C6.2 Organic Chemistry Flashcards by Deleted Deleted

Hydrocarbons

Compounds that only contain hydrogen atoms and carbon atoms
Release carbon dioxide when burnt
Example: coal

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Alkanes

Hydrocarbons
Saturated - each carbon is bonded to another carbon by a single covalent bond
General formula CₙH₂ₙ₊₂
Names ending in “ane”

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First 5 alkanes

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How many bonds can carbon atoms form

Up to 4

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How many bonds can hydrogen atoms form

Only 1

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How alkanes react

Combustion when alkanes react with oxygen in the air and burn
If plentiful supply of oxygen or air complete combustion happens:
carbon atoms oxidised to carbon dioxide, hydrogen atoms are oxidised to water
Example: propane + oxygen -> carbon dioxide + water

If poor supply of oxygen or air incomplete combustion happens instead
alkane + oxygen → carbon monoxide (CO) + water

problem because carbon monoxide is toxic gas and can cause suffocation
Some carbon atoms may not be oxidised at all and released as carbon particles.
CLEAN FLAME PRODUCED

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Alkenes

Hydrocarbons
Unsaturated: Contain a carbon - carbon double covalent bond, C=C that can open up in reactions and bond
General formula CₙH₂ₙ

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First 4 alkenes

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How alkenes react

alkenes can burn in oxygen or air, and the products of combustion are the same as alkanes
SMOKY DIRTY FLAME PRODUCED
alkenes have a functional group allowing them to take part in wider range of reactions
C=C is the functional group - lets alkenes undergo addition reactions where double carbon bond opens up

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Addition reactions (polymerisation of alkene monomers)

atom or group of atoms combines with a molecule to form larger molecule, with no other product.
alkenes react with bromine in addition reactions forming colourless ‘dibromo’ compounds as they are unsaturated and C=C bond can open up but alkanes cannot as they are saturated with no C=C double bond

alkene + bromine → saturated, colourless dibromo-alkane compound
Example: Ethene + bromine -> dibromoethane The alkene decolourises bromine water that can be used
. to test for saturation
. C2H4 + Br2 -> C2H4Br2
. H H H H
. | | | |
H-C=C-H + Br-Br -> H-C-C-H
. | |
. Br Br

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How can an alkene become an alkane

Hydrogenation - Undergo addition reactions with hydrogen in presence of nickel catalyst
Example: Ethene + hydrogen -> ethane
. C2H4 + H2 -> C2H6
C=C carbon double bond opens up to react

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Alcohols in chemistry

Functional group: -OH (hydroxyl group)
General formula: CₙH₂ₙ₊₁OH

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First 5 alcohols

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Oxidation of alcohols
(by potassium manganate)

alcohol + oxidising agent → carboxylic acid

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Carboxylic acid

general formula CₙH₂ₙ₊₁COOH
functional group: -COOH (carboxyl)
Made by adding acidified (with H₂SO₄) potassium manganate solution to alcohol and warming with water bath
Colour change from purple to very pale pink as manganate ions are reduced to manganese atoms

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reactions of carboxylic acids

same as any weak acid:
Carboxylic acid + metal -> salt + hydrogen

Carboxylic acid + base -> salt + water

Carboxylic acid + carbonates -> salt + water + carbon dioxide

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Crude oil formation

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Remains of marine organisms / organic material buried under sea bed over millions of years under high temperatures and pressures
Finite resource
Separated by fractional distillation as larger molecules have higher boiling points,
due to stronger intermolecular forces

Order of crude oil fractions (top to bottom of column)

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LPG, petrol, paraffin, diesel, heating oil, fuel oil, bitumen

Cracking (chemistry)

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long alkane → smaller alkane + alkene

600-700⁰C
Alumina or silica catalyst

Conditions for addition polymerisation

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High pressure
Catalyst

DNA polymer

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Monomers are nucleotides (strands joined by hydrogen bonding)

Protein polymer

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Amino acids, each with functional group at each end (amine / amino group NH₂ and carboxyl COOH)
Amino acid structure:
. HH O
. | | ||
H-N-C-C-O-H
. |
. R

carbohydrate polymer

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starch, polymer of simple sugars like glucose

carboxylic acid + alcohol reaction

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carboxylic acid + alcohol → ester + water

condensation (organic chemistry)

2 molecules react to form 1 large molecule and 1 smaller (often water)

What are polyesters made from

Dicarboxylic acids and dialcohols They are condensation polymers Functional group: -COO-

What are polyamides made from

Dicarboxylic acids & diamines Contain amide functional group (CONH)

conditions for condensation polymerisation

without a catalyst at room temperature and pressure

Chemical cells

Exothermic reactions produce a potential difference between the two ends When one reactant is used up, cell goes flat

Daniell cell

Wet cell the negative electrode (zinc in the Daniell cell, whilst copper is the positive one)

Fuel cell anode half equation

2H₂ (g) → 4H⁺ (aq) + 4e⁻ Redox reaction

proton exchange membrane

where hydrogen ions travel through to cathode, whilst electrons travel through external circuit

Fuel cell cathode equation

4H⁺ (aq) + O₂ (g) + 4e⁻ → 2H₂O (g) Redox reaction

First 5 carboxylic acids

. O . || Methanoic acid: HCOOH: H-C-O-H . H O . | || Ethanoic acid: CH3COOH: H-C-C-O-H Propanoic acid: C2H5COOH Butanoic acid: C3H7COOH

How do alcohols react

Burn in the air with oxygen - combustion, or incomplete combustion if lack of oxygen Alcohol + oxygen -> carbon dioxide + water (complete combustion) Alcohol + oxygen -> carbon monoxide + water (incomplete combustion) Hydroxyl functional group lets alcohols undergo reactions other than combustion eg. they can be oxidised to form carboxylic acids. Other atoms in alcohol molecules usually do not take part in these reactions

Repeating units for addition polymers

1) Draw the monomer with bonds at 90°, if this is not given to you: H HH H H | | | | | C=C-C-H -> C=C | | | | H H H CH3 2) Redraw the monomer but: change double bond to single bond and draw two long bonds either side of where the double bond was put square brackets round the diagram, passing through the outer bonds ._ H H _ | | | | +—C-C——+ |_ | | _| n n used here to show that the unit repeats n times . H CH3

How is nylon formed

2 monomers needed: AMIDE group, CARBOXYLIC group Chemicals used: diaminohexane + dicarboxyllic acid Nylon forms at interface between liquids - don’t mix Wind it using a taper

Why petrol has a lower boiling point than diesel?

Petrol molecules are smaller than diesel molecules Weak intermolecular forces between petrol molecules compared to diesel molecules so less energy needed to boil

Addition polymerisation vs condensation polymerisation

Addition: 1 product (the polymer), 1 monomer Condensation: 2 products (polymer and a small molecule like water), 2 monomers (unless amino acids)

Fuel cell

Cell supplied with a fuel and oxygen and uses energy from reaction between them to produce electrical energy

C6.2 Organic Chemistry Flashcards

(40 cards)