Group 7, the halogens Flashcards
How does electronegativity change as you go down group 7
It decreases as you go down because the other atom gets further away from the halogens nucleus
How does melting and boiling point change as you go down group 7
They increase as you go down the group as the larger atoms have more electrons so stronger VDW forces
How does oxidising agent ability change as you go down group 7
As you go down the group, oxidising ability decreases as halogens want to gain an electron but the bigger the atom, the further from the nucleus
How do halogens react with metal halides
More reactive halogens will displace less reactive halogens e.g.
Cl2 + 2NaBr —> 2NaCl + Br2
What is the oxidising agent in this reaction
Cl2 + 2NaBr —> 2NaCl + Br2
Chlorine is the oxidising agent as it has gained an electron
How does reducing agent ability of halide ions change as you go down the group
As you go down the group, the atom becomes larger and so it is easier for it to lose an electron so reducing agent ability of halides increases down the group
What is the general equation for a sodium halides reaction with H2SO4
NaX + H2SO4 —> HX + NaHSO4
How can halide ions be identified
Add dilute nitric acid
Add silver nitrate
How can halide ions be identified
Add dilute nitric acid
Add silver nitrate
A precipitate will be formed
What will you witness if NaBr reacts with H2SO4
Steamy fumes
What will you witness if NaI reacts with H2SO4
Steamy fumes
Black solid of iodine
Small amounts of yellow sulphur
What are the equations for NaBr and H2SO4
NaBr + H2SO4 —> HBr + NaHSO4
2H+ + 2Br- + H2SO4 —> SO2 + 2H2O +Br2
What is the equation for NaI and H2SO4
NaI + H2SO4 —> HI + NaHSO4
8H+ + 8I- + H2SO4 —> H2S + 4H2O + 4I2
6H+ + 6I- + H2SO4 —> S + 4H2O + 3I2
2H+ + 2I- + H2SO4 —> SO2 + 2H2O + I2
What colour will a chloride ion produce in the halide test
White ppt
What colour will a bromide ion produce in the halide test
Cream ppt
What colour will an Iodide ion produce in the halide test
Yellow ppt
How does the solubilities of the silver halides change in ammonia
Silver chloride - dissolves in dilute ammonia
Silver bromide - dissolves in concentrated ammonia
Silver iodide - Insoluble in ammonia
What colour will an fluoride ion produce in the halide test
Nothing will happen
Why is silver nitrate used as the halide test
It is sensitive enough to detect fairly small concentrations of halide ions
Why is dilute nitric acid put into the halide test before the silver nitrate
Prevents unreacted hydroxide ions reacting with the silver ions to give a confusing precipitate
Why is ammonia used in the halide test
Colours are similar and can be difficult to distinguish between so ammonia sorts them out objectively
How does chlorine react with water in the dark
Cl2 + H2O —> HClO + HCl (these will dissociate producing chloride and chlorate ions)
How does chlorine react with water in sunlight
2Cl2 + 2H2O —> 4HCl + O2 (produces chloride ions and oxygen)
What are the advantages and disadvantages of adding chlorine to water
+
Kills bacteria
Inhibits algal growth
-
Toxic and harmful
Forms chlorinated hydrocarbons
The positives outweigh the negatives
How is chlorine used in water treatment
Swimming pools and drinking water
What is the reaction equation between chlorine and cold, dilute NaOH
Cl2 + 2NaOH —> NaClO + NaCl + H2O
What is NaClO used for
Bleach
