Topic 8A & 8B (Redox reactions & group 1,2)

A
(14, 6, 7)

state the reducing agent in this reaction

Explanation:

D

state the colors produced by the following ions

Li+

Na+

Ba²⁺

K+

Be²⁺

Li+ = red

Na+ = yellow

Ba²⁺ = green

state the colors produced by the following ions

Ca2+

Sr2+

Mg2+

Rb+

Cs+

Ca2+ = (brick) Red

Sr2+ = (crimson) Red

Mg2+ = no color

Rb+ = (reddish) purple

Cs+ = blue /violet

what is the color of:

nitrogen dioxide

K+

Be²⁺

brown

(or reddish-brown)


K+ = purple/ lilac

Be²⁺ = no color

state the result of nitrogen dioxide damp litmus paper test

blue litmus paper turns red

(When NO2 dissolves in water it forms an acid)

What is disproportionation?

One element is both oxidised and reduced.

What happens to ionisation energy down Groups 1/2?

decreases

[down the group the size of the atoms are larger,
so the atomic radius is greater
there is more shielding and less nuclear attraction,
hence electrons can be removed more easily]

Why does ionisation energy decrease down Groups 1/2?

More shells + shielding → weaker nuclear attraction to outer electron.

Why does Group 1/2 reactivity increase down the group?

Outer electrons are lost more easily due to lower ionisation energy.

What type of agents are Group 1/2 metals?

Reducing agents.

Group 1 + water,

what are the products?

Metal hydroxide + hydrogen.

Group 2 + water

what are the products?

Metal hydroxide + hydrogen.

How does Group 2 hydroxide solubility change down the group?

Increases down the group.

How does Group 2 sulfate solubility change down the group?

Decreases down the group.

Why do Group 2 hydroxides become more soluble down the group?

Lattice enthalpy decreases more than hydration enthalpy.

Why do Group 2 sulfates become less soluble down the group?

Hydration enthalpy decreases faster than lattice enthalpy.

What happens to Group 2 carbonate thermal stability down the group?

It increases.

What happens to Group 2 nitrate thermal stability down the group?

It increases.

Why does Group 2 thermal stability increase down the group?

Larger cation → lower charge density → less polarisation → greater stability.

What do Group 2 carbonates form on heating?

Metal oxide + CO₂.

What do Group 2 nitrates form on heating?

Metal oxide + NO₂ + O₂.

Why is Li an exception in Group 1 thermal decomposition?

Li⁺ is small with high charge density and behaves like Group 2.

What is Na's flame colour?

Bright yellow.

What is K's flame colour?

Lilac/pale violet.

What is Ca's flame colour?

Brick red.

What is Ba's flame colour?

Apple green.

What gas turns limewater milky?

CO₂.

What does oxygen do to a glowing splint?

Relights it.

What colour is nitrogen dioxide?

Brown.

How do you test for carbonate ions?

Add dilute acid; CO₂ forms and turns limewater milky.

How do you test for ammonium ions?

Add NaOH and warm; NH₃ turns damp red litmus blue.

How do you test for sulfate ions?

Acidify with dilute HCl, then add BaCl₂ → white precipitate.

Why not use H₂SO₄ to acidify a sulfate test?

It adds sulfate ions and can cause a false positive.

What is concentration in mol dm⁻³?

c = n/V, with V in dm³.

What is the core titration sequence?

Equation → mole ratio → n=cV → unknown moles → unknown concentration.

How do you convert cm³ to dm³?

Divide by 1000.

How can percentage uncertainty be calculated?

(absolute uncertainty ÷ measured value) × 100.

How can percentage uncertainty in a titre be reduced?

Use a larger titre volume.

• more energy needed to break ionic bonds in MgCO3 lattice
  [lattice energy is more exothermic]

• less energy released during hydration of ions

• (down group 2 the solubility of metal hydroxides increases)
  so Ca(OH)₂ is more soluble than Mg(OH)₂
  
  

- so more OH- ions dissolve in solution/ concentration of OH- is greater

What does repeating titrations achieve?

Identifies outliers and improves reliability.