-
REdox H2SO4 + 2 H+ + 2 e- —-> SO2 + 2 H2O
overall ionic= H2SO4 + 2H+ + 2Br —-> Br2 + SO2 + 2H2O
oxidation of Br-, reduction of H2SO4
What are the observations for reaction of bromide ions with concentrated sulfuric acid?
White steamy fumes of HBr
orange/ red fumes of Bromine, and a colourless, acidic gas SO2
How to use iodide ions with concentrated sulfuric acid ( 2 STEPS) and what are observations?
I- ions are the strongest halide reducing agents. They can reduce the sulfur from
+6 in H2SO4 to + 4 in SO2, to 0 in S and -2 in H2S.
observations= white steamy fumes HI, purple flames I2, colourless acidic gas SO2, yellow solid S, eggy gas H2S
Initial step the same: NaI(s) + H2SO4
(l) —-> NaHSO4 (s) + HI(g)
What is the equation for the reduction of sulfur from +6 in H2SO4 to +4 in SO2 using iodide ions?
AND 2 HALF EQUATIONS
2HI + H2SO4 —-> I2 + SO2 + 2H2O
redOX (e- on right)
2I- —-> I2 + 2e-
REdox (e- on left)
H2SO4 + 2 H+ + 2 e- —-> SO2 + 2 H2O
What is the equation for the reduction of sulfur from +6 in H2SO4 to 0 in S using iodide ions?
AND 2 HALF EQUATIONS
6HI + H2SO4 —-> 3 I2 + S + 4 H2O
redOX (e- on right)
2I- —–> I2 + 2e-
REdox (e- on left)
H2SO4 + 6H+ + 6e- —–> S + 4H20
What is the equation for the reduction of sulfur from +6 in H2SO4 to -2 in H2S using iodide ions?
AND 2 HALF EQUATIONS
8HI + H2SO4 ——> 4I2 + H2S + 4H2O
redOX (e- on right)
2I- —–> I2 + 2e-
REdox (e- on left)
H2SO4 + 8H+ + 8e- ——-> H2S + 4H20
What are the steps for testing for halides using silver nitrate and ammonia?
1) Add dilute nitric acid (HNO3) to the solution in order to react with carbonates present to prevent formation of precipitate Ag2CO3.
2) Add silver nitrate solution (AgNO3) producing a precipitate for Cl-, Br- and I- ions.
3) Add dilute and concentrated ammonia to see if precipitates re-dissolve.
What is a positive result for chloride ions?
white precipitate
Ag+ (aq) + Cl- (aq) —> AgCl(s)
What is a positive result for bromide ions?
cream precipitate
Ag+ (aq) + Br- (aq) —-> AgBr (s)
What is a positive result for iodide ions?
pale yellow precipitate
Ag+ (aq) + I- (aq) —-> AgI (s)
What occurs when ammonia is added to the 3 halides?
AgCl- white precipitate dissolves in dilute NH3
AgBr- cream precipitate dissolves in concentrated NH3
AgI- yellow precipitate insoluble in NH3
What is the trend in solubility of the silver halides in ammonia?
Decreases in the order: AgF > AgCl > AgBr > AgI
How does chlorine react with cold water?
To produce chlorate (I) ions ClO- and chloride ions.
Cl2 + H20 —-> HCl + HClO
chloric acid can further dissociate in water to form….
Cl2 + H20 —-> ClO- + Cl- + 2H+
Chlorine oxidised from 0 in Cl2 to -1 in Cl-. Chlorine reduced from 0 in Cl2 to +1 in ClO-
What can chloric acid (HClO) or chlorate ions (ClO-) be used for?
Sterilising water by killing bacteria.
What is the reaction of chlorine in sunlight/UV?
Chlorine rapidly lost from pool water.
No ClO- made
Cl2 + 2H2O —–> 4H+ + 2Cl- + O2
What are the benefits and limitations of using chlorine to sterilise water?
Benefits: destroys microorganisms that cause disease, long lasting reducing bacteria build up, reduces growth of algae that discolours water.
Limitations: chlorine gas is toxic and irritates respiratory system, liquid chlorine causes chemical burns, chlorine can react with organic compounds in the water forming chloroalkanes.
How does chlorine react with cold, dilute, sodium hydroxide?
Cl₂ (aq) + 2NaOH(aq) → NaOCl(aq) + NaCl(aq) + H₂O(l)
chlorine is oxidised and reduced in a process known as disproportionation, forming sodium hypochlorite (NaOCl) and sodium chloride (NaCl).
How does chlorine react with solid sodium chlorate?
NaClO + H2O ⇌ Na+ + OH- + HClO
sodium dissolves in water to form chloric (I) acid.
swimming pools need to be kept slightly acidic as otherwise equilibrium moves to left and HClO removed as ClO- ions.
How is bleach made? + reaction
By a disproportionation reaction where chlorine has been reduced and oxidised.
Cl= 0, +1, -1
2NaOH (aq) + Cl2 (g) —–> NaClO (aq) + NaCl (aq) + H2O (l)
chlorine and sodium hydroxide form sodium chlorate (I) solution.
