The following is an extract from the sqa course Support Notes for National 5 Chemistry: Task 2



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The following is an extract from the SQA course Support Notes for National 5 Chemistry:
Task 2

Assessment Standards 2.2 and 2.3 can be achieved using one or two pieces of evidence covering work done on different occasions.


Assessors should record evidence of achievement of Outcomes and Assessment Standards. The table shown is one way of recording the evidence. This table is not mandatory.
This candidate has passed both Assessment Standards 2.2 and 2.3




Isotopes

An isotope is an atom with the same number of protons and electrons, but a differing number of neutrons. Isotopes are all variants of a particular chemical element.


The nuclide notation of an isotope tells you the atomic and the mass number of that particular isotope. The atomic number is the same as the number of electrons and the number of protons. In an atom, each proton and neutron has a mass off 1amu (atomic mass unit), however the relative atomic mass of an electron is almost 0amu. This means that the mass number of an atom is the number of protons plus the number of neutrons.
Americium 241 was discovered in 1944 and is used in a common household object. Americium (Am) is a substance made by scientists and has an atomic number 95. The nuclide notation for americium is:


241

Am

95

The isotope americium 241 is used in some domestic smoke detectors. It has a half life of 432 years which means it will take 432 years for half of the substances to decay. It can be used in smoke detectors because it emits and alpha particle which doesn’t penetrate very far stopping in a few centimetres of air. As the half life is 432 years this isotope will last for a long time and will not need to be replaced.




241

Am




237

Np +

4

He

95

93

2

The alpha particles are constantly released and knock electrons off the atoms in air. This makes these atoms into ions which are attracted to the negatively charged plate and the electrons are attracted to the positively charged plate generating a small current. When smoke enters the chamber the smoke particles attach to the ions and reduce the current flowing. This drop in current triggers the alarm. These are very sensitive detectors.


The amount of Americium 241 used in smoke detectors is very small and the alpha particles will not escape from the chamber. This means they are safe for household use. This isotope has had a very positive effect on society as these smoke detectors are cheap, easy to install and have saved many people’s lives from fire. However as these smoke detectors contain a radioactive source they must be disposed of correctly.




Assessment Standard

Evidence Required

Evidence Produced

2.2 Describe an application


The application is linked to a key area of the course

Nuclear chemistry/ isotopes

Application stated

Smoke detectors

Appropriate chemistry knowledge is used to describe the application

Description of how a smoke detector works is given.

2.3 Describe a chemistry issue in terms of the effect on the environment/ society


The chemistry issue is linked to a key area of the course

Nuclear chemistry/ isotopes

A relevant issue is stated

Alpha particle, disposal

Appropriate chemistry knowledge is used to describe its effect

Nuclear equation given , alpha radiation, small amount used, correct disposal


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