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Chemistry A-Level Cheat Sheet (DRAFT) by

Things to remember/memorise for a-level chem, including both yr12 and yr13 topics. This is OCR A a-level chemistry.

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Transition metal complexes

Complex
Few drops NaOH/NH3
Excess NaOH
Excess NH3
pale green [Fe(H20)6]3+
dirty green Fe(OH)2
-
-
green/­violet [Cr(h206]3+
pale green Cr(OH)3
deep green soln. [Cr(OH)6]3+
violet soln. [Cr(NH3)6]3+
yellow [Fe(H2O)6]3+
brown Fe(OH)2
-
-
blue [Cu(H2O)6]2+
pale blue Cu(OH)2
-
deep blue soln. [Cu(NH­3)4­(H2O)2]2+
pale pink [Mn(H2O)6]2+
light brown Mn(OH)2
-
-

Test for halide ions

Halide ion
Adding HNO3 and AgNO3
Adding NH3
Chloride
White ppt
Dissolves in dilute
Bromide
Cream ppt
Dissolves in conc.
Iodide
Yellow ppt
Doesn't dissolve
HNO3 added first to the halide, then AgNO3. This forms a ppt, from which the colour can be used to identify the halide. NH3 is then added if necessary; in dilute ammonia, e.g: only chloride ions dissolves, whereas iodide ions don't dissolve at all.

Organic tests (AS)

Alcohols
Add K2Cr2O7/H+
Orange to green for 1st and 2nd alcohols
Alkenes
Add bromine water
Orange to colourless
Haloal­kanes
Dissolve in ethanol, add water, then do the halide test

Organic tests (A-level)

Aldehy­de/­ketone
Add 2,4-DNP (Brady's reagent)
Orange ppt forms
Aldehyde
Add Tollen's reagent
Siler mirror forms
 
Add Fehling's reagent
Red ppt forms
Carboxylic acid
Add carbonate (same as AS)
CO2 forms
 
Add PCl5
Steamy white fumes produced
Benzne
Add bromine water (room temp)
no reaction.
 
Combustion
Burns with sooty flame

Radical Substi­tution

Conditions
UV light
Bond fission
homolytic (2 radicals formed from covalent bond)
Organic product
haloalkane
Limita­tions
further substi­tution is almost impossible to control, products have to be separated by fractional distil­lation or chroma­tog­raphy
INITIATION
Cl2 -> 2Cl*
PROPOG­ATION
CH4 + Cl* -> *CH3 + HCl
 
*CH3 + Cl2 -> CH3Cl + Cl*
TERMIN­ATION
2Cl* -> Cl2
 
*CH3 +*CH3 -> C2H6
 
*CH3 +Cl* -> CH3Cl

Electr­ophilic Substi­tution (nitration of benzene)

Reagen­ts/­con­ditions
conc. HNO3, conc. H2SO4, 50*C
Electr­ophile
NO2+
Organic product
nitrob­enzene
Gen. of electr­phile
HNO3 + H2SO4 -> NO2+ + HSO4_ + H2O
Regen. of catalyst
HSO4_ + H+ -> H2SO4

Electr­ophilic Sub. (chlor­ination of benzene)

Reagen­ts/­con­ditions
Cl2, AlCl3
Electr­ophile
Cl+
Organic product
chloro­benzene
Gen. of electr­phile
AlCl3 + Cl2 -> AlCl4- + Cl+
Regen. of catalyst
AlCl4- + H+ -> AlCl3 + HCl

Electr­ophilic Sub. (acylation of benzene)

Reagen­ts/­con­ditions
CH3COCl, AlCl3
Electr­ophile
CH3CO+
Organic product
phenyl ethanone
Gen. of electr­phile
AlCl3 + CH3COCl -> AlCl4- + CH3CO+
Regen. of catalyst
AlCl4- + H+ -> AlCl3 + HCl

Electr­ophilic Sub. (alkyl­ation of benzene)

Reagen­ts/­con­ditions
CH3Cl, AlCl3
Electr­ophile
CH3+
Organic product
methyl benzene
Gen. of electr­phile
CH3Cl + AlCl3 -> CH3+ + AlCl4-
Regen. of catalyst
AlCl4- + H+ -> AlCl3 + HCl

Electr­ophilic Sub. (bromi­nation of benzene)

Reagen­ts/­con­ditions
Br2, AlBr3
Electr­ophile
Br+
Organic product
bromob­enzene
Gen. of electr­phile
AlBr3 + Br2 -> AlBr4- + Br+
Regen. of catalyst
AlBr4_ + H+ -> AlBr3 + HBr
 

Ammonium, NH4+

Add NaOH to test for NH3
Red litmus paper turns blue if present

Carbonate, CO3^2-

Add HCl to carbonate solution
CO2 forms. Turns limewater cloudy

Sulphate, SO4^2-

Add BaCl2
White ppt forms if present (BaSO4)

Rate equations

Rate = k[A]m[B]n

k = Ae-Ea/RT
ln k = -Ea/RT + ln A

k = rate constant
[A] = concen­tration of A
[B] = concen­tration of B
m = order wrt A
n = order wrt B
A = Arrhenius pre-ex­pon­ential factor
e = expone­ntial
Ea = activation energy (kJmol-1)
T = temper­ature, K
R = gas constant (8.314 JK-1mol-1)
ln = natural log

Reaction pathways (aliphatic compounds)

Conditions and reacta­nts­/re­agents shown

Electr­ophilic Addition (alkenes)

Electr­ophile
electron pair acceptor
Carboc­ation
positive ion with electron deficient carbon
Bond fission
hetero­lytic (cation and anion formed from covalent bond)
Organic product
haloalkane
! Curly arrows show movement of an electron

Nucleo­philic Substi­tution (haloa­lkanes)

Reaction
Reagen­t/c­ond­itions
Nucleo­phile
Organic product
Hydrolysis (NaOH)
hot NaOH(aq)
OH
alcohol
NH3
ethanolic NH3
-
amine
KCN
ethanolic KCN
-
nitrile
Nucleo­phile: electron pair donor
Substi­tution: when an atom or group of atoms is replaced by another
Ethanolic: derived from or containing ethanol

Nucleo­philic Addition (carbonyl compounds)

Reaction with NaBH4
Reagen­ts/­con­ditions
NaBH4, warmed
Reaction type
reduction
Nuceophile
H-
Organic product
alcohol
Reaction with HCN
Reagen­ts/­con­ditions
HCN
Nucleo­phile
CN-
Organic product
hydrox­yni­trile

Free radical sub. of ozone

Depletion 1*
CFCl3 --UV-> CFCl2* + Cl*
Cl* + O3 -> ClO* + O2
ClO* + O -> Cl* + O2
Depletion 2**
N2 + O2 -> 2NO*
NO* + O3 -> NO2* + O2
NO2* + O -> NO* + O2
*due to chlorine radicals from CFC's
**due to nitrogen oxide from aircraft engines and lightning