C2 - Mass, Moles & Analysis
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What is the mass number of an atom?
The number of protons and neutrons in the nucleus.
What is the atomic number of an atom?
The number of protons an atom has.
What are isotopes?
Atoms with different numbers of neutrons.
What is the relative mass of a proton and neutron?
1
What is the relative mass of an electron?
1/1836
What is the relative formula mass of a compound?
The sum of the relative atomic mass of all of the atoms.
What is the mass of a mole of carbon, oxygen and iron?
• 12g • 16g • 56g
How is the percentage mass of an element in a compound found?
(mass of element / total mass of compound) x 100
How is the empirical formula found?
Simplest ratio of moles.
How is the number of moles of an element in a compound found?
mass of the element / relative atomic mass
What is the yield of a chemical reaction?
How much product was made.
How is percentage yield calculated?
(amount produced / maximum amount possible) x 100
Give five reasons why yield is rarely 100%.
• The reaction may be reversible. • Some reactants may give unexpected products. • The product may be lost in the apparatus. • The reactants may not be completely pure. • It may be difficult to separate products.
Why is it important to maximise yield?
• In order to produce less waste. • Reduce energy usage. • Conserve limited resources. • Reduces pollution.
What is a reversible reaction?
The products of the reaction can react to make the original reactants.
How are reversible reactions represented?
With the ⇌ symbol.
What are E numbers?
European food additive code.
How does paper chromatography work?
Some compounds in a mixture dissolve better than others in particular solvents.
Give three advantages of using instrumental analysis.
• They are highly accurate and sensitive. • They are quicker. • They enable very small samples to be analysed.
Give three disadvantages of instrumental analysis.
• It is usually very expensive. • It takes special training to use. • It gives results that can only be interpreted by comparison with known substance data.
What is gas spectrometry?
Separating compounds that are easily vaporised.
What is the mass spectrometer?
The instrument that identifies compounds.
Explain gas chromatography.
• The sample mixture is vaporised. • A carrier gas moves the vapour through the coiled column. • The compounds have different attractions to the material in the column. The compounds that have the stronger attractions have a longer retention time.
What is the molecular ion peak?
The peak with the largest mass which is shown at the end.