f322 Flashcards

1
Q

shape and bond angle of alkanes

A

4 bond pairs on the central atom

Equal repulsion between bond pairs

Tetrahedral

109.5’

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2
Q

shape and bond angle of alkenes

A

4 electron pairs on the central atom

1 double bond acts as one bond pair

3 bond pairs on the central atom

Equal repulsion between bond pairs

Trigonal planar

120’

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3
Q

state and explain the effect of an increasing chain length on the boiling points of the alkanes

A

As the chain length of alkanes increases the points of contact between molecules increases.
There are more intermolecular London forces between the molecules.
More energy is needed to break the stronger London forces between the molecules.
Boiling point increases.

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4
Q

state and explain the effect of an increasing branching on the boiling points of the alkanes

A

As the branching of alkanes increases the points of contact between molecules decreases.
There are less intermolecular London forces between the molecules.
Less energy is needed to break the weaker London forces between the molecules.
Boiling point decreases.

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5
Q

what are the limitations of radical substitution

A

Uncontrollable termination steps leading to a mixture of products
Further propagation steps of the mono-substituted product to form poly-substituted halogenoalkanes.

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6
Q

how does fractional distillation separate crude oil

A

Separation of a liquid mixture into fractions with different boiling points.
Longer chain higher boiling point (more London forces between the molecules) so separate at the bottom (hotter).
Shorter chain lower boiling point so separate at the top.

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7
Q

why are longer chain alkanes processed further

A

longer chain alkanes are more efficient fuels which are easier to burn.

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8
Q

how does incomplete combustion occur

A

Insufficient oxygen supply.

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9
Q

advantage/ disadvantage of fossil fuels.

A

Good source of energy

Non-renewable ( and crude oil takes millions of years to form)

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10
Q

why might biofuels replace crude oil

A

Renewable (biodiesel from rape seed, ethanol from sugar cane fermentation)

Less CO2 emissions during combustion

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11
Q

describe how the rates of hydrolysis of halogenoalkanes (chloro, bromo, iodo) could be measured

A

Add AgNO3(aq)

Add ethanol and heat

Time how long it takes for a precipitate to form (chloro white precipitate, bromo cream precipitate and Iodo yellow precipitate)

RX + H2O → ROH + HX

X(aq) + Ag+(aq) → AgX(s)

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12
Q

explain the rate of hydrolysis of the halogenoalkanes

A

C-I bond weakest and C-I bond needs least energy to break

Iodoalkane fastest rate of reaction

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13
Q

why might calculated enthalpy values differ from theoretical (standard) values using

A

a) mc∆T (Method 1)
1. Heat loss (when exothermic) or heat gain (when endothermic)
2. Not done under standard conditions

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14
Q

explain why an alkene displays stereoisomerism (and which type)

A

E/Z:
C=C can’t rotate
2 different groups attached to each carbon

Cis-Trans:
C=C can’t rotate
2 different groups attached to each C
2 substituent groups the same

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15
Q

describe the formation of a pi, π bond

A

Sideways double overlap of p-orbitals from two adjacent C atoms

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16
Q

advantages and disadvantages associated with addition polymers

A

Advantages:
Many uses
Durable

Disadvantages:
Release toxic gases when burned
Non biodegradable

17
Q

describe the ways in which chemists are trying to minimise the impact of the disadvantages associated with addition polymer usage

A

Separation (using identification codes) and recycling
Feedstock in other chemical reactions
Combustion for energy (via controlled combustion using toxic gas removers)
Developing biodegradable polymers from renewable raw materials e.g. maize and starch

18
Q

Describe the solubility of alcohols in water

A

Polar (hydrophilic) OH group forms hydrogen bonds with polar water molecules
Solubility decreases as chain length increases as a greater proportion of the alcohol molecule is non-polar (hydrophobic)

19
Q

what is/how to identify Mass Spectroscopy

A

Molecular ion peak furthest to the right with the highest m/z value is the molecular mass

20
Q

describe ways scientists are improving sustainability

A

Renewable energy sources (e.g. wind and solar)
Improved atom economy in chemical reactions (alternative reactions with catalysts and a use for by-products)
Reducing/ eliminating hazardous chemical (e.g. recycle, re-use, enzymes etc.)