Chemistry unit 2 topic 3

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Mass & atomic no.
Mass number – top number - total number of protons and neutrons in an atom. Atomic number - bottom number - number of protons
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Isotopes
Atoms of the same element with different numbers of neutrons are called isotopes.
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Ars
relative atomic masses, the Ar of an element in grams is called one mole of atoms of the element. E.g – Ar of Ca is 40
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Mrs
relative formula mass of a substance found by adding up the relative atomic masses in its formula e.g – Mr of CaCl2 = 40+ (35.5X2)= 111
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What is the mass of one mole of Soduim hydroxide? Ars: Na=23, O=16, H=1?
40g
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Percentages
What is the percentage of carbon in CO2? – Ars: C=12, O=16. Mr of CO2 = 12 + (16X2) =44. (12/24)X100 = 27.3%
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Empirical formula
simplest ratio of the atoms or ions in a compound. In covalent compounds it is not always the same as the molecular formula (ethane C2H6, but empirical formula CH3) n=m/Mr – number of moles =mass / relative atomic mass
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What is the empirical formula of the hydrocarbon that contains 80% carbon?
-
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% Yield – actual mass / theoretical mass X 100
reasons for not getting 100% yield – reaction incomplete / reversible, reactant impure, product lost on equipment or to surroundings, side reactions.
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Analysing substances
foods can be checked by chemical analysis to ensure any additives are safe. These methods include paper chromatography and mass spectrometry
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Modern instrumental methods of analysis
rapid, accurate and sensitive. Computers process the data giving meaningful results almost instantly. Equipment usually expensive + training is needed for it.
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Gas chromatography
Mixture carried by gas through long column, packed with particles of a solid, individual compounds travel different speeds through column so come out different times.
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The amount of substance leaving the column at different times is recorded against time and shows number of compounds in the mixture and their retention times.
Their retention times can be compared with the results for known compounds to help identify the compounds in the mixture.
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The output from gas chromatography can be linked to a mass spectrometer
gives further data that a computer can use quickly to identify the individual compounds.
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A mass spectrometer can give the molecular mass of a compound
For an individual compound the peak ith the largest mass corresponds to an ion with just 1 electron removed. This peak is known as the molecular ion peak and is furthest to the right on the spectrum.
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Other cards in this set

Card 2

Front

Atoms of the same element with different numbers of neutrons are called isotopes.

Back

Isotopes

Card 3

Front

relative atomic masses, the Ar of an element in grams is called one mole of atoms of the element. E.g – Ar of Ca is 40

Back

Preview of the back of card 3

Card 4

Front

relative formula mass of a substance found by adding up the relative atomic masses in its formula e.g – Mr of CaCl2 = 40+ (35.5X2)= 111

Back

Preview of the back of card 4

Card 5

Front

40g

Back

Preview of the back of card 5
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