C Unit 2.5 Hydrocarbons

Question 1

Well if u seem concerned, go see the first few pages if ya want

Answer 1

Okay

Question 2

U gotta, now or never

Answer 2

U right

Question 3

What are free radicals?

Answer 3

Atoms/groups of atoms which have a single unpaired electron

Question 4

How are free radicals formed?
What name for it?

Answer 4

Bond splits evenly - each atom having one of the 2 electrons
Homolytic fission

Question 5

What are the 3 stages of Homolytic fission?

Answer 5

Stage 1 - Initiation
Stage 2 - Propagation
Stage 3 - Termination

Question 6

Explain intitiation stage?

Answer 6

UV radiation causing a [chlorine-chlorine] bond to split homolytically

(symbol for radical is that full stop on the top right of it) aka

Cl]-[Cl (U.V)-> Cl˙ + Cl˙ OR Cl2 (UV)-> 2CL˙ (Chlorine radicals)

Question 7

Explain propagation stage?

Answer 7

Radicals = reactive ∴ take part in a series of propagation reactions

CH4 + Cl˙ -> ˙CH3 + HCl
CH3 + Cl2 -> CH3Cl + ˙Cl

There’s a diagram for dat one too + chain reaction type sh forming radical as a product

Question 8

Explain termination stage?

Answer 8

Cl˙ + Cl˙ -> Cl2
Cl˙ + ˙CH3 -> CH2Cl
˙CH3 + ˙CH3 -> CH3CH3

Propagation will continue until two radicals meet = termination

Question 9

How are alkenes more reactive than alkanes?

Answer 9

• Alkenes more electron density
• Due to more electrons as there are 2 electron pairs = 4 electrons
• Centred between carbons either side of double bond

Question 10

How can alkenes form bonds?

Answer 10

• Can use one electron pair in double bond
• To react and form new bonds to each carbon atom

Question 11

What happens to alkanes when their one electron pair is used?

Answer 11

• Sigma bond broken
• Molecule destroyed

Question 12

U also gotta look at page 6 for them reactivity of alkene n alkane n stuff

Answer 12

Okay

Question 13

Explain how alkenes give rise to pi bonds?
And ig what that means too?

Answer 13

In the carbon bond:
- As second bond (second pair of electrons) created
- Overlap of p-orbitals of the 2 carbon atoms take place
- Forms pi bonds (area of high electron density)
- Above and below plane of molecule

THAT’S WHY, it’s a double bond

Question 14

Or just go to page 7 for alkenes related bonding thing

Answer 14

Okay
skip skip skip skip

Question 15

What it mean for carbon-carbon double bonds having restricted rotation?

Answer 15

• No free rotation due to pi-bond
• Therefore even tho it’s the same molecules,
• It’s a different thing due to it’s position
• That’s why carbon-carbon single bonds would still have the same name despite different position of molecules

Question 16

Define electrophile?

Answer 16

Atom (or group of atoms) attracted to an electron-rich centre/atom. Accepts a pair of electrons to form new covalent bond

E.g. Hbr/HCl/Cl2/Br2/H

Question 17

Define nucleophile?

Answer 17

Chemical that can donate a pair of electrons with the subsequent formation of a covalent bond

E.g (All molecules except H have 2 dots above em, lone pair type sh)
-OH, Br-, Cl-, -CN/H2O or NH3

Question 18

Define free radical?

Answer 18

Atom/group of atoms with an unpaired electron

E.g. ˙Cl, ˙CH3, ˙CH2CH3

Question 19

What 2 types of addition reactions ig?

Answer 19

• Bromination
• Hydrogenation

Question 20

4 MAIN THINGS needed to be shown in the model diagram of a reaction between an alkene and some rando ahh molecule?
(4 things)

Answer 20

1. Curly arrows
2. Dipoles
3. Lone pairs
4. Charges (full)

MAKE SURE U LOOK AT THESE PAGES FOR EASY 4 MARKS

Question 21

Look at the page for beginning of section G - Electrophilic Addition. ,’:D

Answer 21

Yikes man…

Question 22

For bromination, test for what? and how to tell if certain thing present?

Answer 22

• Test for alkenes and presences of C=C double bonds
• Bromine water will decolourise if C=C present

Question 23

What’s hydrogenation as well?

Answer 23

• H added to alkenes, to saturate them
• Forms alkanes

Question 24

Explain how u know if it’s a carbocation?
And how u know which ones more stable?

Answer 24

• Propane? But there’s a positive ion? at the bottom of either Carbons.
  e.g. 1° - carbocation, 2° - carbocation, etc. lol
• 1° is more stable, 3° is less.
  Additionally, 1° - carbocation has that positive ion on the bottom right, 3rd carbon :v

Question 25

But in general how to tell which carbocation stable?

Answer 25

Uhhhh, more alkyl groups attached??? (CH3 or CH2CH3) - Alkyl groups donate electron density to carbocation, helps stabilise

Question 26

What u use to test for alkenes? How so?

Answer 26

- Potassium manganate(VII) solution - Cold state, colour depends based on acidic/alkaline conditions

Question 27

Show differences in potassium manganate(VII) solution based on acid/alkali

Answer 27

Acidified (dilute sulphuric acid) = Purple solution -> Colourless Alkaline (sodium carbonate solution) = Purple solution -> Dark green -> Dark brown precipitate

Question 28

What's the ick with potassium manganate(VII) solution tho?

Answer 28

- Could give same results from the alkaline solution It **may** contain a carbon-carbon double bond. But equally it could be any one of a large number of other compounds all of which can be oxidised by manganate(VII) ions under alkaline conditions

Question 29

Aye man, u gotta be aware of carbocations n stuff, like is the addition of HBr to propene n stuff, and u can tell if it's stable or not

Answer 29

Bruhhh

Question 30

What is addition polymerisation?

Answer 30

Addition reaction that continues until actively stopped Biology fr

Question 31

What can be used for monomers adding together toe form long chain polymers? (2 things)

Answer 31

- Alkenes - Substituted alkenes

Question 32

The polymer doesn't contain double bond, BUT, what is added to the name n stuff showing that it probably does?

Answer 32

- Poly added to monomer - To involve ene e.g. ethene -> polyethene

Question 33

Make sure u know how to draw a monomer, how to show it's a repeat unit?

Answer 33

Square brackets [LOL]

Question 34

***** Describe what happens to ethene molecules during the formation of polyethene (3 marks)

Answer 34

- Double bond breaks (1) - Electron pair forms a new covalent bond, on a carbon from a neighbouring (ethene) molecule (1) - Forming a saturated polymer chain (1)

Question 35

And ye, definitely look at the last page, and for sure, ya gotta do some exam questions

Answer 35

Okayyyy

Question 36

This guy is actually a fool

Answer 36

D: