Trends in properties Flashcards
What colour are the halogens?
Fluorine - pale yellow gas
Chlorine - pale green gas
Bromine - orange liquid
Iodine - grey solid (brown in solution)
What is the trend in boiling points for halogens?
Increases as we go down the group. This is because molecules are larger with more electrons. Therefore more van der Waals forces between molecules which require more energy to break.
What is the trend in electronegativity as you go down the group?
Decreases as we go down the group. Electronegativity is the ability of an atom to attract electrons towards itself in a covalent bond. This is because the atoms get larger and the distance between the positive nucleus and negative electrons also does. Less electrostatic attraction. Furthermore, there is more shielding.
Why does chlorine displace iodine?
Reactivity in halogens decreases as you go down the group. Atoms with a smaller radius attract electrons better than a larger one because of less shielding and shorter distance between the positively charged nucleus and electron.
What is the trend in the reducing power of halide ions?
Increases down the group. This is because down the group the distance between the positive nucleus and negative electrons increases and there is more shielding. This means the electrostatic attraction is weaker so electrons are lost more readily.
What are the four main sulfur products produced in the reduction of conc sulphuric acid by a sodium halide and which one is not a reduction product?
NaHSO4, SO2, S, H2S
NaHSO4 is not a reduction product because the oxidation state of sulfur is the same as in sulphuric acid (+6). No redox reaction.
Which product do all three halides (Cl-, Br-, I-) produce with conc H2SO4 and what will you observe?
H2SO4 + NaCl –> NaHSO4 + HCL
You will observe misty white fumes being produced.
Which product do two halides (Br-, I-) produce with conc H2SO4 and what will you observe?
Sulphur dioxide. Full ionic equation (draw out two half equations in exam):
H2SO4 + 2H+ + 2Br- –> Br2 + SO2 + 2H2O
You will observe orange vapour of bromine.
Which products do I- produce with conc H2SO4 and what will you observe?
S and H2S. A yellow solid which is sulfur will be observed and a rotten egg smell from H2S. These are two separate reactions and to work them out in the exam use the half equations.
How can halide ions be identified by silver nitrate solution?
Add dilute nitric acid then add silver nitrate solution. If the white precipitate, it is Chloride. If the cream precipitate, it is Bromide. If the yellow precipitate, it is Iodide.
Why add dilute nitric acid before adding silver nitrate solution?
We add nitric acid to react with any other anions other than the halide (e.g. carbonates). This could give a false result otherwise.
What is a further test to confirm the halide after silver nitrate is added?
AgCl will dissolve in a dilute ammonia solution. AgBr will dissolve in conc ammonia solution. AgI will not dissolve in ammonia solution.
