inorganic chemistry and the periodic table Flashcards
why does ionisation energy decrease down group 2?
-electron shells of elements increase by 1 down G2
-extra inner shells shield outer electrons from attraction of positive nucleus
-atomic radius increases=outer electrons further away from nucleus=reduction in electrostatic attraction
-these factors make it easier to remove outer electrons∴ionisation energy decreases
does the increase in positive charge of the nucleus (due to extra protons) affect ionisation energy of group 2 elements?
no, effect is overridden by extra shells
what is the trend in reactivity down group 2?
increases down the group
what is the trend in ionisation energy down group 2?
decreases down the group
why does reactivity increase down group 2?
elements of G2 react by losing outer 2 electrons ∴ higher ionisation energies makes it more difficult to lose the outer 2 electrons ∴ will be less reactive
what happens when a group 2 metal reacts with water?
forms a metal hydroxide and hydrogen
Ca + 2H₂O→Ca(OH)₂ + H₂
How does Be react with water?
doesn’t react
How does Mg react with water?
very slowly
How does Ca react with water?
steadily
How does Sr react with water?
fairly quickly
How does Ba react with water?
rapidly- effervescence
what happens when a group 2 metal burns in oxygen?
solid white oxide formed
2Ca + O₂→2CaO
what happens when a group 2 metal reacts with chlorine?
forms solid white chlorides
Ca + Cl₂ → CaCl₂
what are the oxides and hydroxides of group 2?
bases
what happens when oxides and hydroxides of group 2 react with dilute acids?
they neutralise the dilute acids because they are bases,, also form solutions for corresponding salts
what happens when oxides and hydroxides of group 2 react with water?
form alkaline solutions,, more alkaline as you go down the group
why do oxides form more strongly alkaline solutions as you go down the group?
the hydroxides get more soluble
what is the trend in solubility of group 2 hydroxides (and other singly charged ions) down the group?
increased solubility
what is the trend in solubility of group 2 doubly charged negative ions (e.g. SO₄²⁻ sulfates) down the group?
decrease solubility
is barium sulfate completely insoluble?
yes
what substance helps detect carbonate ions and hydrocarbonate ions?
HCl
what happens when HCl and CO₃²⁻/HCO₃⁻ react?
they fizz and give off CO₂
CO₃²(s) + 2H⁺(aq) → CO₂(g) + H₂O(l)
how can you test for CO₂?
lime water goes cloudy
how do you test for sulfates?
HCl and Barium Chloride
how do you identify a sulfate ion?
-add dilute HCl followed by Barium chloride solution
-if white participate of barium sulfate forms it means the original compound contained a sulfate
why is HCl added in the test for sulfate ions?
to get rid of traces of carbonate ions so they don’t affect results
how to test for ammonium compounds?
-damp red litmus paper
-because ammonia gas (NH₃) is alkaline it will turn the red litmus paper blue
how to test for ammonium ions (NH₄⁺)?
-add sodium hydroxide to unknown substance into a test tube and gently heat the mixture
-if ammonia is given off NH₄⁺ ions are present
-this can be tested using damp litmus paper
why does litmus paper need to be damp when testing for ammonia gas?
so the gas can dissolve and make the colour change
why is beryllium oxide an exception from the oxides of the group 2 metals?
it does not react with water
what happens when oxides of group 2 are with water?
they react readily and form soluble metal hydroxides that are very alkaline due to the OH⁻
why is magnesium oxide an exception from the oxides of the group 2 metals?
reacts slowly and the hydroxide formed is not very soluble
what is thermal decomposition?
when a substance breaks down when heated
the more thermally stable a substance is…..
the more heat it will take to break it down
what colour will the reaction mixture turn if bromine is displaced?
orange
what colour will the reaction mixture turn if iodine is displaced?
brown
how else can you see the results of a halide-halogen redox reaction?
by shaking the mixture with hexane (organic solvent) so halogen will dissolve and settle as a distinct layer above aqueous solution
how is chlorine used in water treatment to kill bacteria?
-mixing chlorine and water is a disproportionation reaction which produces HCl and HClO(hypochlorous acid)
-HClO ionises to make chlorate ions which kill bacteria in water
flame colour Li?
red
flame colour Na?
orange/yellow
flame colour K?
lilac
flame colour Rb?
red
flame colour Cs?
blue
flame colour Ca?
brick-red
flame colour Sr?
crimson
flame colour Ba?
green
why do the flames colour of group 1 and 2 elements vary?
-energy absorbed from flame causes electrons to move to higher energy levels
-colour seen as electron falls back to lower energy level releasing energy in the form of light
-difference in energy between higher and lower levels determines wavelength of light released (determines colour of light)
why does thermal stability of carbonates and nitrates increase down groups 1 and 2?
halogen + group 1/2 metal?
halide salt
how are halide salts formed?
halogen oxidises group 1/2 metals (halogen reduced itself)
why should reactions involving halogens be carried out in a fume cupboard?
halogens are toxic
what happens when a cold alkali reacts with a halogen?
disproportionation reaction (halogen is simultaneously reduced and oxidised)
how is bleach formed?
disproportionation reaction with chlorine gas + cold dilute aqueous 2NaOH
NaCl also formed and water
what is the chemical name for bleach?
sodium chlorate I (NaClO)
what is the trend in reducing power for the halides? (halogen ions)
reducing power decreases down the group because=
-ions get bigger down the group=electrons further away from nucleus=attraction gets weaker=electron is lost easily
-there are extra inner electron shells so shielding effect is greater
what happens in the reaction of KF/KCl with sulfuric acid?
-HF/HCl produced, misty fumes
-Fluoride and chloride ions are not strong enough reducing agents to reduce sulfuric acid so reaction stops
-not a redox reaction
what happens in the reaction of KBr with sulfuric acid?
-HBr formed (first step),, misty fumes
-HBr further reduces sulfuric acid (as it is a stronger oxidizing agent) into Br₂+SO₂+H₂O (second step),, orange fumes of bromine released,,redox reaction
are halide ions reduced or oxidised in their reactions with H₂SO₄?
oxidised, they lose electrons and become positive
what happens in the reaction of KI with sulfuric acid?
-HI formed (first step)
-HI reduces H₂SO₄ into I₂+SO₂+H₂O
-iodine ions are strong reducing agents so further reduce SO₂ to H₂S which smells of rotten egg
why are iodine ions the strongest reducing agents?
because iodine ions reduces sulfur in H₂SO₄
from +6 to 0,,,, Br goes from +6 to +4
what happens what hydrogen halides gases dissolve in water?
they become acids as hydrogen halides are acidic gases e.g. hydrogen chloride to hydrochloric acid
what happens when a hydrogen halide reacts with ammonia gas?
white fumes produced forming NH₄Cl
What to halide ions react with to form precipitate which is a test for halides?
silver nitrate solution AgNO₃
what is the hazard of silver nitrate?
corrosive
what precipitate is formed in the silver nitrate test for fluoride?
there is no precipitate as AgF is soluble
what precipitate is formed in the silver nitrate test for chloride?
white (milk)
what precipitate is formed in the silver nitrate test for bromide?
cream (cream)
what precipitate is formed in the silver nitrate test for iodide?
yellow (butter)
How can you further tell what halide has been identified from silver nitrate test if precipitates look similar?
add ammonia solution
Silver chloride (AgCl) dissolves in dilute ammonia.
Silver bromide (AgBr) dissolves in concentrated ammonia but not in dilute.
Silver iodide (AgI) is insoluble in ammonia.
what happens when ammonia solution is added to AgCl precipitate?
precipitate dissolves in dilute ammonia solution to make colourless liquid
what happens when ammonia solution is added to AgBr precipitate?
only dissolves in concentrated ammonia solution to give colourless solution (would not happen in dilute)
what happens when ammonia solution is added to AgI precipitate?
doesn’t dissolve at all regardless of concentration
