Alevel AS化学考前最后20题！（附答案解析）

明天就要进行 AS化学 22 卷（CAIE考试局）的考试了，老师根据往年的出题规律，给大家出了考前最后 20 题，来看看这些题你是否能回答出来！

Physical Chem

1. Explain the observed trend in first ionisation energies down Group[3]Down the group first ionisation energies decrease. More shielding, and distance between nucleus and outer electron increase, weaker nuclear attraction.

2. Explain the observed trend in first ionisation energies across a period[3] Across a period first ionisation energies increase. Similar shielding, and more nuclear charge, lead to stronger nuclear attraction.

3. Explain why aluminium(group13) has a lower first ionisation energy than
magnesium(group2). [2] Al has one more 3p orbital than Mg, so electron removed from higher energy leveland more distance. Thus, less energy needed to remove electron and less nuclearattraction.

4. Explain why sulfur(group16) has a lower first ionisation energy than
phosphorus(group15). [2] S has one more electron pair causing electron spin-pair repulsion, less energyneeded to remove electron.

5. Copper has a melting point of 1085°C and a high electrical conductivity. Explain
these properties of copper by referring to its structure and bonding. [2] Copper has strong metallic bonds so the melting point is very high. There aredelocalised electrons which are free to move throughout the giant structure toconduct electricity.

Environmental Protection

6. Explain how uncontrolled use of nitrate fertilisers can cause problems. [3]Explosion of algal(藻类) growth(必写), sunlight is blocked out, preventing photosynthesis, decreasing concentration of oxygen in water(必写).

7. Extra supplementary Tips Photochemical smog: nitrogen oxides+ unburnt hydrocarbon→PAN(ultraviolet light) Acid rain: SO2 + NO2→NO+SO3 2NO+O2→2NO2 Burn fossil fuels

8. uses Nitrogen-containing substance: fertilizer Calcium-containing alkaline substances: lowering the pH of acidic soil.

Inorganic Chem

9. Explain the differences in observations, at room temperature, when NaI(s) reactswith concentrated sulfuric acid compared to those for NaCl(s).Iodide ions are stronger reducing agents than chloride. iodide ion can beoxidised but chloride cannot be oxidised by H2SO4. So NaI will form I2 purple gas.

10. State and explain the relative thermal stabilities of the hydrogen halides, HX. [2] Thermal stabilities of the hydrogen halides decrease down the group. Bondenergy of H-X decrease due to bond length increase.

Organic Chem

11. Explain why but-2-ene shows geometrical isomerism. [2]Each carbon of carbon-carbon double bond bonded with two different groups. carbon-carbon double bond cannot rotate.

12. Why does CH3CH(Cl)COOH have optical isomerism . It has chiral carbon with four different groups. The mirror images is nonsuperimposable(不可重叠).

13. Explain why 2-bromo-2-methylpropane is the major product of this reaction. [2] The intermediate is tertiary carbocation which is more stable due to positiveinductive effect and more alkyl groups. This alkyl groups can reduce charge density of carbocation. (3 marks)

14. What does sp2hybridization mean? The overlap of an s orbit and two p orbits

Drawing

15. hydrogen bond

考前押题！AS化学考前最后20题！（附答案解析）