Inorganic chemistry and the Periodic Table

Question 1

What is the trend in ionisation energy for group 2?

Answer 1

Decreasing

As you descend Group 2, there are more shells of electrons, so the outer shell electron being removed is further from the nucleus + more shielded (this outweighs the increase in nuclear charge). Therefore attraction to the nucleus decreases

Question 1

What is the trend in atomic radius in group 2 (and 1)?

Answer 1

Increasing

More shells of electrons + more shielding so electron are further away from nucleus + less tightly held therefore atom gets bigger

Question 2

What is the trend in reactivity in group 2 (and group1)?

Answer 2

Reactivity increases/gets more vigorous
As you go down the group, the number of shells of electrons increases

• So the outer electron being lost is further from the nucleus and more shielded (this outweighs the increased nuclear charge)
• Therefore, the electron is more easily lost and the element is more reactive

Question 3

What are the trends in solubility of hydroxides and sulphates for group 2?

Answer 3

Hydroxides - more soluble down the group
Sulfates - less soluble down the group

Question 4

What is the trend in thermal stability of nitrates and carbonates?

Answer 4

As you go down group 2, the thermal stability increase
- The size of the cation increases
- So polarises the anion less

Question 5

What is the trend in group 1 for nitrates and carbonates?

Answer 5

All group 1 nitrates decompose when strongly heated

Question 6

What does lithium nitrate decompose to form? Why?

Answer 6

4LiNO3 → 2Li2O + 4NO2 + O2
Lithium is so strongly polarising that it causes the nitrate ion to break down

Question 7

Why do the other group 1 nitrates melt rather than fully decompose?

Answer 7

2NaNO3 → 2NaNO2 + O2
This is because the other group 1 cations have a lower charge density so are not as strongly polarising

Question 8

Why does only lithium carbonate decompose?

Answer 8

Li2CO3 → Li2O + CO2
Lithium is so strongly polarising that it causes the carbonate ion to break down. However other Group 1 carbonates will not decompose when heated, as the cations are not strongly polarising enough

Question 9

What is the reaction of Group 2 metals with chlorine:

Answer 9

Metal + chlorine → metal chloride (salt)

Question 10

What is the reaction of Group 2 metals with water:

Answer 10

Metal + water → metal hydroxide + hydrogen

Question 11

What is the reaction of Group 2 metal oxides with water:

Answer 11

Metal oxide + water → metal hydroxide

Question 12

What is the reaction of Group 2 metal oxides with acids:

Answer 12

Metal oxide + acid → metal salt + water

Question 13

What is the reaction of Group 2 hydroxides with acids:

Answer 13

Metal hydroxide + acid → metal salt + water

Question 14

Describe the method for a flame test:

Answer 14

1. Clean a platinum or nichrome wire by heating it in a non-luminous Bunsen burner flame, dipping it into a little concentrated hydrochloric acid on a watch glass and heating it again. Continue this until the wire produces little or no colour in the flame
2. Dip the clean wire into the acid and then into a small portion of powdered compound on a watch glass.
3. Hold the wire so that the powdered solid is in the edge of the flame and note any colour change
4. Observe the flame through a diffraction grating or direct vision spectroscope

Question 15

What are the different colour of flames:

Answer 15

Calcium - Orange
Magnesium - no colour
Lithium - Crimson Red
Barium - apple green
Sodium - Yellow
Potassium - lilac

Question 16

What are the origins of colour in the flame test?

Answer 16

• Energy provided by the flame allows an electron to be ‘excited’
• This configuration is unstable, so the electron will return to its original energy level (relaxation)
• Extra energy will then be emitted in the form of light
• The difference in energy between the different electron shells determines the wavelength and therefore colour of the light emitted

Question 17

Why do some elements not have colour?

Answer 17

• The energy provided is not sufficient to excite an outer shell electron between energy levels
• The light emitted might have a wavelength which is not in the visible range of light

Question 18

Why do some elements not have colour?

Answer 18

• The energy provided is not sufficient to excite an outer shell electron between energy levels
• The light emitted might have a wavelength which is not in the visible range of light

Question 19

What are the appearances for the different halogens:

Answer 19

Chlorine - pale yellow gas
Bromine - reddish brown liquid
Iodine - grey solid/purple vapour

Question 20

What is the trend for the boiling points?

Answer 20

Down the group - boiling point increases

The London forces between the molecules of the halogen get stronger as there are more electrons/a bigger Mr. So it takes more energy to overcome them

Question 21

Explain the trend for reactivity of halogens:

Answer 21

Reactivity decreases
- Down the group, more shells of electrons therefore shielding + distance from the nucleus increase
- This outweighs the increases nuclear charge
- Therefore there is a weaker attraction of outer electron to the nucleus - so harder to gain an electron

Question 22

What is the trend for electronegativity of halogens?

Answer 22

Down the group, electronegativity decreases (harder to attract an electron)
- Distance from nucleus increases (more shells of electrons)
- Shielding increases
- These 2 factors outweigh the increased nuclear charge
- So the attraction to the nucleus is weaker

Question 23

Why is iodine a better reducing agent than bromine?

Answer 23

Iodine reduces the sulphur the furthest, so it is the best reducing agent/has the most reducing power

Question 24

What is the test for sulphate ions:

Answer 24

Add acidified barium chloride
Result = white ppt forms
(HCl added first will remove any OH- or CO32- ions that would also give a white ppt)

Question 25

What is the test for halide ions:

Answer 25

Add acidified silver nitrate
Result = Cl- = white ppt, Br- = cream ppt, I- = yellow ppt
The precipitates form because silver halides are insoluble

Question 26

Test for carbonate ions:

Answer 26

Result = effervescence (of CO2), limewater turns cloudy

Question 27

What happens when chlorine reacts with water:

Answer 27

Cl2 + H2O -> HCl + HOCl
Disproportionation

Question 28

What happens when chlorine react with cold dilute sodium hydroxide?

Answer 28

Cl2 + 2NaOH -> NaCl + NaOCl + H2O
Disproportionation

Question 29

What happens when chlorine react with hot concentrated alkali?

Answer 29

3Cl2 + 6NaOH -> NaClO3 + 5NaCl + 3H2O
Disproportionation

Question 30

What happens when hydrogen halides react with ammonia?

Answer 30

HCl + NH3 -> NH4Cl

Question 31

What happens when hydrogen halides react with water?

Answer 31

HBr + H2O -> H3O+ + Br-

Question 32

What happens when solid KCl react with concentrated sulphuric acid?

Answer 32

KCl + H2SO4 -> HCl + KHSO4
No further reaction occurs

Question 33

What happens when solid KBr halide react with concentrated sulphuric acid?

Answer 33

KBr + H2SO4 -> HBr + KHSO4
2HBr + H2SO4 -> Br2 + SO2 + 2H2O