A-Level Chemistry (OCR) > 4.3 Alcohols and Haloalkanes > Flashcards

4.3 Alcohols and Haloalkanes Flashcards

Predict reactions of alcohols and haloalkanes using substitution, elimination, and oxidation mechanisms. (79 cards)

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1
Q

What type of bond is present between carbon and halogen atoms in halogenoalkanes?

A

Polar covalent bond

The electronegative halogen pulls electron density away from carbon.

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2
Q

What type of reaction occurs when a halogenoalkane reacts with a nucleophile?

A

Nucleophilic substitution

The nucleophile replaces the halogen atom.

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3
Q

Fill in the blank:

A species that donates a lone pair of electrons to form a bond is called a _______.

A

nucleophile

Nucleophiles are electron-pair donors.

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4
Q

True or False:

Aqueous Hydroxide ions can act as nucleophiles in substitution reactions.

A

True

OH- attacks the electron-deficient carbon atom.

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5
Q

What product forms when a halogenoalkane reacts with hydroxide ions?

A

Alcohol

The OH- replaces the halogen atom.

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6
Q

True or False:

Cyanide ions reacting with halogenoalkanes increase the carbon chain length.

A

True

CN- introduces an additional carbon atom to the molecule.

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7
Q

Fill in the blank:

Reaction of a halogenoalkane with ammonia forms a _______.

A

amine

NH3 replaces the halogen to form an amine group.

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8
Q

Why is the carbon atom in a halogenoalkane susceptible to nucleophilic attack?

A

Partial positive charge

The polar C–X bond leaves carbon slightly electron deficient.

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9
Q

True or False:

The strength of the carbon–halogen bond affects the rate of nucleophilic substitution.

A

True

Weaker bonds break more easily and react faster.

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10
Q

Fill in the blank:

As the carbon–halogen bond enthalpy decreases, the rate of reaction generally _______.

A

increases

Iodoalkanes react faster than chloroalkanes. bromoalkanes are in the middle.

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11
Q

Which halogenoalkane typically reacts fastest in nucleophilic substitution reactions?

A

Iodoalkane

The C–I bond is weakest among common halogenoalkanes. This is because the bond length is greater thus the nuclear attraction to the outer electrons is weaker.

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12
Q

Why do iodoalkanes react faster than chloroalkanes in substitution reactions?

A

Weaker carbon–halogen bond

Lower bond enthalpy makes bond breaking easier.

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13
Q

What type of reaction forms an alkene from a halogenoalkane by removing a hydrogen halide?

A

Elimination

A hydrogen atom and a halogen atom are removed from adjacent carbons.

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14
Q

What type of organic product is formed during elimination of a halogenoalkane?

A

Alkene

The reaction creates a carbon–carbon double bond.

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15
Q

Fill in the blank:

During elimination, a halogenoalkane loses hydrogen and a _______ atom.

A

halogen

The removed atoms combine to form HX.

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16
Q

True or False:

Elimination and substitution reactions can occur simultaneously in halogenoalkane reactions.

A

True

The reaction conditions determine which pathway dominates.

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17
Q

What reagent is commonly used to cause elimination in halogenoalkanes?

A

Ethanolic Potassium hydroxide

Usually used in ethanolic solution to favour elimination. Ethanolic means dissolved in alcohol

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18
Q

True or False:

Hydroxide ions can act as both nucleophiles and bases.

A

True

They can attack carbon (substitution) or remove a proton (elimination).

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19
Q

Fill in the blank:

In elimination reactions, the ethanolic hydroxide ion acts as a _______ by removing a proton.

A

base

It removes H+ from a neighbouring carbon atom.

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20
Q

What role does aqueous hydroxide play in nucleophilic substitution reactions?

A

Nucleophile

It donates a lone pair to form a new bond with carbon.

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21
Q

True or False:

In elimination reactions, the hydroxide ion removes a hydrogen atom as H+.

A

True

This leads to formation of a double bond between carbons.

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22
Q

Fill in the blank:

The elimination of HBr from 2-bromopropane forms the alkene _______.

A

propene

A double bond forms between two carbon atoms.

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23
Q

Why can potassium hydroxide cause both substitution and elimination reactions?

A

Dual role

OH- can act either as a nucleophile or a base depending on conditions.

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24
Q

What structural change occurs in the organic molecule during elimination?

A

Double bond formation

Removal of HX allows formation of a C=C bond.

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25
What **molecule** in the **upper atmosphere** absorbs harmful ultraviolet radiation?
Ozone ## Footnote O3 absorbs UV radiation and protects living organisms from damage.
26
In which **layer of the atmosphere** is the **ozone layer** found?
Stratosphere ## Footnote The ozone layer is located above the troposphere.
27
# Fill in the blank: **Ozone molecules** contain _\_\_\_\_\_\_ oxygen atoms.
three ## Footnote The chemical formula of ozone is O3.
28
# True or False: **Ozone** protects life on Earth by absorbing **ultraviolet radiation**.
True ## Footnote This prevents harmful UV rays from reaching the Earth’s surface.
29
What **compounds** were once widely used as **refrigerants and solvents** but damage the ozone layer?
Chlorofluorocarbons ## Footnote These compounds are commonly called CFCs.
30
# True or False: **Ultraviolet radiation** can break the **carbon–chlorine bonds in CFCs**.
True ## Footnote This process forms chlorine radicals in the atmosphere.
31
# Fill in the blank: When **CFC molecules break down**, they release chlorine _\_\_\_\_\_\_.
radicals ## Footnote These radicals are highly reactive species with unpaired electrons.
32
What **role** do **chlorine radicals** play in ozone depletion?
Catalysts ## Footnote They speed up ozone decomposition without being consumed.
33
# True or False: **Chlorine radicals** are regenerated during **ozone destruction reactions**.
True ## Footnote This allows one radical to destroy many ozone molecules.
34
# Fill in the blank: In the reaction Cl* + O3 → ClO* + O2, ozone is converted into _\_\_\_\_\_\_.
oxygen ## Footnote Ozone decomposes into molecular oxygen.
35
Why can a single **chlorine radical** destroy many **ozone molecules**?
Catalyst regeneration ## Footnote The chlorine radical is reformed at the end of the reaction cycle. ClO* + O3 → 2O2 + Cl*
36
Why were **CFCs** eventually **banned in many countries**?
Scientific evidence ## Footnote Research showed they were responsible for depletion of the ozone layer.
37
What **industrial process** produces **alcohols from alkenes**?
Hydration ## Footnote Steam adds across the C=C bond in the presence of an acid catalyst.
38
What type of **reaction** converts an **alkene into an alcohol using steam**?
Electrophilic addition ## Footnote The alkene double bond reacts with steam to form an alcohol.
39
# Fill in the blank: In **industrial hydration**, alkenes react with _\_\_\_\_\_\_ to produce alcohols.
steam ## Footnote This reaction uses an acid catalyst such as phosphoric acid.
40
# True or False: **Ethanol** can be produced biologically from **glucose by fermentation**.
True ## Footnote Yeast enzymes convert glucose into ethanol and carbon dioxide.
41
What **microorganism** is commonly used to **ferment glucose to ethanol**?
Yeast ## Footnote Yeast contains enzymes that catalyse the fermentation reaction.
42
# Fill in the blank: The **fermentation of glucose** produces ethanol and _\_\_\_\_\_\_.
carbon dioxide ## Footnote C6H12O6 → 2C2H5OH + 2CO2.
43
# True or False: **Fermentation** occurs efficiently at **temperatures around 30–40 °C**.
True ## Footnote Higher temperatures can kill the yeast enzymes.
44
What **process** is used to separate **ethanol from the fermentation mixture**?
Fractional distillation ## Footnote Ethanol is separated based on its boiling point.
45
# Fill in the blank: A **fuel produced from biological sources** such as plants is called a _\_\_\_\_\_\_ fuel.
biofuel ## Footnote Biofuels are derived from renewable biological materials.
46
Why is **ethanol** sometimes described as a **carbon-neutral fuel**?
Carbon cycle balance ## Footnote CO2 released during combustion equals CO2 absorbed during plant growth.
47
# True or False: **Ethanol produced by fermentation** is perfectly **carbon neutral in practice**.
False ## Footnote Energy used in farming, processing and transport releases additional CO2.
48
Why must **fermentation** occur in the **absence of oxygen**?
Prevent oxidation ## Footnote Oxygen would allow yeast to respire aerobically instead of producing ethanol.
49
How are **alcohols** classified according to the **carbon atom bonded to the –OH group**?
Primary secondary tertiary ## Footnote Classification depends on how many carbon atoms are attached to the carbon bearing the –OH group.
50
What type of **alcohol** has the **–OH group attached to a carbon bonded to only one other carbon**?
Primary alcohol ## Footnote Example: ethanol.
51
# Fill in the blank: A **secondary alcohol** has the –OH group attached to a carbon bonded to _\_\_\_\_\_\_ other carbons.
two ## Footnote The central carbon is connected to two alkyl groups.
52
# True or False: **Tertiary alcohols** are easily **oxidised under normal laboratory conditions**.
False ## Footnote They resist oxidation because the –OH carbon lacks a hydrogen atom.
53
What **oxidising agent** is commonly used to oxidise alcohols in the laboratory?
Acidified potassium dichromate ## Footnote K2Cr2O7 in acidic conditions is a common oxidising agent.
54
# True or False: **Primary alcohols** can be oxidised first to **aldehydes and then to carboxylic acids**.
True ## Footnote Further oxidation occurs if strong oxidising conditions are used.
55
# Fill in the blank: Oxidation of a **secondary alcohol** produces a _\_\_\_\_\_\_.
ketone ## Footnote The carbon–oxygen double bond forms at the alcohol carbon.
56
What determines whether a **primary alcohol** forms an **aldehyde or a carboxylic acid** during oxidation?
Reaction conditions ## Footnote Distillation forms aldehydes; reflux allows further oxidation to acids.
57
# True or False: **Distillation** is used during oxidation to collect **aldehydes before they oxidise further**.
True ## Footnote Aldehydes have lower boiling points and can be removed from the reaction mixture.
58
# Fill in the blank: The reagent that produces a **silver mirror with aldehydes** is _\_\_\_\_\_\_ reagent.
Tollens ## Footnote Aldehydes reduce [Ag(NH3)2]+ to metallic silver.
59
What **observation** occurs when **Fehling’s solution reacts with an aldehyde**?
Brick red precipitate ## Footnote The aldehyde reduces Cu2+ to Cu2O.
60
Why do **ketones** not react with **Tollens’ reagent**?
Not easily oxidised ## Footnote Ketones lack the hydrogen needed for oxidation under these conditions.
61
What type of **reaction** forms an **alkene from an alcohol** by removing water?
Elimination ## Footnote The alcohol loses H2O to form a C=C double bond.
62
What **molecule** is removed from an **alcohol during elimination** to form an alkene?
Water ## Footnote The reaction is often called dehydration of an alcohol.
63
# Fill in the blank: **Acid-catalysed elimination of alcohols** produces _\_\_\_\_\_\_.
alkenes ## Footnote A double bond forms between adjacent carbon atoms.
64
# True or False: **Elimination of alcohols** requires an **acid catalyst**.
True ## Footnote Concentrated acids such as H2SO4 or H3PO4 are typically used.
65
What **role** does the **acid** play in the elimination of water from alcohols?
Catalyst ## Footnote It helps protonate the –OH group to make water a better leaving group.
66
# True or False: The **–OH group** in alcohols is converted into **water before leaving the molecule**.
True ## Footnote Protonation forms H2O, which can leave more easily than OH-.
67
# Fill in the blank: In the **elimination mechanism**, the alcohol is first _\_\_\_\_\_\_ to form a better leaving group.
protonated ## Footnote The –OH group gains a proton to become H2O.
68
What **structural change** occurs in the molecule during **elimination of an alcohol**?
Double bond formation ## Footnote A C=C bond forms after removal of H2O.
69
# True or False: **Alkenes produced from alcohols** can be used to make **addition polymers**.
True ## Footnote These alkenes can act as monomers in polymerisation reactions.
70
# Fill in the blank: The **elimination of water from alcohols** is also called _\_\_\_\_\_\_.
dehydration ## Footnote This term refers to removal of H2O from the molecule.
71
What **laboratory technique** is used to purify **cyclohexene produced from cyclohexanol**?
Distillation ## Footnote The alkene is separated based on its boiling point.
72
Why is producing **alkenes from alcohols** environmentally beneficial compared with crude oil sources?
Renewable feedstocks ## Footnote Alcohols can be derived from biomass rather than fossil fuels.
73
What equation shows **CO₂ absorption during photosynthesis** (production of ethanol source)?
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
74
What equation shows **fermentation of glucose to produce ethanol**?
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
75
What **equation shows combustion of ethanol**?
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
76
What is the **general oxidation equation** for a **primary alcohol to an aldehyde**?
RCH₂OH + [O] → RCHO + H₂O
77
What is the **general oxidation equation** for an **aldehyde to a carboxylic acid**?
RCHO + [O] → RCOOH
78
What is the **oxidation equation for a secondary alcohol**?
R₁CHOHR₂ + [O] → R₁COR₂ + H₂O
79
What is the **overall oxidation equation** for a **primary alcohol to a carboxylic acid**?
RCH₂OH + 2[O] → RCOOH + H₂O
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