I- Halogens =) Flashcards
State why the silver nitrate solution is acidified when testing for iodide ions. (1)
- remove any ions that would react w/ silver nitrate–> interfere w/ the test
- prevents formation of other silver ppts.
- CO3 2- / OH- ions
When concentrated sulfuric acid is added to solid potassium chloride, white solid is produced, misty white fumes turned blue litmus paper red.
1. simplest ionic equation
2. identify species responsible for misty white fumes (2)
- H2SO4 + 2Cl –> 2HCl + SO4 2-
- HCl
At room temperature and pressure, r.t.p., chlorine is a gas, bromine is a liquid and iodine is a solid.
Explain why these halogens have different physical states at r.t.p. (3)
- no. of e- ↑ down the group
- vdW
- ↑ Cl<Br<I
Suggest a disadvantage of treating drinking water by adding chlorine. (1)
- Wasteful ∵ most potable water x used for drinking - used in washing clothes etc
- Some people suffer eye irritation / unpleasant taste
- can react with organic compounds to produce harmful substances
Chlorine has a low boiling point because the forces between the molecules are weak.
Explain how these forces arise between molecules of chlorine. (3)
- random movement of e-
- induces dipole in a neighbouring molecule
- temp dipoles attract
A student completes an experiment to determine the percentage by mass of sodium chloride in a mixture of sodium chloride and sodium iodide.
Silver nitrate is added to the solution.
Suggest why an excess is used. (1)
To ensure that all the halide ions (chloride and iodide) are removed from the solution.
Write an equation for the reaction which occurs when chlorine is bubbled into water.
Identify the substance which causes the resulting solution to be pale green. (2)
- Cl2 + H2O ⇌ HClO + HCl
- CHLORINE
Adding chlorine to water in the absence of sunlight :
The pool manager maintains the water at a pH slightly greater than 7.0
Explain how this affects the equilibrium established when chlorine is added to water. (2)
- OH- ions react w/ acids
- eq. shifts to RHS
Explain why chlorine is used to kill bacteria in swimming pools, even though chlorine is toxic. (2)
- only used in small amounts
- health benefits outweigh the risks
Chlorine reacts with cold, aqueous sodium hydroxide in the manufacture of bleach.
Give an equation for this reaction. (1)
Cl2 + 2 NaOH → NaCl + NaClO + H2O
When iodide ions are oxidised using concentrated sulfuric acid, sulfur dioxide, a yellow solid and a foul-smelling gas are all formed.
Give an equation to show the reaction between iodide ions and concentrated sulfuric acid to form the yellow solid. (1)
6 I– + 6 H+ + H2SO4 → S + 3 I2 + 4 H2O
Fumes of sulfur dioxide are formed when sodium bromide reacts with concentrated sulfuric acid.
Give one other observation from this reaction. (1)
brown/ orange fumes
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. (2)
Cl2 + H2O –> HCl + HClO
- Cl2 gains e- (to form Cl-) + loses e- (to form ClO-)
A student bubbles chlorine gas through a solution od sodium iodide.
State the observation made. (1)
brown solution/ black solid
Suggest an observation used to judge when all iodine had reacted, in a reaction between iodine solution and excess of acidified butanone.
CH3CH2COCH3 + I2 → CH3CH2COCH2I + HI
(1)
goes colourless/ brown colour removed
