AQA GCSE Chemistry (8462), Higher tier · Chemical analysis › Identification of ions
Practise Flame emission spectroscopy. 12 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Required practical:Identifying ions (method, variables and exam tips)
Quick recall
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Name the piece of equipment used to produce and record the line spectrum of a sample in flame emission spectroscopy.
a spectroscope
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy3 marks
Flame emission spectroscopy is an instrumental method used to analyse metal ions in solutions. The sample is put into a flame and the light given out is passed through a spectroscope.
(a) What is the output from the spectroscope called? Tick (✓) one box.[1]
A chromatogram
A line spectrum
A precipitate
A reaction profile
(b) Give two things that the output can be used to find out about the metal ions in the solution.[2]
Show the answer and mark scheme
(a)Answer: A line spectrum
(b)
which metal ions are present / the identity of the metal ions
the concentration of the metal ions
Question 2Medium2 marks
Explain the similarity and the key difference between a flame test and flame emission spectroscopy.[2]
Show the answer and mark scheme
both rely on metal ions giving out light of characteristic colours / wavelengths when heated in a flame
flame emission spectroscopy uses an instrument to detect and measure the exact wavelengths and intensities present (allowing mixtures to be identified and concentrations to be measured), rather than relying on the human eye judging an overall colour
Question 3Hard5 marks
A scientist analyses a sample of pond water using flame emission spectroscopy and compares the spectrum with reference spectra for sodium, potassium and calcium ions. The sample's spectrum contains all of the reference lines for sodium, plus one extra line that does not match sodium, potassium or calcium.
(a) Explain what the extra line suggests about the sample.[2]
(b) The scientist also wants to find the concentration of sodium ions in the pond water. Describe how flame emission spectroscopy could be used to do this.[3]
Show the answer and mark scheme
(a)
the sample contains at least one other metal ion, in addition to sodium, that was not included in the scientist's reference spectra
the exact identity of this extra ion cannot be found without comparing it against further reference spectra for other metal ions
(b)
measure the intensity of a sodium line for several standard solutions of known sodium ion concentration
plot a calibration graph of intensity against concentration
measure the intensity for the pond water sample and read its concentration from the graph