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Chemistry Unit F322 > Basic Concepts and Hydrocarbons > Flashcards

Basic Concepts and Hydrocarbons Flashcards

(48 cards)

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0
Q

Define molecular formula

A

The actual number of atoms of each element in a molecule.

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1
Q

Define empirical formula

A

The simplest whole number ratio of atoms of each element present in a compound.

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2
Q

Define general formula

A

The simplest algebraic formula of a member of a homologous series, ie for an alkane: CnH2n+2

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3
Q

Define structural formula

A

The minimal detail that shows the arrangement of atoms in a molecule

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4
Q

Define displayed formula

A

The relative positioning of atoms and the bonds between them

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5
Q

Define skeletal formula

A

The simplified organic formula, shown by removing hydrogen atoms from alkyl chains, leaving just a carbon skeleton and associated functional groups.

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6
Q

Define homologous series

A

A series of organic compounds having the same functional group but with each successive member differing by CH2

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7
Q

Define functional group

A

A group of atoms responsible for the characteristic reactions of a compound

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8
Q

State the names of the first 10 members of the alkanes homologous series

A

1) Methane- CH4
2) Ethane- C2H6
3) Propane- C3H8
4) Butane - C4H10
5) Pentane- C5H12
6) Hexane- C6H14
7) Heptane- C7H16
8) Octane- C8H18
9) Nonane- C9H20
10) Decane- C10H22

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9
Q

Define structural isomers

A

Compounds with the same molecular formula but different structural formulae.

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10
Q

Define stereoisomers

A

Compounds with the same structural formula but with a different arrangement in space

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11
Q

Define E/Z isomerism

A

An example of stereoisomerism, in terms of restricted rotation about a double bond and the requirement for two different groups to be attached to each carbon atom of the C=C group

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12
Q

Define cis-trans isomerism

A

A special case of E/Z isomerism in which two of the substituent groups are the same

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13
Q

Describe the covalent bond fission: homolytic fission

This could be the definition

A

It is the breaking of a covalent bond, with one of the bonded electrons going to each atom, forming two radicals

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14
Q

Describe the covalent bond fission: heterolytic fission

This could be the definition

A

It is the breaking of a covalent bond with both of the bonded electrons going to one of the atoms, forming a cation (+ ion) and anion (- ion)

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15
Q

Describe a ‘curly arrow’

A

The movement of an electron pair, showing either breaking or formation of a covalent bond

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16
Q

What is the equation for atom economy?

A

(Mr of desired products/sum of Molecular masses of all products) X100%

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17
Q

What is a hydrocarbon

A

A compound of hydrogen and carbon only

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18
Q

Explain the use of crude oil…

A

As a source of hydrocarbons, separated as fractions with different boiling points by fractional distillation, which can be used as fuels or for processing into petrochemicals

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19
Q

Which of the following are saturated hydrocarbons?
Alkenes
Alkanes
Cycloalkanes

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A

Alkanes and cycloalkanes

20
Q

State and explain the tetrahedral shape around each carbon atom in alkanes

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A
  • Each carbon atom in an alkane can bond to 4 hydrogens.
  • > the pairs of electrons in these covalent bonds repel each other and so they arrange themselves around the carbon atom as far apart as possible
  • > due to there being 4 binds with, with no lone pairs, it has a tetrahedral shape, with bond angles of 109 degrees
21
Q

Explain, in terms of van den Waals’ forces, the variations in the boiling points of alkanes with different carbon-chain length and branching.

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A
  • The longer the carbon chain, the higher the boiling point. This is due to the increasing Van der Waals forces between the molecules.
  • The more branched the alkanes the lower the boiling points. Branched alkanes have fewer points of contact and thus reduces the van der Waals’ forces of attraction.
22
Q

Describe the combustion of alkanes, leading to their use as fuels in industry, in the home and I’m transport

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A

-when combustion of hydrocarbon is complete there will always be CO2 and H2O as products.

CH4 + 2O2 -> CO2 + 2H2O
C8 + 12 1/2 O2 -> 8CO2 + 9H2O

23
Q

Explain, using equations, the incomplete combustion of alkanes in a limited supply of oxygen and outline the potential dangers arising from production of CO in the home and from car use.

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A

-Incomplete combustion occurs when not enough oxygen is present.
-equation that occurs when methane is burnt in a limit supply of oxygen: 2CH4(g)+3O2(g) -> 2CO2(g)+4H2O(g)
-equation for incomplete combustion of ethane:
2C2H6(g)+5O2(g) -> 4CO(g)+6H2O(g)

Potential Dangers:
-carbon monoxide can cause oxygen deprivation and you can experience things like fatigue, headaches and nausea.

24
Describe the use of catalytic cracking to obtain more useful alkanes and alkenes.
Cracking is breaking long chain alkanes into smaller hydrocarbons. It involves the breaking of C-C bonds and you end up with a mixture of alkanes and alkanes. Using a catalyst cuts costs, because the reaction can be done at a lower temperature and pressure.
25
Why does the petroleum industry process straight-chain hydrocarbons into branched chain alkanes and cyclic hydrocarbons.
To promote efficient combustion
26
Advantages and disadvantages of fossil fuels.
Advantages: -used as an energy source and as raw materials in the production of plastics and petrochemicals Disadvantages: - burning fossil fuels produces CO2 which is a green house gas and contributes to global warming - fossil fuels are non-renewable and will eventually run out
27
What is the importance of developing renewable plant-based fuels, ie alcohols and biodiesel
- Bio fuels are fuels derived from recently living material such as plants, or from animal waste. - The idea of these types of fuels is that they will be renewable, fast and easy to produce and can be relatively cheap. - We need these types of fuels as our current sources of energy are depleting rapidly. Sources are: - sugar cane - ethanol: made by fermentation of sugar and other carbohydrates, combusts efficiently in a plentiful supply of oxygen, - biodiesel: produced from rapeseed crops, 100% pure
28
How does increased CO2 levels from combustion of fossil fuels lead to global warming and climate change
Burning hydrocarbons increases atmospheric pollutants, such as - carbon monoxide: toxic, formed by incomplete combustion - carbon dioxide: contributes to global warming via greenhouse effect - nitrogen dioxides: acid rain and destruction of forests - sulfur dioxide: acid rain Greenhouse gases prevent heat escaping the atmosphere, leading to global temperature increase.
29
Describe the substituent of alkanes using UV light, by Cl2 and Br2, to form halogenoalkanes.
Alkanes react with UV light or at temperatures of about 300*C Initiation- homolytic fission Cl2 -> Cl + Cl (both are free radicals- no sign for dot thing) Propagation Step 1: CH4 + Cl -> CH3 + HCL Step 2: CH3 + Cl2 -> CH3Cl + Cl Termination 1. Cl + Cl -> Cl2 2. CH3 + CH3 -> C2H6 3. CH3 + Cl -> CH3Cl
30
Define the term radical
Species with an unpaired electron
31
Describe how homolytic fission leads to the mechanism of radical substitution in alkanes in terms of initiation, propagation and termination reactions.
When homolytic fission occurs, each atom is left with unpaired electron, so is now a free radical. As atoms like to have a full outer shell, the radicals then react so that they can, leading to the radical substation mechanism.
32
Explain the limitations of radical substitution in synthesis, arising from further substitution with formation of a mixture of products.
In synthesis, radical substitution is fairly inefficient. | In the termination steps, other organic products can form, so the product needed is not a 100% guarantee.
33
Are alkenes and cycloalkenes... | Unsaturated hydrocarbons or saturated hydrocarbons?
Unsaturated hydrocarbons
34
Describe the overlap of adjacent p-orbitals to form a Pi bond.
A Pi bond is formed by the overlapping of P-orbitals of two carbon atoms. Each carbon contributes one electron to the electron pair in a Pi bond.
35
State and explain the trigonal planar shape around each carbon in the C=C alkenes.
- 3 bonds (1 is a double bond) so 3 regions of electron density around each carbon. - the pairs of electrons repel each other as far away as they can. - due to this, the double bond and the two single pairs produce a trigonal planar shape, with bond angles of 120*
36
Describe addition reactions of alkenes with hydrogen in the presence of a suitable catalyst.
H2C=CH2 + H2 -> C2H6 Nickel (Ni) catalyst and 150*C
37
Describe addition reactions of alkenes with halogens to form dihalogenoalkanes, including the use of bromine to detect the presence of a double C=C bond as a test for unsaturation.
H2C=CH2 + Cl2 -> C2H4Cl2 When bromine is added to a sample containing an alkene, it turns from ORANGE to COLOURLESS.
38
Describe addition reactions of alkenes with hydrogen halides to form halogenoalkanes
Draw curly arrow diagram to explain | e.g. C4H8 + H-Br -> C4H9 + Br- -> C4H8Br
39
Describe addition reactions of alkenes with steam in presence of an acid catalyst to form alcohols.
H2C=CH2 + H2O (g) -> C2H5OH In presence of H3PO4, 60 atm and 300*C
40
Define an electrophile
An electron pair acceptor
41
Describe how heterolytic fission leads to the mechanism of electrophile can addition in alkenes
- Use curly arrows to show movement of an electron pair. - Arrow should show the shared pair of electrons moving to the Br atom. This means that Br is now a negative anion, and H is now a positive cation; hence heterolytic fission C4H8 + H-Br -> C4H9 + Br- -> C4H8Br
42
Describe the addition polymerisation of alkenes
When alkenes are polymerised, they go from there monomer form to their polymer form. The monomer form is unsaturated and has a C=C bond. The polymers is saturated, with only single bonds.
43
Deduce the repeat unit of an addition polymer obtained from a given monomer.
C2H4 (monomer) -> C4H8 (polymer with 2 repeat units) -> (C2H4)n (polymer- general) To be sure, draw structural formula
44
Outline the use of alkenes in the industrial production of organic compounds.
Alkenes may be used in order to form a number of industrial products, such as... 1. 1,2-dichloroethane as a degreaser 2. Ethane -1,2-idol as antifreeze 3. Ethanoic acid as vinegar 4. Poly(tetrafluoroethene) as Teflon 5. The manufacture of margarine by catalytic hydrogenation of unsaturated vegetable oils using hydrogen and a nickel catalyst
45
What are the formation of a range of polymers using unsaturated monomer units based on the ethene molecule, Ie. H2C=CHCl, F2C=CF2
Ethene (H2C=CH2) -> poly(ethene) | Chloroethene (HClC=CHCl) -> poly(chloroethene) PVC
46
Outline the processing of waste polymers.
- separation into types (ie PTFE, etc) and recycling - combustion for energy production - use as a feedstock for cracking in the production of plastics and other chemicals
47
Outline the role of chemists in minimising environmental damage.
-removal of toxic waste products (ie removal of HCL formed during disposal by combustion of halogenated plastics) -PVC recycling plants have been opened in order to separate PVC from other scrap by dissolving it in solvents. -high quality PVC is then recovered by precipitation form of solvent. The solvent can be reused. -development of biodegradable and compostable polymers

Chemistry Unit F322 (2 decks)

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