Chemistry Unit 3 Edexcel (AS LEVEL) Notes

CHEMISTRY UNIT 3 REVISION FLAME TESTS (1) Add HCl to solid sample; this forms a salt (2) Dip nichrome wire into sample with HCl (3) Hold wire/salt into bunsen flame

PRECIPITATION REACTIONS (1) Add nitric acid; remove impurities/neut. OH (2) Add AgNO3; makes silver halide (AgX) (3) Add NH3 (Ammonia) Solution (4) Sunlight + 2AgX; darkens to make 2Ag &

HALIDE SALTS & SULPHURIC ACID - in all reactions; forms HX (hydrogen halide) - observation: steamy fumes (NH3:white smoke KF + H2SO4 —> KHSO4 + HF KCl + H2SO4 —> KHSO4 + HCl F/Cl n/a 4 —> KHSO4 + steamy KBr + H2SO HBr fumes (HCl)

2HBr + H2SO4 —> SO2 + Br2 +2H2O

Br

reduces to SO2

steamy fumes (HBr) + brown gas (Br2)

I

reduces to S and

purple vapour (I2) +

DISPLACEMENT REACTIONS - more reactive halogen displaces less reactive halide ion from their compound

- Cl>Br>I - changes clear w/ organic solvent (2 layers Cl2 + KBr (solution) = orange solution (Br2) +∆H (bond breaking) vs -∆H (bond making)

CARBONATE/NITRATE THERMAL STABILITY - thermal stability increases down a group; group 2 is less thermally stable than group 1

- larger cations (more shielding/shells) - therefore, less polarising effect/distortion - therefore more stable

HYDROGEN - burning splint; squeaky pop OXYGEN - burnt splint; relights CO2 - pass thru limewater; goes milky white NITROGEN DIOXIDE - brown gas evolved; blue litmus —> red SULPHATE - add HCl and BaCl2; forms white ppt. of BaSO4 SULPHITE - add HCL/H2SO4 - sulphur dioxide produced SULPHUR DIOXIDE - add K2Cr2O7; goes orange -> green AMMONIA - turns blue litmus red (remember; its toxic - use fume cup) AMMONIUM (NH4+) - add NaOh; turns blue litmus red (forms NH3) HCl - steamy fumes produced; ammonia on glass rod - white smoke CHLORINE - bleaches litmus; KBr red —> brown (Br2 made) BROMINE - add to KI; goes from colourless ——> red/brown (I2) IODINE - starch indicator; turns dark blue (if iodine present) WATER - copper cobalt paper blue —> pink C=C BOND - bromine water; turns brown —> colourless NITRATE - add NaOH and Devarda’s Alloy; makes NH3 (red lit > blue) CARBONATE - add HCl; releases CO2 // or heat; decomp; oxide/CO2 REFLUX: organic compounds vapor condense back to reaction vessel - r.o.r for organic compounds slow; reflux heats without losing product - round bottom flask; reflux condenser with open tap; H20 in at bottom - use electric heater as ethanol/vapour can be flammable - ensure H2O is in at bottom; ensure full condenser w/ no air bubbles DISTILLATION - used to separate desired product from mixture - round bottomed flask, still head w thermometer (head at opposite end of condenser), reflux condenser and heater (electric) - vapour that is ±2℃ from b.p. is condensed + collected in beaker - cool flask in H2O; so flammable liquid doesn't escape + vig. reaction - NaHCO3; used to neutralize acid; shake in a separating funnel - in separating funnel; open tap and run off bottom/top layers after - magnesium sulfate/calcium chloride are drying agents; remove H2O TITRATIONS - use to fnd the conc. of unknown solution; one known - rinse pipette with solution and discard rinsings; use fller to fll to mark - discharge pipette into conical flask; touch end of pipette onto surface - rinse burette w/ other solution & discard rinsings; funnel to fll HALOGENOALKANES - add NaOH (aq), nitric acid and AgNO3 1o ALCOHOL - distillation to ALDEHYDE +[O], reflux to CARB. ACID 2o ALCOHOL - same as above, forms KETONES 3o ALCOHOL - cannot be oxidized therefore remains same !!!! 3o HALOGENOALKANES react fastest; due to SN1 vs SN2

- incomplete combustion (soot); less energy - beaker absorbs heat/alcohol evap; less nrg - assumption of density/s.h.c of water Improvements - add lid to beaker or cup

HALOGENOALKANE - AQ ALKALI - react w/ aqueous alkali (e.g. NaOH)

- halogen substituted by OH - forms alcohol - called hydrolysis/nucleophilic sub. - fluoro least reactive; high bond ∆H HALOGENOALKANE - AMMONIA - reacts w ammonia to make amine

- amine is -NH2/-NH/-N-group - is example of nucleophilic sub. HALOGENOALKANE SAFETY and PRECAUTIONS ALCOHOLIC Toxic - use gloves & fume cupboard Flammable - use water bath, no flame Harmful gases - use fume cupboard Corrosive wear googles and MELTING -POINT DETERMINATION - sharp bp. over small range - pure YIELDS NEVER 100% - transfer losses [loss during purifc.]

- competing reactions carbon dioxide dissolves in H2O -MAKE UP 100CM3 OF SOLUTION

- discard rinsings; make up to mark - shake/mix/invert

FEHLINGS/BENEDICTS SOLUTION - blue -> red w/ aldehyde (blue, ket.)

- deep blue Cu2+ complex, reduced to red Cu2O TOLLENTS REAGENT MAKING SALT SOLUTION add salt to water until it doesn't dissolve TYPES OF REAGENTS - add salt in excess Nucleophiles and allow to cool afterwards - heat - electron pair donators

- attack +ve ion or δ+ with lone pair

[g1 nitrate] decomp. to nitrite NO2)CALCULATIONS & oxygen (O2) ENTHALPY CHANCE [g2 q=mc nitrate] (1) ∆t (kJ) (2) fnd n (mol) (3) ∆H=q/n -1 Li) decomp. nitrite oxygen (incl. g1 include sign&and unit (kJmol - be suretotooxide, ) [g1 carbonate] Common Errors

- heat loss due to apparatus; no lid/insulation

USEFUL CHARGES Ag+ MNO4CO322+ Zn HCO3 SO423+ Al NO3 SO32NH4+ OHCR2O7222O S PO43-

Electrophile - species (δ+) that accepts

TYPES OF REACTIONS aldehyde - cho carb. acid large - cooh Addition - join two or more molecules to form one single ketone - =o (100AE) Polymerisation - join many simple monomer units to make polymer Elimination - when a small group of atoms breaks from larger molecule Substitution - when one species replaced by another Hydrolysis - split molecule into 2 new molecules (add H+ and OH-)

electrons - attracted to electron rich area (c=c) Free Radicals - highly reactive single atoms (-) with and unpaired electron. BOND FISSION Heterolytic - bond breaks unevenly;