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CHEMISTRY AS > KERBOODLE PRACTICE QUESTIONS: OZ > Flashcards

KERBOODLE PRACTICE QUESTIONS: OZ Flashcards

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1
Q

The following substances all have similar Mr values.
Which has the highest boiling point?

A) CH3CH2CH2CH3

B) CH3CH2Cl

C) CH3CH2CH2OH

D) CH3COCH3

A

C) CH3CH2CH2OH

Molecules can form hydrogen bonds

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2
Q

Which of the following molecules would have the greatest overall dipole?

A) CCl4

B) BF3

C) NH3

D) C2H6

A

C) NH3
NH3 is pyramidal so N-H bond polarities do not cancel. In all the others they do.

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3
Q

Nitrogen and hydrogen are mixed. Which of the following conditions would result in the equilibrium being set up fastest?

N2 + 3H2 –> 2NH3 exothermic

A) pressure = high
temperature = high

B) pressure = high
temperature = low

C) pressure = low
temperature = high

D) pressure = low
temperature = low

A

A) pressure = high
temperature = high

Note it is rate not equilibrium yield that is being asked for here

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4
Q

Which of the following are correct statements about the role of CFCs in ozone depletion?

A) Troposphere: no ozone to deplete
Stratosphere: form Cl radicals that deplete ozone

B) Troposphere: do not form Cl radicals
Stratosphere: form Cl radicals that deplete ozone

C) Troposphere: no ozone to deplete
Stratosphere: react with ozone to deplete it

D) Troposphere: do not form Cl radicals
Stratosphere: react with ozone to deplete it

A

B) Troposphere: do not form Cl radicals
Stratosphere: form Cl radicals that deplete ozone

There is some ozone in the troposphere. CFCs break down before they deplete ozone

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5
Q

Which of the following statements is correct about UV radiation in the stratosphere?

A) It is reflected from the Earth

B) It comes from the Sun and is all absorbed

C) It breaks down molecules

D) It causes photochemical smog

A

C) It breaks down molecules

A - vague but certainly untrue. B – not all absorbed. C – true in the troposphere

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6
Q

The names of some bromoalkanes and their boiling points are shown below
Name = 1-bromobutane
Boiling point/K = 375
Name = 2-bromobutane
Boiling point/K = 364
Name = 2-bromo-2-methylpropane
Boiling point/K = 346

Which of the following is a correct statement?

A) The dipole of the C-Br bond is largest in 1-bromobutane.

B) The instantaneous dipole-induced dipole gets weaker as the molecules become more compact

C) The molecules contain different numbers of electrons

D) 1-bromobutane is the most volatile

A

B) The instantaneous dipole-induced dipole gets weaker as the molecules become more compact

A –same in each. C – all the same. D – least volatile

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7
Q

Hydrogen bonds can form between which of the following pairs of atoms in molecules?

A) Any hydrogen atom
An oxygen atom in a molecule

B) A hydrogen atom attached to a nitrogen atom
A nitrogen atom in a molecule

C) Any hydrogen atom
A fluorine atom in a molecule

D) A hydrogen atom attached to a chlorine atom
A carbon atom attached to a chlorine atom

A

B) A hydrogen atom attached to a nitrogen atom
A nitrogen atom in a molecule

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8
Q

Which of the following is a characteristic of a catalyst?

  • *Statement 1:** It provides a route of lower activation enthalpy
  • *Statement 2:** It is unchanged at the end of the reaction
  • *Statement 3:** It does not take part in the reaction

A) 1,2 and 3 are correct

B) 1 and 2 are correct

C) 2 and 3 are correct

D) Only 1 is correct

A

B) 1 and 2 are correct

3 is not true, a catalyst may take part in a reaction, provided it is unchanged at the end.

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9
Q

Which of the following are characteristics of a nucleophile?

  • *Statement 1:** It must have a negative (or partial negative) charge.
  • *Statement 2:** It attacks positively charged atoms
  • *Statement 3:** It has a lone pair of electrons

A) 1,2 and 3 are correct

B) 1 and 2 are correct

C) 2 and 3 are correct

D) Only 1 is correct

A

C) 2 and 3 are correct

1 is not true as molecules can be nucleophiles

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10
Q

Which of the following are termination steps in the radical chlorination of methane?
CH4 + Cl2 –> CH3Cl + HCl
Statement 1: 2CH3 –> C2H6
Statement 2: 2Cl –> Cl2
Statement 3: CH3 + Cl –> CH3Cl

A) 1,2 and 3 are correct

B) 1 and 2 are correct

C) 2 and 3 are correct

D) Only 1 is correct

A

A) 1,2 and 3 are correct

Mechanism is: Cl2 → 2Cl.
Cl + CH4 → CH3 + HCl.
CH3 + Cl2 → CH3Cl + Cl.

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11
Q

The hydroxyl radical OH has been described as ‘the detergent of the atmosphere’ as it is able to oxidise (and thus remove) most substances in the troposphere.

It is made by the reaction of oxygen atoms with water molecules:
O + H2O –> 2OH

Draw a ‘dot-and-cross’ diagram for a hydroxyl radical and explain why OH is called a radical.

A

(diagram)
atom/molecule/ion/species with an unpaired electron

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12
Q

Oxygen atoms are formed in the troposphere by the photolysis of ozone

Write an equation for the photolysis of ozone

A

O3 → O2 + O

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13
Q

Oxygen atoms are formed in the troposphere by the photolysis of ozone

3% of oxygen atoms are removed from the atmosphere by the reaction O + H2O –> 2OH. Suggest another equation related to the photolysis of ozone by which oxygen atoms are removed from the atmosphere.

A

O + O2 → O3

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14
Q

In the stratosphere, oxygen molecules are broken down by photolysis.

Given that the bond enthalpy of O=O is 498kJ mol-1, calculate the minimum frequency of electromagnetic radiation needed to break this bond.

Then calculate the corresponding wavelength to this frequency

Then suggest why this reaction only takes place in the stratosphere, whereas the photolysis of ozone takes place in the troposphere

A

Energy per atom = 498 000/ 6.02 × 1023
(= 8.27 × 10−19)
Frequency = E/h
= (= 8.27 × 10−19) / 6.63 × 10−34
= 1.25 × 1015 Hz
must have units for final mark (could be given as s-1)

λ = c/v
= 3.00 × 108 / (1.25 × 1015)
= 2.40 × 10−7 m (or 240 nm)

UV of this frequency is only available in the stratosphere
ozone photolysis happens at lower energy/ lower frequency/ higher wavelength which is present in the troposphere

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15
Q

Carbon monoxide is one of the major substances removed from the troposphere by hydroxyl radicals

CO + OH –> CO2 + H
Classify the reaction as initiation, propagation or termination, giving a reason.

A

propagation
one radical on each side of the equation

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16
Q

Some students carry out experiments with 1-chlorobutane, 1-bromobutane, and 1-iodobutane

The students wish to discover the relative rates of hydrolysis of the three haloalkanes, using silver nitrate solution and ethanol

Describe how they would carry out the experiment. Give equations for the reactions that occur and say what is seen.

A

mix haloalkane, AgNO3, ethanol
time for precipitate to form
precipitates form in order of iodo (fastest), bromo, chloro
C4H9X + H2O –> C4H9OH + HX (or H+ + X-)
Ag+ + X- –> AgX

suitable apparatus (e.g. test tube)
equal vols of each
add AgNO3 last and starting time
chloro = white precipitate
bromo = cream precipitate
iodo = yellow precipitate

17
Q

Some students carry out experiments with 1-chlorobutane, 1-bromobutane and 1-iodobutane

Before the experiment, one student predicts that the haloalkane with the greatest permanent dipole will react fastest

Explain what is meant by permanent dipole and explain which of the haloalkanes used by the students has the greatest permanent dipole

A

molecule (or bond) that has one end slightly positive (or δ+), the other slightly negative (or δ–)
1-chlorobutane has greatest dipole
chlorine is the most electronegative of the three halogens

18
Q

Some students carry out experiments with 1-chlorobutane, 1-bromobutane and 1-iodobutane

The student uses the mechanism of the reaction to justify the prediction.

Draw out the mechanism of the reaction for the hydrolysis of 1-chlorobutane with water, showing curly arrows and partial charges.

Then indicate one heterolytic bond-breaking that occurs in the mechanism

A

[mechanism]
breaking of C–Cl

19
Q

Some students carry out experiments with 1-chlorobutane, 1-bromobutane and 1-iodobutane

The students wish to discover the relative rates of hydrolysis of the three haloalkanes, using silver nitrate solution.

Before the experiment, one student predicts that the haloalkane with the greatest permanent dipole would react fastest.

Explain why the haloalkane with the greatest dipole might have reacted fastest.

A

greater δ+ on C attracts water more

20
Q

Some students carry out experiments with 1-chlorobutane, 1-bromobutane and 1-iodobutane

The students wish to discover the relative rates of hydrolysis of the three haloalkanes, using silver nitrate solution.

Before the experiment, one student predicts that the haloalkane with the greatest permanent dipole would react fastest.

State and explain the more important factor in determining the rate of hydrolysis.

A

bond strength
C–I weakest
C–Cl strongest

21
Q

Students carry out a reaction in which they heat 1-bromobutane with concentrated ammonia in a sealed tube. Write an equation for the reaction that will occur and name the functional group in the product.

A

C4H9Br + NH3 → C4H9NH2 + HBr
Amine

22
Q

When aircraft started flying in or near to the stratosphere, there were concerns that nitrogen oxides in their exhauts would catalyse the breakdown of ozone in the equation:
O + O3 –> 2O2
The first reaction by which NO breaks down ozone is:
Equation 2: NO + O3 –> NO2 + O2
NO is a catalyst in the breakdown of ozone by the first reaction. Write the equation for the reaction that follows equation 2.

A

NO2 + O –> NO + O2

23
Q

When aircraft started flying in or near to the stratosphere, there were concerns that nitrogen oxides in their exhauts would catalyse the breakdown of ozone in the equation:
O + O3 –> 2O2
The first reaction by which NO breaks down ozone is:
Equation 2: NO + O3 –> NO2 + O2

What type of catalysis is involved here?

A

homogeneous

24
Q

In order to be a catalyst, the activation enthalpy of the catalysed reaction must be smaller than that for the uncatalysed reaction.

Explain the meaning of the term activation enthalpy.

A

the energy with which a pair of molecules must collide in order to react

25
Q

Label the Boltzmaan distribution below to show how adding a catalyst makes a reaction go faster.

A

Shaded part labelled as extra molecules with energy greater than Ea

26
Q

Complete the enthalpy profile below to show that a catalysed reaction has lower activation enthalpy than the uncatalysed reaction

A
27
Q

Why is there concern about the destruction of the ozone layer?

A

ozone absorbs high-energy UV
that causes skin cancer, mutations, and so on

28
Q

When aircraft started flying in or near to the stratosphere, there were concerns that nitrogen oxides in their exhauts would catalyse the breakdown of ozone in the equation:
O + O3 –> 2O2
The first reaction by which NO breaks down ozone is:
Equation 2: NO + O3 –> NO2 + O2

It was later discovered that the effect of NO from aircraft on the ozone layer was very small compared with the effect of another radical from human-derived sources.

Give the name of this radical and its source in the stratosphere.

A

Cl radicals
breakdown of CFCs

CHEMISTRY AS (24 decks)

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