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Chemistry > Module 4.2 - Alcohols, Haloalkanes and Analysis > Flashcards

Module 4.2 - Alcohols, Haloalkanes and Analysis Flashcards

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1
Q

What is the general formula of an alcohol?

A

CnH2n+1OH

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2
Q

What 3 groups can alcohols be classified into?

A
  • primary alcohol
  • secondary alcohol
  • tertiary alcohol
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3
Q

What is a primary alcohol?

A
  • has the functional group attached to a carbon atom with no more than one alkyl group
  • OH at t6he end of a chain
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4
Q

What is a secondary alcohol?

A

-has the functional group attached to a carbon atom with two alkyl chains (+one H)

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5
Q

What is a tertiary alcohol?

A

-has the functional group attached to a carbon atom with 3 alkyl groups

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6
Q

Describe the trend in boiling points of alcohols of increasing chain length.

A
  • increases as chain length increases
  • as molecules get longer more areas of surface contact
  • stronger/more London forces
  • more energy needed to overcome these attractive forces
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7
Q

Compare the boiling points of alcohols with their corresponding alkanes.

A
  • higher than alkanes
  • H bonds between alcohol molecules
  • H bonds stronger than London forces
  • more energy needed to overcome H bonds than London forces
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8
Q

What does it mean if a substance is volatile?

A
  • evaporates easily at room temp/pressure

- volatility increases as boiling point decreases

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9
Q

Compare the volatility of alcohols and their corresponding alkanes.

A

alcohols have H bonds so are less volatile than corresponding alkane

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10
Q

Describe the solubility of alcohols and the trends in solubility as chain length increases.

A
  • water molecules are polar + so is the alcohol functional group
  • methanol/ethanol/propanol are soluble in water as molecules form H bonds w molecules (sometimes described as miscibility)
  • as alkyl chain length increases solubility of alcohol decreases because aliphatic chain can’t form H bonds + this become the larger part of the molecule
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11
Q

When would alcohols be combusted?

A
  • used as fuels

- combustion transfers stored chemical energy to a usable form e.g. thermal energy

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12
Q

What are the products of the complete combustion of an alcohol? What is the equation for the complete combustion of ethanol?

A
  • carbon dioxide and water

- C2H5OH(l) + 3O2(g) –> 2CO2(g) + 3H2O(l)

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13
Q

What is formed under gentle heating (distillation) of a primary alcohol and what colour change of the acidified potassium dichromate occurs?

A
  • aldehyde

- orange to green

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14
Q

What is formed under the stronger heating (reflux) of a primary alcohol (in excess acidified potassium dichromate) and what colour change of the acidified potassium dichromate occurs?

A
  • carboxylic acid

- orange to green

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15
Q

What is formed when a secondary alcohol is heated under reflux and what colour change of the potassium dichromate occurs?

A
  • ketone

- orange to green

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16
Q

What is formed when a tertiary alcohol is heated under reflux and what colour change of the potassium dichromate occurs?

A
  • no reaction

- remains orange

17
Q

What are oxidising agents simplified to in equations?

A

[O]

18
Q

What is the equation for the distillation of propan-1-ol?

A

C3H7OH + [O] –(K2Cr2O7/H2SO4)–> C2H5CHO + H2O

propan-1-ol + [O] –> propanal + water

19
Q

What is the equation for the reflux of proan-1-ol?

A

C3H7OH + 2[O] –(K2Cr2O7/H2SO4)–> C2H5COOH + H2O

propan-1-ol + 2[O] –> propanoic acid + water

20
Q

What is the equation for the reflux of butan-2-ol?

A

CH3CHOHCH2CH3 + [O] –(K2Cr2O7/H2SO4)–> CH3CoCH2CH3 + H2O

butan-2-ol + [O] –> butanone + water

21
Q

Describe how an alcohol would be dehydrated.

A
  • water is lost from the organic compound (eliminated)
  • heated with strong acid (e.g. conc H2SO4) water is eliminated making an alkene
  • -OH group from one C atom + H atom on adjacent C atom are lost to form a water molecule
  • pi bonds between the 2 adjacent C atoms
22
Q

What is the general equation for a halide substitution to an alcohol?

A

HX + ROH –> RX + H2O

23
Q

Describe halide substitution to alcohols?

A
  • halide takes place of -OH forming a haloalkane
  • reagent is a hydrogen halide
  • conc acid catalyst + warmed to increase rate of reaction
  • when iodide uses H3PO4 used as H2SO4 oxidises iodide ions to iodine so yield of desired iodialkane is v low
24
Q

What causes haloalkanes to react?

A
  • polar as large difference in electronegativity between C-X
  • electrons in C-X bond spend more time at X so delta charges form
  • carbon atom attacked by atoms/molecules/ions with partial/full -ve charge. These species called nucleophiles
25
Q

Explain the two main factors affecting the reactivity of haloalkanes.

A
  • strength of C-X bond: halogens get larger down the group so bonding electrons further from nucleus = more shielding = lower bond enthalpy so C-X bonds are easier to break. Higher bond enthalpies = less likely the halogen will react in nucleophilic substitution
  • polarity of C-X bond: F = most electronegative halogen (decreases down the group) so polarity of C-X bond decreases down the group + molecules w highest polarity that are more likely to react
26
Q

What is nucleophilic substitution?

A

A reaction where an atom/group of atoms is exchanged for a nucleophile. Nucleophile is attracted to partial positive charge of C atom + donates its lone pair of electrons to form a new covalent bond

27
Q

How does a haloalkane undergo hydrolysis?

A
  • nucleophilic substitution
  • water often used to provide the OH- ions
  • one of the H-O bonds in water undergoes heterolytic fission producing OH- nucleophile
  • species attacks electron deficient carbon atom in haloalkane molecules
  • When OH- bonded, C-X undergoes heterolytic fission to produce a halide ion
28
Q

How could you measure the rate of hydrolysis?

A
  • X- ions produced
  • form a coloured precipitate with silver nitrate
  • see how quick the coloured precipitate forms
29
Q

Which haloalkane would have the fastest rate of hydrolysis and why?

A

C-I as the bond is weaker + easier to break

Chemistry (13 decks)

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