CH4: Inorganic Chemistry + Periodic Table

Question 1

Trend of ionisation energy down group 2? How does this explain the reactivity trend down the group?

Answer 1

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

Question 2

Group 2 reactions with water, oxygen ad chlorine ?

Answer 2

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

Question 3

Magnesium’s reactions with water?

Answer 3

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)

Question 4

Why do the oxides form more strongly alkaline solutions down the group ?

Answer 4

Hydroxides get more soluble

Question 5

Group 2 oxides reaction with dilute acid?

Answer 5

MO + 2HCl —> MCl2 + H2O
Reaction with HCl : forms chloride
Reaction with sulphuric acid : forms sulfate

Question 6

Hydroxide reactions with water and dilute acid?

Answer 6

M(OH)2 (s)+ H2O —-> M(OH)2 (aq)

Question 7

Solubility trends of group 2?

Answer 7

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

Question 8

What is thermal decomposition?

Answer 8

the breakdown of a compound into two or more different substances using heat

Question 9

What do group 1/2 carbonates decompose into?

Answer 9

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

Question 10

How do group 1/2 nitrates decompose ?

Answer 10

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

Question 11

Why does the thermal stability of group 1/2 increase down the groups?

Answer 11

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

Question 12

Why are group 2 compounds less thermally stable than group 1 compounds?

Answer 12

Group 2 have 2+ charge

The greater the charge on the cation, greater the distortion, so anions become less stable

Question 13

How to carry out flame tests?

Answer 13

1. Mix compound with HCl
2. Heat piece of platinum/Nichrome wire in hot Bunsen flame
3. Dip wire into compound/acid mixture /hold in flame

Question 14

Flame colours of group1/2 metals?
Li , Na, K, Rb, Cs, Ca, Sr, Ba

Answer 14

Li - red
Na- orange/yellow
K - lilac
Rb - red
Cs - blue
Ca- brick red
Sr- crimson
Ba - green

Question 15

What causes the flame colours ?

Answer 15

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

Question 16

Halogen colours down the group?
F,cl, br,i

Answer 16

F2 - pale yellow gas
Cl2 - green/yellow gas
Br2 - orange /brown liquid
I2 - grey/black solid , purple vapour

Question 17

Why do Mp/Bp increase down group 7?

Answer 17

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)

Question 18

Trend in electronegativity down group 7 ?

Answer 18

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

Question 19

Why does reactivity decrease down group 7?

Answer 19

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

Question 20

How can displacement reactions show the more reactive halogen /best oxidising agent?

Answer 20

Chlorine will displace both bromine/iodine
- so is therefore REDUCED itself (gain electrons) , but acts as an oxidising agent (oxidises bromine/iodine)

Question 21

Observations when chlorine reacts with halides (potassium bromide or potassium iodide)
And what happens when organic solvent is added?

Answer 21

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

Question 22

Halogen reactions with group 1/2 metals ?

Answer 22

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

Question 23

Halogen reactions with Iron ?

Answer 23

Chlorine/bromine can oxidise iron (II) to iron (III)
However, iodine is oxidised from iodide ions when reacted with iron

Question 24

What is a disproportionate reaction?
Example of this in cold alkalis?

Answer 24

Reaction where the same species is both oxidised/reduced
Cold alkalis :
Cl2 + 2NaOH —> NaCl + NaClO + H20
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-

Question 25

Reaction of chlorine with water/ how does it clean water?

Answer 25

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

Question 26

Why does reducing power of halides increase down the group?

Answer 26

Down the group attraction to nucleus is weaker :
Atomic radius increases, more shielding

• can lose electrons easier

Question 27

Reactions of halide ions with sulfuric acid?

Answer 27

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

Question 28

How are halide ions identified in an unknown solution?

Answer 28

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

Question 29

Colour of silver halide solution if it contains : Cl-, Br-, I-

Answer 29

Cl- : white
Br- : cream
I- : pale yellow

Question 30

Reaction of hydrogen with halides?

Answer 30

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