organic chemistry

Question 1

Define isomer

Answer 1

Molecules that have the same molecular formulas

Question 2

Define structural isomer

Answer 2

Same molecular formula but different structural formula

Question 3

Define positional isomer. What is the positional isomer of pent-1-ene?

Answer 3

The functional group is attached to different points in the chain. Pent-2-ene

Question 4

Define chain isomer. What are the chain isomers of 1-chlorobutane?

Answer 4

. Changes to the hydrocarbon chain. 1-chloro (2-)methyl propane

Question 5

Define functional group isomer. What are the 2 pairs of functional groups that show functional group isomerism?

Answer 5

same molecular formula but different functional group. Alkene&cycloalkanes. Aldehydes&ketones.

10. Cyclobutane. Pentanal.

Question 6

Define stereoisomers

Answer 6

Same structural formula but different 3D arrangement of atoms.

Question 7

Define E/Z isomers

Answer 7

E/Z isomers have high priority groups attached to same side (Z isomers) or different sides (E isomers) of the C=C bond

Question 8

What are the 2 things that molecules must have to show E/Z isomerism?

Answer 8

C=C bond and two different groups attached to each carbon of C=C .

Question 9

What are the general formulas of alkanes and alkenes?

Answer 9

Alkanes = CnH2n+2 Alkenes = CnH2n

Question 10

What is crude oil? Describe how crude oil is separated into fractions.

Answer 10

A mixture of different length hydrocarbons. Fractional distillation

Question 11

What are the properties of the shorter fractions?

Answer 11

Lower boiling points, flammable, volatile, easy to ignite

Question 12

Explain why longer hydrocarbons have higher boiling points.

Answer 12

They have stronger Van Der Waal forces between their molecules

Question 13

How does the boiling point of hydrocarbons, that are straight and branched chain isomers, compare? Explain your answer

Answer 13

Straight chains have higher boiling points because they have stronger Van Der Waal forces between their molecules

Question 14

Why is cracking necessary? Give the conditions and products formed for thermal and catalytic cracking.

Answer 14

cracking meets the demand for stronger alkanes to use as fuels. Thermal cracking = 900C, 70atm, makes alkanes and alkenes. Catalytic cracking = 450C, 1-2atm, zeolite catalyst, makes aromatic alkanes

Question 15

Complete this cracking equation: C12H26 → C8H18 + 2 _________

Answer 15

C12H26 à C8H18 + 2C2H4

Question 16

Write one equation for the complete combustion of hexane and two equations for the incomplete combustion of hexane

Answer 16

C6H14 + 9.5O2 à 6CO2 + 7H2O, C6H14 + 6.5O2 à 6CO +7H2O, C6H14 + 3.5O2 à 6C + 7H2O

Question 17

Name the greenhouse gases. Explain how they cause global warming

Answer 17

O2, CH4 and H2O. Short wave radiation from the sun can travel through them to reach the Earth. The Earth absorbs this radiation and remits it as longer length radiation. This longer length radiation cannot travel through the greenhouse gases so stays in the atmosphere warming the Earth.

Question 18

In what circumstances are nitrogen monoxide and nitrogen dioxide formed? Write an equation to show how nitric acid, that causes acid rain, is formed.

Answer 18

In car engines, the very high heat causes the nitrogen and oxygen in the air to react together.

Question 19

In what circumstances are nitrogen monoxide and nitrogen dioxide formed? Write an equation to show how nitric acid, that causes acid rain, is formed

Answer 19

N2(g) + O2(g) → 2NO(g), 2NO(g) + O2(g) → 2NO2(g)

4NO2(g) + 2H2O(l) + O2(g) → 4HNO3(aq)

Question 20

In what circumstances are sulfur monoxide and sulfur dioxide formed? Write equations to show how sulfuric acid, that causes acid rain, is formed.

Question 21

What does flue gas desulfurisation mean? Write two equations to show the reactions that occur.

Answer 21

Removing sulfur dioxide from power station fumes. CaO + SO2 ® CaSO3

CaCO3 + SO2 ® CaSO3 + CO2

Question 22

What are the catalysts inside a catalytic converter? Write an equation to show the reaction that occurs.

Answer 22

Platinum, palladium and rhodium. 2NO2 + 2CO à 2CO2 + N2

Question 23

describe heterolytic and homolytic fission.

Answer 23

heterolytic fission – breaking a covalent bond so one atom gets a lone pair of electrons. Homolytic fission – breaking a covalent bond so each atom gets one unpaired electron (is a free radical)

Question 24

What are the names of the 3 steps in the free radical substitution mechanism?

Answer 24

Initiation, propagation, termination

Question 25

Write a balance equation for the following: ethane + bromine à 1,2-dibromoethane + hydrogen bromide

Answer 25

2Br2 + CH3CH3 à CH2BrCH2Br + 2HBr

Question 26

Write initiation, propagation and termination equations for the whole free radical substitution mechanism of chlorine reacting with ethane to produce chloroethane.

Question 27

chemist wants to produce a high proportion of chloroethane in the reaction above. What ratios of chlorine and ethane should she start with?

Answer 27

Higher ratio of ethane to chlorine

Question 28

What are chlorofluorocarbons? How were they used in the past? What negative effect on the environment do they have?

Answer 28

Halogenalkanes where all hydrogens have been replaced by Cl or F. They were used as an inert gas in aerosols/fridges/fire extinguishers. In the upper atmosphere they break down to produce chlorine free radicals, these destroy the ozone layer.

Question 29

Why are only chlorine free radicals formed from chlorofluorocarbons?

Answer 29

The C-Cl bond has a lower bond enthalpy (is weaker) than the C-F bond.

Question 30

write two equations to show how chlorine free radicals catalyse the breakdown of ozone. Then write an overall equation that represents this process.

Answer 30

Cl* + O3 → ClO* + O2

ClO* + O3 → 2O2 + Cl*