AQA A-Level Chemistry Topic 1 – Complete Solutions & Exam Q&A

AQA A-LEVEL CHEMISTRY TOPIC 1 - EXAM
QUESTIONS WITH COMPLETE SOLUTIONS.


Calculate the relative atomic mass...
Explain why the value you have calculated is slightly
different from the relative atomic mass given in the
periodic table. - correct answer - The Ar in the periodic
table takes into account the other isotopes.


Deduce which of Na+ and Mg 2+ is the smaller ion.
Explain your answer. (2 marks) - correct answer - - Mg
2+ is the smaller ion.
- they both have the same number of electrons but Mg
2+ has more protons


Define the term mass number of an atom - correct
answer - number of protons plus number of neutrons in
the nucleus


Describe how ions are formed in a time of flight mass
spectrometer. (2 marks) - correct answer - - a high
voltage is applied to a sample in a polar solvent
- the atoms gain protons and become positive ions

, Explain how ions are accelerated, detected and have their
abundance determined in a TOF mass spectrometer. (3
marks) - correct answer - - accelerated towards a
negatively charged plate
- detected by gaining electrons
- abundance determined by the size of the current flowing
in the detector


Explain how the detector in a mass spectrometer enables
the abundance of an isotope to be measured. - correct
answer - - ions hit the detector and cause a current to
flow
- bigger current = higher abundance


Explain why it is necessary to ionise molecules when
measuring their mass in a TOF mass spectrometer. (2
marks) - correct answer - - only ions will be accelerated
by an electric field
- also so that they produce a current when they hit the
detector


Explain why sodium has a lower melting point than
magnesium. - correct answer - - sodium has fewer
protons
- smaller attraction between nucleus and delocalised
electrons