Group 7 Flashcards
List 2 properties of halogens?
- Low melting and boiling points
- Exist as diatomic molecules
What is the trend in reactivity down group 7?
Reactivity decreases because atomic radius and electron shielding increases so the ability to gain an electron decreases.
What is the trend in oxidising ability down the group?
Decreases down the group (Cl strongest and I the weakest), because Cl has the fewest occupied shells it has the greatest attraction between outer electrons and nucleus thus easier to gain electrons
What is the trend in reducing ability down the group?
Decreases down the group (Cl weakest I strongest) because outer electrons are furthest from the nucleus, weaker force of attraction thus easiest to be oxidised
When a more reactive halogen displaces a less reactive halide, what is this reaction called?
Displacement reaction
What is the colour of chlorine in water?
Pale green
What is the colour of bromine in water?
Orange
What is the colour of iodine?
Brown
What is the colour of chlorine in cylohexane?
Pale green
What is the colour of bromine in cylohexane?
Orange
What is the colour of bromine in cylohexane?
Orange
What is the colour of iodine in cylohexane?
Violet
Out of the 3 halide ions which one can be oxidised by chlorine?
Br- and I- ions
Write the equation for chlorine displacing bromide ions?
Cl2 + 2Br -> 2Cl- + Br2
Write the equation for Cl2 oxidising 2I-.
Cl2 + 2I- -> 2Cl- + I2
Out of the 3 halides which one can be oxidised by bromine?
I- ions
Write the equation for bromine displacing iodide ions.
Br2 + 2I- -> 2Br- + I2
Define disproportionation
The oxidation and reduction of the same element in a redox reaction
What is the equation for the reaction of Cl2 with water?
Cl2 + H2O -> HClO + HCL
What type of reaction is the reaction of chlorine with water?
Disproportionation, chlorine is both oxidised and reduced
What acts as a weak bleach in this reaction?
HClO (chloric acid)
What kills the bacteria in this reaction?
ClO- (chlorate ions) and chloric acid
Is chlorine soluble in water?
Insoluble in water but can dissolve in sodium hydroxide
How do you test for carbonates?
- Add dilute acid to a solution containing carbonate ions
- Will cause fizzing/effervescence due to the production of CO2 (limewater confirms the production of CO2)
How do you test for sulphates?
- Firstly add dilute HCl to remove any impurities (carbonates)
- Add barium chloride which contains barium ions and a white precipitate should form
How do you test for halides?
- Firstly add dilute nitric acid to get rid of any impurities (carbonates or sulfite)
- Add silver nitrate to form a precipitate
What colour are the precipitates for each halide ion?
Cl- is a white precipitate
Br- is a cream precipitate
I- is a yellow precipitate
Why is it important to carry out the carbonate test before the sulfate test?
If you carry out a sulfate test on a carbonate you will get a white precipitate too, only proceed to the sulfate test once you know there is no carbonate present
What are the products formed when chlorine reacts with sodium hydroxide?
NaClO, NaCl and H2O
How do you test for ammonium compounds?
- Add sodium hydroxide
- Gently heat and gas will be produced
- Use damp red litmus paper should turn blue
What is the equation for another disproportionate reaction that is found in household bleach?
Cl2 + NaOH -> NaClO + NaCl + H2O
Explain why, if you are testing a mixture, it is important to use dilute nitric acid instead of sulfuric and hydrochloric acid, for the carbonate test?
If sulfuric acid is used, sulfate ions will show up in the sulfate test with Ba2+ and if HCl is used chloride ions will show up in the halide test with Ag+
Explain why group 7 has an increase in boiling point down the group
- Has van der Waals’ forces
- As you go down the group the number of electrons increase so the energy needed to break these forces increases
At stage 1 the student bubbled some chlorine through an aqueous solution of potassium iodide. What would the student see at stage 1?
Goes brown
Halogens have van der Waals’ forces between their molecules.
(i) Describe how van der Waals’ forces arise.
- Uneven distribution of electrons
- Creates an instantaneous dipole
- Causes an induced dipole in neighbouring molecules
