CH4: Inorganic Chemistry + Periodic Table Flashcards
Trend of ionisation energy down group 2? How does this explain the reactivity trend down the group?
DECREASES:
Extra inner shells shield outer electrons from attraction to nucleus
- also larger atomic radius down the group —> less electrostatic attraction to nucleus
The higher the first/second ionisation energies - need more energy to lose an electron - so *less likely to lose electron —> less reactive
Ionisation energy decreases, reactivity increases
Group 2 reactions with water, oxygen ad chlorine ?
WATER : M + 2H20 —> M(OH)2 + H2
Metal hydroxide and hydrogen (beryllium oxide doesn’t react with water)
OXYGEN : 2M +O2 —> 2MO
Form oxides
CHLORINE : M + Cl2 —> MCl2
Form chlorides
Magnesium’s reactions with water?
Mg (s) + 2H2O (l) → Mg(OH)2 (aq) + H2 (g)
- reacts extremely slowly in cold water (mg hydroxide and hydrogen)
- Solution formed is weakly alkaline (pH 9-10) as magnesium hydroxide is only slightly soluble
- magnesium is heated in steam, forms magnesium oxide and hydrogen gas:
Mg (s) + H2O (g) → MgO (s) + H2 (g)
Why do the oxides form more strongly alkaline solutions down the group ?
Hydroxides get more soluble
Group 2 oxides reaction with dilute acid?
MO + 2HCl —> MCl2 + H2O
Reaction with HCl : forms chloride + water
Reaction with sulphuric acid : forms sulfate + water
Hydroxide reactions with water and dilute acid?
M(OH)2 (s)+ H2O —-> M(OH)2 (aq)
Solubility trends of group 2?
Compounds of group 2 elements that contain single charged negative ions (OH-) INCREASE in solubility down the group - ALSO INCREASES ALKALINITY
Compounds with double charged negative ions (SO4 2-) decrease in solubility down the group
What is thermal decomposition?
the breakdown of a compound into two or more different substances using heat
What do group 1/2 carbonates decompose into?
GROUP 1 : thermally stable , so Bunsen can’t make them decompose (EXCEPT LITHIUM CARBONATE —> forms lithium oxide/co2 )
GROUP 2 : Metal oxide and carbon dioxide gas
How do group 1/2 nitrates decompose ?
GROUP 1 : Decompose to form metal NITRITE (NO2 -) /oxygen
Except lithium nitrate : forms nitrogen dioxide , lithium oxide and oxygen
GROUP 2: forms oxide, nitrogen dioxide (toxic), and oxygen
Why does the thermal stability of group 1/2 increase down the groups?
Cation ( + ions) POLARISE the anions (- ions - nitrate /carbonate ions) , distorting it
The greater the distortion , the less stable it is
LARGER CATIONS CAUSE LESS DISTORTION THAN SMALLER CATIONS, bc they have lower charge density
- down the group, cations are larger, so less charge density and less distortion caused —> MORE STABLE
Why are group 2 compounds less thermally stable than group 1 compounds?
Group 2 have 2+ charge
The greater the charge on the cation, Polarises anion more, greater the distortion —> C-O or N-O bond weakened more - anions become less stable
How to carry out flame tests?
- Mix compound with HCl
- Heat piece of platinum/Nichrome wire in hot Bunsen flame
- Dip wire into compound/acid mixture /hold in flame
Flame colours of group1/2 metals?
Li , Na, K, Rb, Cs, Ca, Sr, Ba
Li - red
Na- orange/yellow
K - lilac
Rb - red
Cs - blue
Ca- brick red
Sr- crimson
Ba - green
What causes the flame colours ?
Electrons get excited and move to higher energy kevel
As electron falls back down to lower energy levels, they release energy in form of light
- the difference in energy between the higher/lower levels determines the wavelength of light released
Halogen colours down the group?
F,cl, br,i
F2 - pale yellow gas
Cl2 - green/yellow gas
Br2 - orange /brown liquid
I2 - grey/black solid , purple vapour
Why do Mp/Bp increase down group 7?
Increase in electron shells down the group, STRONGER LONDON FORCES
- harder to overcome, so higher MP/BP
As MP/BP increase down the group, the volatility decreases
- it iS more volatile if its easier to evaporate (lower BP)
Trend in electronegativity down group 7 ?
How strongly atoms attracts electrons to itself in a covalent bond
ELECTRONEGATIVITY DECREASES down the group as:
- atomic radii increase down group (outer shells further for nucleus ) —> less attraction to nucleus
- more shielding down the group
Harder to attract electron (oxidising power) decreased
Why does reactivity decrease down group 7?
Halogens reacts by GAINING AN ELECTRON (-1 IONS)
- so has been reduced/acts an oxidising agent
As you go down group :
Atomic radii increases/shielding increases, so less attraction to nucleus —> harder to attract electrons
How can displacement reactions show the more reactive halogen /best oxidising agent?
Chlorine will displace both bromine/iodine
- so is therefore REDUCED itself (gain electrons) , but acts as an oxidising agent (oxidises bromine/iodine)
Observations when chlorine reacts with halides (potassium bromide or potassium iodide)
And what happens when organic solvent is added?
Chlorine + Potassium Bromide :
Solution become YELLOW - ORANGE (bromine formed)
Cl2 + 2Br - —> 2Cl- + Br2 ( Chlorine is reduced , gains electrons as it displace bromine)
IF ORGANIC SOLVENT ADDED : layer will be yellow orange
Chlorine + Potassium Iodide:
Solution becomes brown (iodine formed)
Cl2 + 2I - —> 2Cl- + I2
IF ORGANIC SOLVENT ADDED : layer will be PURPLE
Halogen reactions with group 1/2 metals ?
Form ionic compounds which are halide salts
2Na + Cl2 —> 2NaCl
Na is oxidised , bc oxidation no goes from 0 to +1
SO HALOGENS ACT AS OXIDISING AGENTS
Halogen reactions with Iron ?
Chlorine/bromine can oxidise iron (II) to iron (III)
However, iodine is oxidised from iodide ions when reacted with iron
What is a disproportionate reaction?
Example of this in cold DILUTE alkalis?
Reaction where the same species is both oxidised/reduced
Cold alkalis :
Cl2 + 2NaOH —> NaCl + NaClO + H20
Forms sodium chlorate(I) - used for bleach
Ionic equn: Cl2+ 2OH- —> Cl- + ClO-+ H20
Chlorine is oxidised(OX number goes from 0 TO +1 ) for Cl2 to ClO-
Chlorine is reduced (OX number goes from 0 to -1) for Cl2 to Cl-
Reaction of chlorine with water/ how does it clean water?
CL2 + H20 —> HCl + HClO
OX NUMBERS: 0 -1
0 +1
- DISPROPORTIONATE REACTION
Chloric acid sterilises water by killing bacteria
Chloric acid can further dissociate in water to from ClO-
HClO —> H+ + ClO-
ClO- can be used as a sterilising agent
Why does reducing power of halides increase down the group?
Down the group attraction to nucleus is weaker :
Atomic radius increases, more shielding
- can lose electrons easier
Reactions of halide ions with sulfuric acid?
Chloride ions:
H2SO4 (l) + NaCl (s) → HCl (g) + NaHSO4 (s)
- white fumes seen bc of HCl gas
Bromide ions:
H2SO4 (l) + NaBr (s) → HBr (g) + NaHSO4 (s)
- misty fumes from HBr gas
2HBr (g) + H2SO4 (l) → Br2 (g) + SO2 (g) + 2H2O (l)
Sulfuric acid oxides HBr TO FORM BROMINE /acid is reduced into SO2
- bromine is reddish-brown gas
Iodine ions :
H2SO4 (l) + NaI (s) → HI (g) + NaHSO4 (s)
2HI (g) + H2SO4 (l) → I2 (g) + SO2 (g) + 2H2O (l)
- sulfuric acid oxidises HI /itself is reduced to SO2
Iodine is seen as purple vapour
6HI (g) + H2SO4 (l) → 3I2 (g) + S (s) + 4H2O (l)
Sulfuric acid oxides HI again/itself is reduced to SULFUR - YELLOW SOLID
8HI (g) + H2SO4 (l) → 4I2 (g) + H2S (s) + 4H2O (l)
Sulfuric acid oxidises HI again/ itself reduced to hydrogen sulfide (H2S) - BAD EGG SMELL
How are halide ions identified in an unknown solution?
Dissolving solution in NITRIC ACID + silver nitrate + ammonia
Nitric acid remove ions that interfere with reaction
React with silver nitrate like this:
Ag+ (aq) + Cl- (aq) → AgCl(s)
If halide ion present , precipitate of silver halide formed (AgX)
Reacting silver halide solution with ammonia :
If precipitate dissolves in diluteammonia —> CHLORIDE
If precipitate doesn’t dissolve in dilute ammonia, but in concentrated—> BROMIDE
If precipitate doesn’t dissolve in either —> IODIDE
Colour of silver halide solution if it contains : Cl-, Br-, I-
Cl- : white
Br- : cream
I- : pale yellow
Reaction of hydrogen with halides?
Forms hydrogen halide (e.g hydrogen chloride)
1) Hydrogen halides react with ammonia gas to from AMMONIUM HALIDES
2) Hydrogen halides react with water :
Hydrogen chloride + water —> Hydrochloric acid
Test for sulfate ions?
Add dilute HCl and barium chloride solution
- white precipitate forms if sulfate present
HCl added to remove any carbonate/sulfate ions
Test for ammonium compounds?
If ammonia is present , turns red litmus paper, blue
Devise a procedure to identify the nitrates if lithium,rubidium and strontium using heat /any precipitation reactions of the compounds? (6)
- no brown gas on heating RbNO3 (group 1 so doesn’t produce nitrogen dioxide)
-
brown gas on heating LiNO3 and Sr(NO3)2
Dissolveall - add H2SO4
- white precipitate for Sr(NO3)2 - solubility of group 2 sulfate decrease down the group so sulfate ions stay as precipitate
- no precipitate for LiNO3 or RbNO3 - group 1 compounds soluble in water
Group 1 hydroxides are __________
MORE SOLUBLE than group 2 hydroxides
( all group 1 compounds are soluble in water so don’t form precipitates when testing for cations , therefore use flame test!!!)
Describe apparatus used to compare decomposition of metal carbonates and how rate of decomposition can be compared? (2)
Use delivery tube to bubble gas into limewater
Compare time taken for limewater to go cloudy
Hydrogen halide reaction with water?
HX(g) + H2O(l) ➔ H3O+(aq) + X-(aq)
Form acidic solutions
Produce strong acids as hydrogen halides FULLY DISSOCIATE in water —> turn blue litmus paper, RED (as its acidic)
When exposed to moist air/vapour, hydrogen halides form MISTY FUMES due to formation of droplets of aqueous acid solution
Reaction of hydrogen halides with ammonia?
HX(g) + NH3(g) ➔ NH4X(s)
Acid-base reaction producing WHITE FUMES (due to NH4X (s))
Chlorine reacting with HOT concentrated alkali - NaOH ?
3Cl2(g) + 6NaOH(aq) ➔ NaClO3(aq) + 5NaCl(aq) + 3H2O(l)
Produces sodium CHLORATE (V)
Ox number of chlorine : from 0 to +5 (NaClO3)
From 0 to -1 (in NaCl)
ClO3- are powerful oxidising agents used for bleaching paper/textiles
Test for carbonate ions/hydrogen-carbonate ions?
Add dilute nitric acid
Effervescence due to CO2
Confirm presence of CO2 by passing bubbles of gas through limewater in a connecting test tube
- limewater goes cloudy if CO2 present (due to calcium carbonate precipitate)
CO2(g)+ Ca(OH)2 (aq)—> CaCO3(s) + H2O (l)
Test for AMMONIUM IONS?
Add NaOH drop wise to sample + warm gently
Hydroxide ions react with NH4+ ions :
OH-(aq) + NH4+(aq) ➔ NH3(g) + H2O(l)
Moisten piece of red litmus and hold over test tube = paper will go blue if ammonia gas is present confirming ammonium ions were originally present in sample
