Chapter 8 - Reactivity Trends Flashcards
Group 2, The halogens and Quantitative analysis.
What is a reducing agent?
A species that donates it’s electrons to another species, thereby reducing that species.
Which group are reducing agents commonly found?
Group 2
What is the trend in reactivity down group 2?
Reactivity increases.
Explain the trend of reactivity down group 2
Increased atomic radius and shielding effect so ionisation energies decrease. Therefore it’s easier to lose electrons.
What are the products of a group 2 element reacting with water?
Metal hydroxide and hydrogen
What is the product of a group 2 element reacting with oxygen?
Metal oxide
What is the trend of solubility down group 2?
Increases
Explain the trend of solubility down group 2
Down the group, the solution has a greater concentration of OH-.
Given that group 2 oxides, hydroxides and carbonates neutralise acids, what can they be referred to as?
Bases
Given that most group 2 oxides, hydroxides and carbonates are soluble in water, what are they also besides bases?
Alkalis
What is the use of calcium hydroxide in agriculture?
Increases the pH of acidic soils.
Ca(OH)(2) + 2H+ -> Ca2+ + 2H(2)O
How are group 2 compounds used in medicine?
Used in indigestion tablets as antacids, often a suspension of a metal hydroxide in water.
What is another name for group 2?
Alkaline Earth Metals
What is another name for group 7?
Halogens
What is the trend in boiling point down group 7?
Increases
Explain the trend in boiling point down group 7
More electrons,
Stronger London forces,
More energy to break intermolecular forces,
Boiling point increases.
What is the trend in reactivity down group 7?
Reactivity decreases
Explain the trend in reactivity down group 7
Atomic radius increases, More inner shells, Shielding increases, Nuclear attraction decreases, Reactivity increases
What do more reactive halogens do to less reactive halide ions?
Displace them
What can displacement reactions be used to identify?
Which halide is present in solution.
Which compound is used to test for halides?
Silver nitrate solution
How can the results for a halide test be further tested?
Solubility in ammonia solution
What is disproportionation?
A redox reaction in which the same element is both oxidised and reduced.
Describe the test for carbonates
Carbonates react with acids to form carbon dioxide gas.
Add dilute nitric acid to testing solution. If bubbles observed could be a carbonate. To prove its CO(2), bubble gas through lime water, a white precipitate will form.
Describe the test for sulphates
Aqueous barium ions are added to the solution. If a white precipitate forms, there is a sulphate.
In the halide tests, what happens to chloride with silver nitrate and then ammonia
Silver nitrate - white precipitate
Ammonia - soluble in dilute ammonia
In the halide tests, what happens to bromide with silver nitrate and then ammonia
Silver nitrate - cream precipitate
Ammonia - soluble in concentrated ammonia
In the halide tests, what happens to iodide with silver nitrate and then ammonia
Silver nitrate - yellow precipitate
Ammonia - insoluble in concentrated ammonia
What is the correct order for these anion tests?
Carbonate test, sulphate test, halide test
Why is this the correct order for anion tests carbonate, sulphate, halide?
Carbonates also form a white
precipitate in the sulphate test such as barium carbonate but not vice versa. So first must rule out there isn’t any carbonates present
Carbonates and sulphates form precipitates with silver nitrate. Such as Ag2CO3 and Ag2SO4.
Describe the test for ammonium ions
Add aqueous NaOH to the solution,
Ammonia gas is produced,
Can be detected with moist indicator paper as it will turn blue.
If I want to work out which halide is present in a solution what can I do
Run a displacement reaction
A Cl2 is added to a Br- ion. What observation will you see with and without the polar solvent cyclohexane present
Orange colour will form as the chlorine would have displaced the bromide ion
With cyclohexane - you will see a orange colour
A Cl2 is added to a I- ion. What observation will you see
Brown colour change as the chlorine would have displaced the Iodine ion
In cyclohexane - it is violet colour
A Br2 is added to a I- ion. What observation will you see
Brown colour change as the halogen would have displaced the Iodine ion
In cyclohexane- it would be a violet colour change
What colour is Cl2 in water
Pale green
What colour is fluorine
Pale yellow
Describe the astatine
Rare, radioactive and decays rapidly
Least reactive halogen
What groups are the best oxidising event and describe the oxidising trend as you go down the group
Halogens
As you go down the group the halogens become weaker oxidising agents
What compound neutralises stomach acid
Magnesium hydroxide
Calcium carbonate
At RTP describe chlorine, bromine and iodine
Chlorine is a pale green gas
Bromine liquid is extremely toxic, and vaporises readily arises RTP.
Iodine is a solid with grey-black crystals
Show the reaction of chlorine with water and what kind of reaction is this
Cl2(aq) + H20(l)»_space;> HCLO(aq) + HCL(aq)
Disproportionation reaction
Show the reaction of chlorine with cold, dilute aqueous sodium hydroxide and what kind of reaction is this
Cl2(aq) + 2NaOH(aq)»_space;> NaCLO(aq) + NaCl(aq) + H20(l)
What do household bleach contain
Sodium chlorate (I), NaCLO made by reacting chlorine with sodium hydroxide
Benefits and risk of chlorine use
Disinfectant for water
Ensure no disease breakout
Respiratory irritant
Cause cancer b/ of the formation of chlorinated hydrocarbons
Explain the test that would be carried out on a mixture of ions
Carbonate test:
If you see bubbles, continue adding dilute nitric acid until the effervescence stops
All carbonate ion will then have been removed and there will be none left to react in the next tests. We don’t use sulfuric acid or hydrochloric acid because it contains sulfate and chloride ions , which will show
Up in the sulfate and halide test
Sulfate test:
Add an excess of Ba(NO3)2
Any sulfate ion present will precipitate out as barium sulfate
Filter the solution to remove the barium sulfate
Halide test:
Any carbonate or sulfate ion present have already been removed. Therefore any PPT must involve halide ions.
Add NH3 to confirm which halide you have
