Halogens Flashcards
How does fluorine exists naturally? - state and colour
A pale yellow gas
How does chlorine exist naturally - colour and state
Pale green gas
How does bromine exist naturally - state and colour
(Brown) Orange liquid
How does iodine exist naturally - state and colour
Grey solid
Colour of AgCl precipitate
white
Colour of AgBr precipitate
cream
Colour of AgI precipitate
Yellow
Which of the silver halide precipitates dissolve in dilute ammonia
AgCl ONLY
Which of the silver halide precipitates dissolves in excess ammonia
AgCl
AgBr
Which of the silver halide precipitate doesn’t dissolve in ammonia
AgI
What is the trend in reducing power down the halogens
-increase in reducing power
-as they’re oxidised (lose e-) more easily down the group —> ionisation energies increase down group due to increase shielding outweighing increase in nuclear charge
How does reactivity change down the halogen group?
- Decreases
-Halogens want to gain 1e- to have stable noble gas configuration
-down group atomic radius and shielding increases, outweighing increase in nuclear charge
-so electrons are attracted less strongly
How does oxidising power change down the group?
- Decreases
- halogens are reduced (gain electron) less easily due to increase in atomic radius, shielding which outweigh increase in nuclear charge
How do we measure a halogens reducing power?
-By reacting halide salt with concentrated sulfuric acid and observing whether a further reaction occurs
Describe the describe between KCl and conc H2SO4, give the reaction and state conclusions we make
KCl (s) + H2SO4 (aq) —> KHSO4(s) + Hcl (g)
White steamy fumes of HCl observed
No further reaction occurs , HCl doesn’t react further with H2SO4
Acid-base NOT redox reaction, so Cl must not be a very good reducing agent
Describe the reaction between KBr and H2SO4, state any further reactions and observations
- KBr + H2SO4 —> KHSO4 + HBr
(HBr reacts further—> better reducing agent that chlorine) - 2HBr + H2SO4 —> SO2 + Br2 + 2H2O
(REDOX reaction —> bromine oxidised and sulfur is reduced )
Firstly white steamy fumes are given off
Then in the second reaction the solution will either turn orange (due to bromine), or you’ll see red/orange fumes or bromine gas
Describe the reaction between KI and H2SO4, state any further reactions and observations
- KI + H2SO4 —> KHSO4 + HI Acid/base
(HI reacts further with H2SO4–> good reusing agent ) - 8HI + H2SO4 —> H2S + 4I2(s) + 4H2O
(REDOX)
Observations :
1.White steamy fumes of HI given off
2 . Black solid of iodine form, or purple iodine gas is seen, H2S has a bad egg smell
Give quantitative evidence for the difference in reducing strengths of the halogens
• Chlorine is unable to change the oxidation state of sulfur in H2SO4
•Bromine is able to reduce sulfur to the extent that it’s oxidation state goes from +6 in H2SO4 to +4 in SO2
•Iodine is able to reduce sulfur to the extent that it’s oxidation state goes from +6 in H2SO4 to -2 H2S (LARGE CHANGE)
Therefore reducing power increases down group, and out of Cl Br and I, iodine is best reducing agent
How do we test for the difference in oxidising strength of the halogens?
-By adding a halide salt to a solution of liquid halogen
-more reactive halogens (the better oxidising agents), displace the halide in the salt, causing a colour change
Why do we add an organic solvent - such as hexane- to the solution of the halide salt and halogen
- It allows us to see the colour change more clearly, as halogens are non-polar, so dissolve better in organic solvents and can be seen more clearly
State the colours of iodine, chlorine and bromine in an organic solvent
Chlorine - pale Green
Bromine - orange
Iodine - purple
Why are solvents important it comes to halogens?
- Halogens appear different colours in different solvents
State the colours of chlorine iodine and bromine in an aqueous solvent
Chlorine - colourless
Bromine - yellow
Iodine - brown
What is the important thing to remember about halogen displacement reactions?
-Halogens displace all Halogens BENEATH them in the group
- as reactivity decreases down group, so most reactive halogens are at the top (best oxidising agents at the top)
Write the equation for the reaction between chlorine and cold dilute NaOH
2NaOH + Cl2 —> NaCl + NaClO + H2O
-This process is used industrially to produce bleach - NaClO
Write the equation for the reaction between chlorine and hot concentrated NaOH
6NaOH + 3Cl2 —> 5NaCl + NaClO3 + 3H2O
Give the full equation for the reaction between KCl and H2SO4, and state the reaction type
KCl + H2SO4 —> HCl + KHSO4
-acid base reaction
Give the full equation for the reaction between KBr and H2SO4, and state the reaction type
2NaBr + 3 H2SO4 —> NaHSO4 + SO2 + Br2 + 2H2O
-Redox reaction
-Orange fumes of Br2 given off
