TOPIC 4 - INORGANIC CHEM AND PERIODIC TABLE

Question 1

Why does ionisation energy decrease down Group 2?

Answer 1

The extra inner shells shield electrons
Nucleus is further away from outer electrons due to more shells. Despite the increase in proton number the shielding effect overrides it so it’s easier to remove an electron.

Therefore, reactivity inreases down the gp as IE lowers down gp.

Question 2

group 2 elements produce when they react with water?

Answer 2

Hydroxides (bases/alkaline) and hydrogen.

EXCEPT Be does not react with H20.
Mg reacts very slowly with COLD H2O but vigorously with STEAM produces MgO.

Increasing effervescence, down gp. And Ca produces SOLID hydroxide.

Question 3

group 2 elements produce when they react with oxygen?

Answer 3

Form bases - white powdered metal oxides.
A slow reaction occurs, in which a surface coating of oxygen forms around the element, helping prevent further reaction.
Often stored under oil to keep it reacting with oxygen and water vapour in the air.

Question 4

group 1 & 2 elements produce when they react with chlorine?

Answer 4

• chlorides MCl2

- REDOX

Question 5

group 2 oxides reacting with water?

Answer 5

They form a strongly alkaline solution due to OH- = M(OH)2.

• BeO DOES NOT REACT AT ALL. - INSOLUBLE
• MgO reacts slowly

Question 6

trend in solubility down group 2.

Answer 6

• ANIONS WITH SMALLER CHARGE -1 ARE MORE SOLUBLE DOWN GROUP. BIGGER CHARGE -2 LESS SOLUBLE DOWN GROUP.
• Gp 2 SULPHATES = less soluble down gp. BaSO4 is insoluble.
• Gp 2 hydroxides = more soluble down the gp as they DISSOCIATE MORE - pH INCREASES as OH- RELEASED.
• All group 2 nitrates and chlorides are soluble

Question 7

What is thermal stability?

Answer 7

The measure of how much a compound resists decomposes when heated.

-Group 1 compounds are more thermally stable ( do not decompose) than group 2 compounds

• M carbonates = MO (white solid) + CO2 Only Gp 1 Li carbonate decomposes.
• M nitrate = MO (white solid) + NO2 + O2 -> Gp 2 and LiNO3 produces this as it is the smallest cation.
  OTHER GP 1 NITRATES = KNO2 + O2
• SMALLER AND HIGHER THE CHARGED CATION THE MORE POLARISING THE CATION IS AND LESS THERMAL STABLE THE METAL CARBONATE IS.
  MORE POLARISING = MORE DISTORTION OF e- cloud and weaker the bond btw anion.

Question 8

TESTING THERMAL STABILITY :

NO3-

(CO3)2-

Answer 8

1. • measure how long O2 produced for using gas syringe and relight glowing splint.
     - NO2 produces a brown toxic gas in fume cupboard as safety. NO BROWN FUMES = GP 1 NITRATE AND LESS DECOMPOSITION IF LESS BROWN FUMES.
2. • limewater turns cloudy and more CO2 produced using gas syringe.

Question 9

What causes the colours in flame tests?

Answer 9

• electrons absorb energy and move to a higher energy level
• this electron is now in an excited state.
• the electron immediately drops back to its “ground state”
• this movement releases energy as light
• if the light released is in the visible spectrum we can then perceive it as colour

Question 10

What are the 2 main problems with a flame test?

Answer 10

• Many compounds contain small traces of sodium so the intense colour of Na can mask other colours
• Qualitative test - we all perceive diff colours differently.

Question 11

How do you perform a flame test?

Answer 11

-Safety glasses fume cupboard lab coat
-dip the nichrome wire into the conc HCL then into the
metal compound (powdered)
-hold the end of the wire in the blue flame and observe the colour of the flame

Question 12

FLAME TEST COLOURS:

Answer 12

R, Y/O, L, R/P, B/V, NO, NO, Brick, Cr, Apple Green

Question 13

general trend in melting point down group 7?

Answer 13

• Electronegativity decreases down gp - atomic radius increase, more shielding, lower nuclear attraction harder to gain e-.
• BP INCREASES DOWN Gp as London forces increases gas to solid.

Question 14

DISPLACEMENT REACTIONS

Answer 14

. Add organic solvent (hexane) to see change in colour and halogen (less oxidising) will form a top colour layer I2 = purple.
. More reactive halogen displaces less reactive halide ions as it is easier to gain e-s from a smaller radius.
- REACTIVITY OF GP 7 DECREASES DOWN THE GROUP.
- Cl2 atom does not displace the the same Cl-

Question 15

DISPORPOTIONATION REACTIONS

Answer 15

• halogen and COLD ALKALI (MOH) =
  MX+ MOX + H20
• halogen and HOT ALKALI =
  MXO3 + MX + H2O

Bleach formation :
Cl2 + NaOH ---> NaClO + NaCl +H2O 
. treats water
. cleaning
. bleach paper and fabrics

H2O sterilisation:
H2O + Cl2 reversible reaction = HCl+ HClO
dissociates into H+ & ClO-

Question 16

Halogen and water

Answer 16

= HX e.g. hydroiodic acid - any of them white misty fumes

Question 17

NH3 and Hydrogen halide

Answer 17

= ammonium halide NH4X

Question 18

TEST FOR NH4 COMPOUNDS

Answer 18

• Add NaOH and NH3 ammonia gas produced. This turns damp RED LITMUS TO BLUE.
• NH3 + HCl —> NH4Cl white fumes

Question 19

HALIDE IONS are REDUCING AGENTS

Answer 19

themselves oxidise and cause others to reduce.
- REDUCING AGENTS INCREASE DOWN THE GP and can reduce H2SO4:

NaCl + H2SO4 —> NaHSO4 + HCl
NaBr + H2SO4 —> NaHSO4 + HBr. BUT IT REDUCES FURTHER SO = SO2 (white fumes)+ H20
NaI + H2SO4 —> NaHSO4 + HI but REDUCES FURTHER = SO2 + H20. BUT REDUCES EVEN FURTHER = S + H20 BUT I2 REDUCES SULPHUR MORE ==== H2S (rotten egg smell ) + H20

do this by IONIC EQ made from HALF EQ

Question 20

TEST FOR SULPHATES

Answer 20

• Add HCl to remove carbonates.

. Add BaCl2 and a white precipitate of insoluble BaSO4 forms

Question 21

TEST FOR HYDROXIDES

Answer 21

• RED LITMUS turns BLUE.

Question 22

TEST FOR HALIDE IONS WITH AgNO3

Answer 22

. Add dil HNO3 to remove any carbonate ions
. Then a few drops of AgNO3 sol

AgCl (WHITE PRECIP)
AgBr (cream precip)
AgI ( yellow precip)
AgF is soluble so no precip

hard to differentiate btw colours so additional test 
is adding NH3.
- Cl- dissolves in dil.NH3
- Br - dissolves in concen. NH3
- I -  is insoluble in concen. NH3