C2.3 How Much?
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What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
1/2000
What does the mass number mean?
The number of protons + the number of neutrons
What is an isotope?
Atoms with the same number of protons and electrons but different number of neutrons
What is relative atomic mass?
The mass of an atom compared to 1/12 of an atom of carbon-12
What is relative atomic mass measured in?
Grams
What is the relative formula mass (Mr) of CO2
12 + 16 + 16 = 44
What is the relative formula mass (Mr) of MgO?
24 + 16 = 40
What is the percentage by mass of magnesium in magnesium oxide?
24 / 40 x 100 = 60%
Give two benefits of using instrumental methods such as gas chromatography?
Highly accurate/Sensitive Quicker Can detect small samples
Give two disadvantages of using instrumental methods such as gas chromatography?
Very expensive Require specialist training to interpret Can only identify samples by comparing with data of known substances
In what part is the relative molecular mass of a substance measured?
The mass spectrometer
What is the retention time?
The time from when a substance enters a gas chromatogram, to when it leaves.
Describe the similarities and differences between atoms of oxygen-16 and oxygen-18
Both have the same number of protons (8) Both have the same number of electrons (8) Oxygen-18 has 10 neutrons Oxygen-16 has 8 neutrons Have different number of neutrons