DP Chemistry (last assessment 2024)

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Question 19M.3.hl.TZ2.16

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Date May 2019 Marks available [Maximum mark: 9] Reference code 19M.3.hl.TZ2.16
Level hl Paper 3 Time zone TZ2
Command term Calculate, Determine, Outline, State Question number 16 Adapted from N/A
16.
[Maximum mark: 9]
19M.3.hl.TZ2.16

This question is about nuclear reactions.

Fission of a nucleus can be initiated by bombarding it with a neutron.

(a(i))

Determine the other product of the fission reaction of plutonium-239.

94 239 Pu  +  0 1 n → 54 134 Xe  +  . . . . . . . . . . . . . . . . .  +  3 0 1 n

[1]

Markscheme

40 103 Zr   [✔]

Examiners report

This part was well answered.

(a(ii))

Outline the concept of critical mass with respect to fission reactions.

[1]

Markscheme

minimum mass to «self-»sustain chain reaction
OR
if mass of fissile material is too small, too many neutrons produced pass out of the nuclear fuel
OR
at least one neutron produced causes further reaction  [✔]

Examiners report

This part was also fairly well answered although some candidates missed the concept of minimum mass to sustain a chain reaction.

(a(iii))

Outline one advantage of allowing all countries access to the technology to generate electricity by nuclear fission.

[1]

Markscheme

Any one of:
reduction in emission of greenhouse gases «from burning fossil fuels»  [✔]

economic independence/self-sufficiency «from crude oil/producing states» [✔]

uranium is more abundant on Earth «in terms of total energy that can be produced from this fuel» than fossil fuels [✔]

 

Note: Accept specific greenhouse gases (such as carbon dioxide/CO2) but not pollutants or other general statements.

Examiners report

This part saw some reasonable answers, but some other candidates wrote very vague or general answers.

(b)

State one advantage of using fusion reactions rather than fission to generate electrical power.

[1]

Markscheme

Any one of:
fuel is inexpensive/readily available [✔]
no/less radioactive waste is formed [✔]
lower risk of accidents/large-scale disasters [✔]
impossible/harder to use for making materials for nuclear weapons [✔]
larger amounts of energy released per unit mass [✔]
does not require a critical mass [✔]
can be used continuously [✔]

 

Note: Accept “higher specific energy for fusion”.

Do not accept “no/less waste produced for fusion”.

Accept specific example for a disaster.

Examiners report

This was a well-answered question with most candidates referring to fusion having less or no radioactive waste.

(c)

Outline how the energy of a fission reaction can be calculated.

[1]

Markscheme

mass difference between reactants and products AND E = mc2  [✔]

Examiners report

Most of the candidates were able to state correctly the mass difference between reactants and products and E = mc2.

(d)

Calculate the half-life of an isotope whose mass falls from 5.0 × 10−5 g to 4.0 × 10−5 g in 31.4 s, using section 1 of the data booklet.

[2]

Markscheme

«N = N0e–λt»

λ«=  − ln ⁡ ( N N 0 ) t = − ln ⁡ ( 4.0 × 10 − 5 5.0 × 10 − 5 ) 31.4  s »

= 7.106 × 10–3 s–1  [✔]

«  t 1 2 = ln ⁡ 2 λ =» 98/97.5 «s» [✔]

 

Note: Award [2] for correct final answer.

Examiners report

Many candidates were able to calculate the half-life of an isotope correctly.

(d)

Calculate the half-life of an isotope whose mass falls from 5.0 × 10−5 g to 4.0 × 10−5 g in 31.4 s, using section 1 of the data booklet.

[2]

Markscheme

«N = N0e–λt»

λ«=  − ln ⁡ ( N N 0 ) t = − ln ⁡ ( 4.0 × 10 − 5 5.0 × 10 − 5 ) 31.4  s »

= 7.106 × 10–3 s–1  [✔]

«  t 1 2 = ln ⁡ 2 λ =» 98/97.5 «s» [✔]

 

Note: Award [2] for correct final answer.

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