AQA A-level Chemistry Topic 1 - Exam
Questions
Two peaks were observed at m/z 104 and 118. Outline how a TOF mass spectrometer is able to separate
these two species to give two peaks. (4 marks) - Answer--The ions are accelerated using an electric field
-so they all have the same kinetic energy.
-The positive ions with m/z of 104 travel faster as they have a lighter mass
- so reach the detector first
Which of these atoms has the largest atomic radius?
Ar, Cl, Mg, Na (1 mark) - Answer-Na
as the number of protons increases, the atomic radius decreases
Deduce which of Na+ and Mg 2+ is the smaller ion. Explain your answer. (2 marks) - Answer-- Mg 2+ is
the smaller ion.
- they both have the same number of electrons but Mg 2+ has more protons
Explain why the first ionisation energy of sulfur is less than that of phosphorus. (2 marks) - Answer-- the
electrons in one of the 3p orbitals of S are paired
- paired electrons repel so less energy needed to remove one of them
Describe how ions are formed in a time of flight mass spectrometer. (2 marks) - Answer-- a high voltage
is applied to a sample in a polar solvent
- the atoms gain protons and become positive ions
, Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer.
(2 marks) - Answer-- only ions will be accelerated by an electric field
- also so that they produce a current when they hit the detector
Explain how ions are accelerated, detected and have their abundance determined in a TOF mass
spectrometer. (3 marks) - Answer-- accelerated towards a negatively charged plate
- detected by gaining electrons
- abundance determined by the size of the current flowing in the detector
This question is about the periodicity of the group 3 elements.
State and explain the general trend in first ionisation energy across period 3. (4 marks) - Answer-- the
first ionisation energy across period 3 increases
- because the nuclear charge increases
- so there's a stronger attraction between the nucleus and outer electron
- but same shielding by inner shells
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. - Answer-The Ar in the periodic table takes into account the other isotopes.
State why isotopes of an element have the same chemical properties - Answer-same number of
electrons in the outer shell
State one reason why particles with the same mass and velocity can be deflected by different amounts
in the same magnetic field. - Answer-different charges
Explain how the detector in a mass spectrometer enables the abundance of an isotope to be measured.
- Answer-- ions hit the detector and cause a current to flow
Questions
Two peaks were observed at m/z 104 and 118. Outline how a TOF mass spectrometer is able to separate
these two species to give two peaks. (4 marks) - Answer--The ions are accelerated using an electric field
-so they all have the same kinetic energy.
-The positive ions with m/z of 104 travel faster as they have a lighter mass
- so reach the detector first
Which of these atoms has the largest atomic radius?
Ar, Cl, Mg, Na (1 mark) - Answer-Na
as the number of protons increases, the atomic radius decreases
Deduce which of Na+ and Mg 2+ is the smaller ion. Explain your answer. (2 marks) - Answer-- Mg 2+ is
the smaller ion.
- they both have the same number of electrons but Mg 2+ has more protons
Explain why the first ionisation energy of sulfur is less than that of phosphorus. (2 marks) - Answer-- the
electrons in one of the 3p orbitals of S are paired
- paired electrons repel so less energy needed to remove one of them
Describe how ions are formed in a time of flight mass spectrometer. (2 marks) - Answer-- a high voltage
is applied to a sample in a polar solvent
- the atoms gain protons and become positive ions
, Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer.
(2 marks) - Answer-- only ions will be accelerated by an electric field
- also so that they produce a current when they hit the detector
Explain how ions are accelerated, detected and have their abundance determined in a TOF mass
spectrometer. (3 marks) - Answer-- accelerated towards a negatively charged plate
- detected by gaining electrons
- abundance determined by the size of the current flowing in the detector
This question is about the periodicity of the group 3 elements.
State and explain the general trend in first ionisation energy across period 3. (4 marks) - Answer-- the
first ionisation energy across period 3 increases
- because the nuclear charge increases
- so there's a stronger attraction between the nucleus and outer electron
- but same shielding by inner shells
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. - Answer-The Ar in the periodic table takes into account the other isotopes.
State why isotopes of an element have the same chemical properties - Answer-same number of
electrons in the outer shell
State one reason why particles with the same mass and velocity can be deflected by different amounts
in the same magnetic field. - Answer-different charges
Explain how the detector in a mass spectrometer enables the abundance of an isotope to be measured.
- Answer-- ions hit the detector and cause a current to flow
