C8- Reactivity trends Flashcards
(42 cards)
Why can group 2 alkaline metals be called reducing agents
The group 2 agent reduces another species
Another species will gain the two electrons and be reduced
Group 2 agent itself is reduced
Reaction of group 2 with oxygen
Always forms metal oxides
e.g. MgO, CaO
Reaction of group 2 with water
Forms an alkaline hydroxide and hydrogen gas
Forms OH- ions in solution
Reactivity down group 2
Increases down the group
Increased shielding
Increased atomic radius
Decreased nuclear attraction
Less energy need to remove outer e-
First ionisation energy down group 2
Decreases down the group
Reduced nuclear attraction as a result of increased shielding and decreased atomic radius
Group 2 oxides in water
Release OH- ions into solution
–> forming an alkaline solution of metal hydroxide
If oversaturated further metal or OH- ions will be precipitated into solution
Solubility of group 2 hydroxides in water
trend + effect
increases down the group
resulting solutions are more alkaline
Thus alkalinity increases down the group
2 uses of group 2 compounds as bases
Agriculture- CaOH2 increases the pH of acidic soil, neutralising it and producing neutral water
Medicine- Antacids or indigestion, as it neutralises the HCl form the stomach
Physical properties of halogens
Don’t occur in elemental form in nature
E.g. salt or dissolved in oceans
Boiling point of halogens
trend + explanation
Increases down the group
More electrons
stronger London forces
More energy needed to break intermolecular forces
Bp increases
Why can halogens be called oxidising agents
Another species looses electrons to the halogens, oxidising it
Halogen oxidises another species
is itself reduced
Fluorine is the strongest oxidising agent
halogens in cyclohexane
Dissolve more readily in cyclohexane than in water
Disproportionation reaction
Redox reaction were the same element is bot oxidised and reduced
Chlorine in water
reaction + bacteria
Disproportionation reaction that produces HCl and HClO
Its the acids not chlorine tat kills bacteria in the water
Reduces incidence of water borne diseases
Chlorine and cold aqueous sodium hydroxide
Chlorine has a low solubility in water
When the water contains dissolves NaOH, much more CL2 then dissolves
Another disproportionation reaction takes place
Benefits and risk of chlorine usage
Cl2 is a toxic gas
a respiratory irritant
in large concentrations lethal
Cl2 can react with hydrocarbons, producing carcinogenic chlorinated hydrocarbons.
the overall risk of not using Cl2 is far greater than using it
Carbonate test
add acid
positive- forms carbon dioxide gas (bubbles)
typically use nitric acid
CO2 test
Bubble gas through limewater
–> calcium hydroxide
turns cloudy as calcium carbonate is formed
Sulfate test
add aqueous barium nitrate or barium chloride
white precipitate forms
–> barium sulfate
halide test
add aqueous silver nitrate
silver halide precipitate forms
add ammonia to test solubility of precipitate- iodine insoluble but cl and br are soluble
Halide test colours
Chlorine- white
Bromine- cream
Iodine- yellow
correct sequence for anion tests
carbonate
sulfate
halide
Why must carbonate test be done first
reduces chances of incorrect conclusion
only one test produces bubbles
carbonate will also form a white precipitate within the sulfate test
Mixture of ions
qualitative tests
do carbonate test until no more bubbles- all carbonate ion shave reacted- must use nitric acid not sulfuric acid as about to do sulfate test
use same mixture
filter out barium sulfate- don’t use barium chloride if doing halide test use barium nitrate
