Chemistry C2

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The properties of polymers depend on what they are made from and the conditions under which they are made. For example, low density (LD) and high density (HD) poly(ethene) are produced using different catalysts and reaction conditions.
Thermosoftening polymers consist of individual, tangled polymer chains. Thermosetting polymers consist of polymer chains with cross-links between them so that they do not melt when they are heated.
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Nanoscience refers to structures that are 1–100 nm in size, of the order of a few hundred atoms.
Nanoparticles show different properties to the same materials in bulk and have a high surface area to volume ratio, which may lead to the development of new computers, new catalysts, stronger and lighter construction materials, and new cosmetics
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The total number of protons and neutrons in an atom is called its mass number.
Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element.
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The relative atomic mass of an element (Ar ) compares the mass of atoms of the element with the 12C isotope. It is an average value for the isotopes of the element.
The relative formula mass (Mr ) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.
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The relative formula mass of a substance, in grams, is known as one mole of that substance
Elements and compounds can be detected and identified using instrumental methods. Instrumental methods are accurate, sensitive and rapid and are particularly useful when the amount of a sample is very small.
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Chemical analysis can be used to identify additives in foods. Artificial colours can be detected and identified by paper chromatography.
Gas chromatography allows the separation of a mixture of compounds
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The time taken for a substance to travel through the column can be used to help identify the substance
The output from the gas chromatography column can be linked to a mass spectrometer, which can be used to identify the substances leaving the end of the column
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The mass spectrometer can also give the relative molecular mass of each of the substances separated in the column.
The molecular mass is given by the molecular ion peak.
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Different substances, carried by a gas, travel through a column packed with a solid material at different speeds, so that they become separated
The number of peaks on the output of a gas chromatograph shows the number of compounds present
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The position of the peaks on the output indicates the retention time
A mass spectrometer can identify substances very quickly and accurately and can detect very small quantities.
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Card 2

Front

Nanoparticles show different properties to the same materials in bulk and have a high surface area to volume ratio, which may lead to the development of new computers, new catalysts, stronger and lighter construction materials, and new cosmetics

Back

Nanoscience refers to structures that are 1–100 nm in size, of the order of a few hundred atoms.

Card 3

Front

Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element.

Back

Preview of the back of card 3

Card 4

Front

The relative formula mass (Mr ) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.

Back

Preview of the back of card 4

Card 5

Front

Elements and compounds can be detected and identified using instrumental methods. Instrumental methods are accurate, sensitive and rapid and are particularly useful when the amount of a sample is very small.

Back

Preview of the back of card 5
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