Halide ions Flashcards
How do group 7 elements form ions?
They gain one electron to form a full outer shell
What is the reducing power of halides?
How easy it is for a halide ion to lose an electron depends on the attraction between the nucleus and the outer electrons
What is the trend in reducing power of halides as you move down the group?
Increases
What happens to the halide ions when they take part in a redox reaction?
It reduces something and is oxidised itself
What do all halides react with to produce?
Concentrated sulphuric acid to give a hydrogen halide
What is the general equation for a halide reacting with concentrated sulphuric acid?
NaX + H2SO4 _> NaHSO4 + HX
What is the reaction of strong halides with concentrated sulfuric acid? What are the products?
2HX + H2SO4 + X2 + SO2 + 2H2O
Reduce the sulphuric acid to water and sulfur dioxide
What are the 2 half equations for the reaction of strong halides with concentrated sulphuric acid?
2X- -> X2 + 2e-
H2SO4 + 2H+ + 2e- -> SO2 + 2H2O
What can iodine reduce SO2 to and why?
H2S or S
It is such a strong reducing agent
What is the equation for the reaction between NaF and H2SO4?
NaF + H2SO4 -> NaHSO4 + HF
What is the equation for the reaction between NaCl and H2SO4?
NaCl + H2SO4 -> NaHSO4 + HCl
What observation can be made from the reactions of NaF and NaCl reacting with concentrated sulphuric acid?
Misty fumes from either HF or HCl
What are the equations for the two reactions of NaBr with H2SO4?
NaBr + H2SO4 -> NaHSO4 + HBr
2HBr + H2SO4 -> Br2 + SO2 + 2H2O
Why are there two reactions for NaBr and H2SO4?
HBr is a stronger reducing agent than HCl and then reacts with the H2SO4 in a redox reaction
What observations can be made from the first reaction of NaBr reacting with concentrated sulphuric acid?
Misty fumes of HBr
What observations can be made from the second reaction of NaBr reacting with concentrated sulphuric acid?
Choking fumes of SO2
Orange fumes of Br2
How many reactions are there when NaI reacts with concentrated sulfuric acid?
3
What is the equation for the first reaction when NaI reacts with concentrated sulfuric acid?
NaI + H2SO4 -> NaHSO4 + HI
What is the equation for the second reaction when NaI reacts with concentrated sulfuric acid?
2HI + H2SO4 -> I2 + SO2 + 2H2O
What is the equation for the third reaction when NaI reacts with concentrated sulphuric acid?
6HI + SO2 -> H2S + 3I2 + 2H2O
What observations can be made for the third reaction of NaI reacting with concentrated sulfuric acid?
Fumes of H2S
Solid iodine
How do you test for halides?
1) add dilute nitric acid to remove ions which might interfere
2) add a few drops of silver nitrate solution
What is the general equation for the reaction of halides with silver nitrate solution?
Ag+ + X- -> AgX
What colour precipitate does chloride ions produce?
White
What colour precipitate does bromide ions produce?
cream
What colour precipitate does iodide ions produce?
Yellow
What reaction occurs when dilute NH3 is added to chloride ions?
Dissolves
What reaction occurs when concentrated NH3 is added to bromide ions?
Dissolves
What reaction occurs when concentrated NH3 is added to iodide ions?
No reaction
Insoluble
