2022年1月 ALevel化学考试时间
第一单元：1月12日
第二单元：1月17日
第三单元：1月24日
第四单元：1月7日
第五单元：1月14日
第六单元：1月20日
距离第一门化学考试还剩3天！
今天带大家复习AS化学，第一单元、第二单元涉及到的化学反应方程式。
第一单元
▄ Alkanes – with O2
Complete combustion：CH4 + 2O2 → CO2 + 2H2O
Incomplete combustion：CH4 + 1.5O2 →CO + 2H2O
▄ Alkanes – with Cl2, UV
CH4 + Cl2 → CH3Cl + HCl
Mechanism：Photochemical free radical substitution.
▄ Alkanes – improving the quality of fuels
Catalytic Cracking：C10H22 → C5H12 + C5H10
Conditions – Heat (600oC), Al2O3
Isomerisation
Reformation
▄ Alkenes – with H2
H2C=CH2 + H2 →CH3CH3
Conditions - Heat, Ni
▄ Alkenes – with Br2
CH3CH=CH2 + Br2→CH3CHBrCH2Br
Colour change (orange to colourless)
Mechanism：Electrophilic Addition
▄ Alkenes – with Bromine water
CH3CH=CH2 + Br2 / H2O →CH3CHOHCH2Br
Colour change (orange to colourless)
Mechanism：Electrophilic Addition
▄ Alkenes – with HBr/dry/gas
CH3CH=CH2 + HBr →CH3CH2BrCH3
Major product Mechanism ：Electrophilic Addition
Explanation for major product：Secondary carbocationic intermediate is more stable than primary.
▄ Alkenes – with KMnO4 / H2SO4
CH3CH=CH2 + [O] →CH3CHOHCH2OH
Colour change (purple to colourless – H2SO4)
Alkenes- Polymerisation
Unit 2
▄ Group 2 metals – with H2O
Mg：Mg + H2O → MgO + H2 (steam only)
Ca,Sr,Ba：Ca + 2H2O→ Ca(OH)2 + H2
▄ Group 2 metals – with O2
2Mg + O2 →2MgO
▄ Group 2 metals – with Cl2
Mg + Cl2 →MgCl2
▄ Group 2 Oxides – with H2O
MgO + H2O →Mg(OH)2
▄ Group 2 Oxides – with acids
MgO + H2SO4→ MgSO4 + H2O
▄ Thermal stability
Group 1 Carbonates：All stable to heat except for Li2CO3
Group 2 Carbonates：MgCO3→ MgO + CO2
Group 1 Nitrates
Li: 2LiNO3 → Li2O + 2NO2 + ?O2
Na, K, Rb, Cs ：NaNO3→NaNO2 + ?O2
? Group 2 – Nitrates
Mg(NO3)2→ MgO + 2NO2 + ?O2
▄ Solubility
Group 1 and 2 Sulphates
Decreases down the group - BaSO4 is insolubl
Group 1 and 2 Hydroxides
Increases down the group - Mg(OH)2 is insoluble
▄ Group 7 elements – with H2O
Cl2 + H2O→HCl + HClO
▄ Group 7 elements – with NaOH
In Cold Dilute Alkali: Cl2 + 2OH- →Cl- + ClO- + H2O Reaction type - Disproportionation
In Hot Conc. Alkali: 3Cl2 + 6OH- → ClO3- + 5Cl- + 3H2O Reaction type - Disproportionation
▄ Group 7 – Displacement reactions
Cl2(g) + 2Br-(aq) → Br2(aq) + 2Cl-(aq)
Observations：Green gas → orange solution
▄ Halide ions – with conc H2SO4：
NaCl(s) + H2SO4 →NaHSO4(s) + HCl(g)
Observations：Steamy white fumes
NaBr(s) + H2SO4→NaHSO4(s) + HBr(g)
2HBr(g) + H2SO4 → Br2(g) + SO2(g) + 2H2O(l)
Observations Steamy white fumes and orange fumes
NaI(s) + H2SO4→Products HI(g), I2(g) + H2S(g)
NaI(s) + H2SO4→NaHSO4(s)+HI(g)
Followed by oxidation of HI(g):
2HI(g)+H2SO4→I2(g) + SO2(g)+2H2O(l)
And:
6HI(g)+ H2SO4→3I2(g)+S(s)+4H2O(l)
And:
8HI(g)+ H2SO4→4I2(g)+ H2S(g) +4H2O(l)
Observations：Steamy white fumes and purple fumes
▄ Test for halide ions
Ag+(aq) + Cl-(aq) →AgCl(s)
Observations： White ppt – soluble in dilute ammonia
▄ Halogenoalkanes - with aqueous OH-
CH3CH2Br + OH-→ CH3CH2OH + Br-
Mechanism : Nucleophilic substitution (Sn1 or Sn2)
▄ Halogenoalkanes with ethanolic OH-
CH3CH2Br + OH-→H2C=CH2 + Br- + H2O
Mechanism: Elimination
▄ Halogenoalkanes - with CN-
CH3CH2Br + CN-→CH3CH2CN + Br-
Mechanism: Nucleophilic substitution
▄ Halogenoalkanes - with aqueous silver nitrate
CH3CH2Br + H2O + Ag+→ CH3CH2OH + AgBr
Fastest halogenoalkane :Iodo
Explanation: C-I bond is weaker than C-Br and C-Cl
▄ Halogenoalkanes - with NH3
CH3CH2Br + NH3→CH3CH2NH2 + HBr
Conditions： Conc NH3 / heat / closed vessel
▄ Preparation of halogenoalkanes
①Chloroalkanes from alcohols :
CH3CH2OH + Cl- → CH3CH2Cl + OH-
Conditions： H2SO4 / NaCl / heat
②Bromoalkanes from alcohols:
CH3CH2OH + Br-→CH3CH2Br + OH-
Conditions： NaBr / H3PO4 / Heat
Not H2SO4 / NaBr / heat as Br2 will form
③Iodoalkanes from alcohols:
CH3CH2OH + I- → CH3CH2I + OH-
Conditions： PI3 or P / I2
Not H2SO4 / NaI / heat as I2 will form
▄ Alcohols – 1o Partial Oxidation:
CH3CH2OH + [O] →CH3CHO + H2O
Conditions： Distil product as it is formed
▄ Alcohols – 1o Complete Oxidation:
CH3CH2OH + 2[O] →CH3CO2H + H2O
Conditions: Heating under reflux
▄ Alcohols – 2o Oxidation:
CH3CHOHCH3 + [O] →CH3COCH3 + H2O
▄ Alcohols – Dehydration:
CH3CH2OH→ H2C=CH2 + H2O
Conditions: Heating under reflux / NaOH – Aqueous
▄ Alcohols – Reaction with sodium:
CH3CH2OH + Na →CH3CH2O-Na+ + H2
Observation： Colourless effervescence 更多详情咨询老师即可~
