Module 3 - Halogens Flashcards
Explain why the electronegativity of the halogens decreases down the group. 2
- More electron shells / more shielding
- weaker attraction between nucleus and bonding pair of electrons
Concentrated sulfuric acid reacts with solid sodium chloride and with solid sodium bromide.
State one similarity in, and one difference between, these reactions. 2
Similarity: one from
undergo acid-base reaction / misty white fumes are observed/effervescence
Difference: one from
bromide undergoes a redox reaction/red-brown-orange fumes are observed with bromide/Br2 produced with bromide/SO2 produced with bromide
Give an equation for the reaction of chlorine with water to form a solution containing two acids.
Explain, with reference to electrons, why this is a redox reaction.
Cl2 + H2O → HCl + HClO
allow Cl2 + H2O → 2 H+ + Cl− + ClO−
chlorine/Cl/Cl2 gains electron(s) (to form Cl−) and loses electron(s) (to form ClO−)
Chlorine is used to treat water even though it is toxic to humans.
Give one reason why water is treated with chlorine.
Explain why chlorine is added to water even though it is toxic.
Give an equation for the reaction of chlorine with cold water. (3)
Reason: sterilise water / disinfect water / kill bacteria / kill microorganisms / kill microbes
Explanation: health benefit outweighs risk / only used in small quantities/low concentrations
Equation:
Cl2 + H2O ⇌ HCl + HClO
2 Cl2 + 2 H2O → 4 HCl + O2
Bromine (Br2), strontium chloride (SrCl2) and iodine monochloride (ICl) all have similar Mr values.
Suggest, with reasons, the order of melting points for these three substances. (6)
SrCl2> ICl > Br>
SrCl2 strong ionic bonds / (strong electrostatic attraction between opposite ions)
Lattice so many strong bonds to overcome
ICl has dipole-dipole between molecules – weaker than ionic bonds
Br2 has van der Waals forces between molecules – much weaker
Accept London / dispersion / induced dipole forces
Explain why chlorine has a lower boiling point than bromine. (2)
- has fewer electrons electron shells
It has a smaller atomic radius - strength of london foces are weaker
- fewer energy needed
Describe and explain the trend in bioling points of halogens as you go down (3)
bioling point increases
numbr of shells increases
strength of london forces increases
more energy need to overcme
explain why bromine has a lower bp tha iodine monochloride, even though they have similar
Mr (2)
permanent dipole bonds stronger than lodon forces
icl s polar, bromine is not.
explain why halogens are non polar
no permanent dipole, arent oppostely charged, exists as diatomic
Explain why chlorine is used to kill bacteria in swimming pools, even though chlorine is toxic.
Only used in small amounts
The health benefits outweigh the risks
Chlorine displaces iodine from aqueous potassium iodide.
Write the simplest ionic equation for this reaction.
Cl2 + 2I− I2 + 2Cl−
State how you could test a sample of water to show that it contains chloride ions.
Give a reagent, one observation and the simplest ionic equation for the reaction with the reagent.(3)
Silver nitrate OR AgNO3
white precipitate
Ag+ + Cl− AgCl
Explain why chloride ions are weaker reducing agents than bromide ions.
chloride ion has fewer (electron) shells/levelselectron(s) lost
from a chloride ion is more strongly held by the
nucleus compared with that lost from a bromide
ion
