Unit 5 chem expermient content

Group 2 reactivity with water

Increases down group

• Mg very slow - react with steam

• Ca - fizzing cloudy solution

• Ba - Very vigorous

Explain reactivity trend in group 2

Increase down group

• Bigger atoms

• More shielding

• Easier to lose electrons

Group 2 OH^- CO₃^2- SO₄^2- PPT

Mg

• OH → white ppt

• CO₃^2- → White ppt

• SO₄^2- → Soluble

Ca

• OH → Slight ppt

• CO3 → white ppt

• SO₄ → Slight ppt

Ba

• OH → Soluble

• CO₃ → White ppt

• SO4 → insoluble white ppt

Test for sulfate

Ba → BaSO₄ → insoluble white ppt

Group 2 solubility trends hydroxides and sulfates

Hydroxides

• More soluble down group

Sulfates

• Less soluble down group

Thermal stability Carbonates and hydroxides

Increases down group

Halogen group 7 reactivity

Cl₂ > Br₂ > I₂

Decreases down group

Observations of halogen displacements

More reactive halogen displaces less reactive halide

NaCl + Br and I → no colour change

NaBr + Cl₂ → Colourless to pale yellow

NaI + Cl₂ or Br₂ → Colourless to brown

Halogen oxidising power trend

Decreases down group

• Weaker nucleus attraction of electrons

• Larger radius

Volatility of halogens

Decrease down group

Cl₂ gas

Br₂ liquid

I₂ Solid

Halide test

Dilute HNO₃ + AgNO₃

Cl → White

Br → Cream

I → Yellow

Halide test with NH₃

Cl → dissolves in dilute

Br → dissolves in conc

I→ does not dissolve

Flame test

Li⁺ → Crimson

Na⁺ → Yellow

K⁺ → lilac

Ca²⁺ → Brick red

Sr²⁺ → Red

Ba²⁺ → Apple green

Mg no colour change

Insoluble salt formation

Ba²⁺ + SO₄²⁺ → BaSO_⁴

Ionisation trends across period

Increase

• Nuclear charge increase

• Protons increase

• Shielding remains the same

• Stronger attraction electrostatic attraction between nucleus and electrons

• More energy to remove electron

Electronegativity across period

Increases

• Nuclear charge increases

• Atomic radius decrease

• Bonding electrons closer to nucleus

• Stronger attraction

Atomic radius across period

Decrease

• More protons → stronger nuclear attractions

• Electrons added to same shell same shielding

• Electrons pulled closer to nucleus

Identification with ppt

Sulfates

• Pb and barium → insoluble white ppt

Iodine

• Pb → yellow ppt

Carbonates

• White ppt with most

Colours of d block ions

Cr³⁺ → Green

CrO₄^2- → Yellow

Cr₂O₇^2- → Orange

MnO₄^- → Purple

Cu²⁺ → blue

Fe²⁺ → Pale green

Fe³⁺ → Brown

Co²⁺ → Pink

Why are transition metal ions coloured

d electron transitions due to splitting of d-orbitals

Copper 2+ and NH₃

Blue → Deep blue

[Cu(NH₃)₄(H₂O)₂]²⁺

Copper2+ and Cl^-

Blue → Yellow green

[CuCl₄]²⁺

Cobalt 2+ and Cl^-

Pink → Blue

[CoCl₄]^2-

Ligand complexes

[Cu(H₂O)₆]²⁺ → Pale blue (octahedral)

[Cu(NH₃)₄(H₂O)₂]²⁺ → Deep blue (octahedral)

[Co(H₂O)₆]²⁺ → Pink (octahedral)

[CuCl₄]²⁻ → Yellow-green (tetrahedral)

[CoCl₄]²⁻ → Blue (tetrahedral)

d block catalysts in process

Iron → Haber (N₂ + 3H₂ = 2NH₃)

Nickel → Hydrogenation of alkenes

V₂O₅ → Contact process

MnO₂ → Decomposition of H₂O₂

OH^- and dblock

Fe²⁺ → Green ppt

Fe²⁺ → brown ppt

Cu²⁺ → Blue ppt

Cr³⁺ → Green ppt → dissolves in excess

Redox titration for copper 2 ions equations

2Cu2⁺ + 4I^- → 2CuI(s)+ I₂

I₂ + 2S₂O₃^2- → 2I^- S₄O₆^2-

1 mol Cu²⁺ ≡ 1 mol S₂O₃²⁻

Redox copper 2 ions

• Excess KI to Cu2+ (blue) → cloudy brown solution

• Titrate brown I₂ with S₂O₃^2- → straw colour

• Starch indicator → blue black → flesh colour

HCl and CaCO₃

2HCl + CaCO₃ → CaCl₂ + CO₂ + H₂O

Apparatus measure HCl and CaCO₃

• Digital scale

• Weighing boat

• Spatula

• Stopwatch

• Clamp and stand

• 250cm3 conical flask

• Gas syringe delivery tube

• Measuring cylinder 50cm3

• Rubber stop

Wy must rubber stopper with delivery tube be placed on conical flask immediately

Reaction start straight away and co2 produced immediately

Avoid loosing too much

Weighing by difference technique

Accurately measure solid\

Weighed in weighing boat before added to acid and reweighed

Investigate effect of surface area on rate of reaction

CaCo3 and HCl

Hcl conc constant and change surface area grinding up into fine powder

Importance of constant temp in gas experiment

Affect volume of gas

Increase temp cause gas to expand → larger volume than should be

Initial rates method

Measuring initial rate of reaction with different concentrations

Iodine clock apparatus

Stopwatch

Measuring cylinders

Pipette safety filler

Burette and funnel

Stirrer

White tile

Iodine clock equations

H₂O₂ + 2H⁺ + 2I^- → I₂ + 2H₂O

Thiosulfate ions →

2S₂O₃^2- + I₁ → 2I^- + S₄O₆^2-

Control variables for iodine clock

Temperature of reactants

Volume of reactants (not H₂O₂ and water)

Concentrations of rest

Why is iodine clock on a white tile

Colourless to blue-black quickly and easily identified

Hazards with AgNO₃ HNO₃ HCl

AgNO₃ Corrosive

HNO₃ Corrosive

HCL irritant

Redox titration method of Fe2+

Fe2+ → Standard solution

Titrated known conc KMno4

Oxidising Fe2+ → Fe3=

Find mean titre → Moles of fe2+ → Mr

Standard solution apparatus

Solution with known concentration

• Weighing boat

• 250 volumetric flask

• digital scale

• funnel

• beaker pipette

Meniscus

Curved surface of liquid in tube

Make solution bottom of meniscus up to mark

Swirling in redox titration

Ensure all reacting particles collide and react

Accurate end point

Why rinse with reagents not water

Rinsing equipment remove water

Water will affect solution concentrations

More accurate

Dynamic equilibrium

Forward and reverse reactions occur at the same rate

Le Chatelier’s principle

System at equilibrium subjected to a change, shifts to minimise the effect of the change