3.1.3 & 3.1.4- The halogens & Qualitative analysis Flashcards
How do the halogens look like and what is their electronic configuration
all have s2 p5
What happens to the boiling point as you go down group 7.
Increase, as the London forces increase due to the size of the atom.
what type of molecules do the halogen exits as ?
Diatomic (br2, cl2 etc)
Explain the term electronegativity and explain what happens to electronegativity as we go down the group.
What do you think will happen between chlorine, bromine and iodine ?
Chlorine displaces them all since its the most reactive.
Bromine displaces only iodine and Iodine displaces none.
- Remember this is because reactivity decreases as we go down group 7.
Fill this table out with the equations and the colours
This is the aq and organic layer
Aq layer - colour of the least reactive solution
Organic layer - colour of the least reactive solution
KCL, KBR and KI in a column(group) and do their waters in a period and fill out the table.
aq is always the colour of the least reactive solution
Why do we use nitric acids and then silver nitrate ?
To remove any interfering ions e.g carbonates which give a white ppt
How do we test for halide ions ?
Add dilute nitric acid (HNO3) and silver nitrate (AgNO3)
Write out the reaction of silver nitrate and the halide ion and their reuslts.
What test do we do after if the colours look to similar ?
The ammonia test.
How do we create bleach ? - what is the equation for this ?
- what type of reaction is this ?
- Uses of one of the products of this reaction
By mixing chlorine and cold sodium hydroxide which forms sodium chlorate(I) + sodium chloride + water
- Used as bleach to disinfect or kill bacteria.
What happens if hot sodium hydroxide is used ?
Sodium chlorate (V) is produced
Uses of chlorine
- Kill bacteria
- Treat drinking water
The reaction of chlorine and water.
- One of its reactants with water.
Rember when you clean the bath and it starts to bur your eye’s its because H3O+ is produced
Risk of using chlorine
- Its toxic
How do we test for CO32- ?
Add a few drops of dilute hydrochloric aciid./HNO3 (nitric acid)
- If carbonate ions are present, the acid will react with them to produce carbon dioxide gas. This reaction will be seen as effervescence (bubbling).
- Then to test for CO2 we do the limewater test.
Or
CO3 2- + 2H+ -> CO2 + H2O (then test for CO2 )
How do we test for Carbon dioxide ?
We do the lime water test.
- We buble gas through lime water.
- Lime water turns milky.
- If carbon dioxide is present, the limewater will turn milky or cloudy as it reacts with the gas to form calcium carbonate (CaCO₃), a white precipitate which makes the limewater milky.
How do we test for sulfate ions ?
Which order are anions tested in and why are they tested in this order.
- To prevent any false positives
- We do carbonate ions first as they produce a white ppt with barium chloride which is obviously the same colour ppt that sulfate ions produce in barium chloride.
- We do sulfate before halides because sliver ions can form a ppt (Ag₂SO₄) with sulfate ions also which gives a false positive.
- By adding barium chloride (BaCl₂) in the presence of dilute nitric acid, you precipitate out barium sulfate (BaSO₄) if sulfate ions are present.
This ensures that sulfate ions are removed before you proceed to the halide test. - And then we do carbonate test before halide test as carbonates form a white ppt with sliver ions (the whole reason why we use nitric acid)
Why do we use dilute nitric acid instead of dilute HCL
HCl introduces chloride ions (Cl⁻) into the solution, which could interfere in the halide test if you’re testing for chlorides (Cl⁻) in the next step.
How do we test for ammonium ions NH4+
Test for ammonium ion NH4+ by the reaction with warm NaOH(aq), forming NH3 gas.
- Red litmus paper turns blue
How do we test for hydroxide ions ?
Hydroxides are alkaline so red litmus paper will turn blue,
Type of forces in halogens
London forces or for ms sake say van der wals forces
