paper three stuff

Question 1

Define a homologous series

Answer 1

A family of compounds with similar chemical properties and structures that are differentiated by a CH2 group

Question 2

What is the difference between a sigma and pi bond?

Answer 2

Sigma bond: The direct overlap of orbitals of each bonding atom

Pi bond: The sideways overlap of two adjacent p orbitals

Question 3

What is required for E/Z isomerism and Cis/Trans isomerism?

Answer 3

E/Z: A double bond and each bonded carbon much be attached to each carbon atom of the double bond

Cis/Trans: One of the attached groups must be the same for both groups

Question 4

Why is C-Cl have a higher bond enthalpy than C-I?

Answer 4

Because C-CL have a higher difference in electronegativity and a higher bond enthalpy than the bond in C-I

Question 5

How do chlorine radicals catalyse the breakdown of the ozone layer?

Answer 5

Cl* + O3 -> CLO* + O2
CLO* + O -> O2 + Cl*

O3 + O -> 2O2

Chlorine catalyse the breakdown of the ozone layer and stay in the atmosphere for a long time due to the strong halogen-carbon bonds

Question 6

How do you purify impure solids by recrystallisation?

Answer 6

1) Use minimum volume of HOT solvent to dissolve product
2) Use Bucher funnel and do reduced pressure filteration
3) Wash with a fresh cold solvent and leave on a dry paper towel to dry

Question 7

What are methods of finding out a purity or identity of a substance?

Answer 7

Determining melting point and comparing to a known data base, the more pure the substance the sharper and well defined melting point it will have.

Also could use thin layer chromatography and compare to the known pure sample

Spectroscopy techniques

Question 8

How do you obtain and purify an organic liquid?

Answer 8

Add alcohol and HCL into a separating funnel, place stopper, shake vigoursly and release pressure when required
Allow mixture to separate and collect bottom layer
Distill and collect impurities

Question 9

Why should water in a condenser be used from the bottom to the top?

Answer 9

Maximise heat transfer for condensation and prevent the water filling in incorrectly

Question 10

What is the equation for atom economy and how can you increase it?

Answer 10

Atom economy is : Mr of desired products/Mr of all products x 100
To increase atom economy, you can find uses for the waste products

Question 11

What does an M+1 peak indicate?

Answer 11

An isotope with a higher MR than the original element

Question 12

Why is phenol and alkenes more reactive than benzene?

Answer 12

Because Benzene has a delocalised system of Pi electrons with low electron density therefore is unable to polarise certain reactants such as halogens and haloalkanes.

Question 13

Describe the delocalised model of benzene

Answer 13

Adjacent p-orbitals overlap above and below the plane
Consists of a system of delocalised pi electrons
Overall low electron density

Question 14

What happens when a polyester goes through acid and alkaline hydrolysis?

Answer 14

Acid: Carboxylic acid and alcohol
Alkaline: Salt and Alcohol

Question 15

What happens when a polyamide goes through acid and alkaline hydrolysis?

Answer 15

Acid: NH3+ and carboxylic acid
Alkaline: Salt and amine, NH2

Question 16

How does TLC separate and identify compounds?

Answer 16

Based on the different affinities for the adsorbent during the stationary phase, the retention factor is calculated and compared against a pure sample or run against a pure sample

Question 17

What does gas chromatography depend on?

Answer 17

Gas chromatography depends on the solubility of the components during the liquid stationary phase.
The more soluble the the slower it will move and therefore lower the retention time

Question 18

What is the difference between structural isomers and steroisomers?

Answer 18

Structural isomers: The same molecular formulae but different structural formulae

Stereoisomers: Same structural formulae but different arrangements of atoms in a space

Question 19

What happens when you react an acyl chloride and a NH2 group?

Answer 19

Forms an amide

Question 20

How do you get from a haloalkane to NH2 group?

Answer 20

By adding ethanol and excess ammonia

Question 21

How do you get from a nitrile to a carboxylic acid?

Answer 21

Through aqueous acid hydrolysis

Question 22

How do you go from an alcohol to a haloalkane?

Answer 22

React with hydrogen halides that are formed in situ with an acid and a sodium halide.
For example H2SO4 and NaBr which will produce HBr that will react with the alcohol

Question 23

How would you purify a liquid distillate?

Answer 23

+ Add a neutralising agent such as Na2CO3
+ Dry with an anhydrous salt, e.g MgSO4
+ Redistill at 44*

Question 24

What are some limitations of organic synthesis involving radical substituion?

Answer 24

Substitution could occur at different points along the chain

Formation of unwanted products during termination

Question 25

How do you get from a carboxylic acid to an acyl chloride and what other products are produced?

Answer 25

Carboxylic acid + Thionyl chloride (SoCl2) makes an Acyl chloride and SO2 and 2HCL

Question 26

Why are mechanisms called heterolytic and homolytic FISSION

Answer 26

Involve the breaking of a covalent bond
Heterolytic: One of the bonding atom receives both of the bonding electrons
Homolytic: Each one of the bonding atoms receive an electron from bonding pair

Question 27

Why does C-F hydrolyse slower than C-CL?

What set up would you require to test this?

Answer 27

Because C-F has a higher bond enthalpy, therefore a stronger bond so therefore will take a slower time to hydrolyse.

Reflux set up, condenser with water and reflux pear shaped flask thing