8.8 Instrumental methods and flame emission spectroscopy
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Which is an advantage of instrumental methods over chemical tests?
Choose one answer.
Correct Not quite: the answer is They are more sensitive
Mark scheme
D
Model answer
D: instrumental methods are accurate, sensitive and rapid.
Explain how flame emission spectroscopy can identify the metal ions in a mixture.
Mark scheme
- each metal ion gives a unique line spectrum (1)
- compare the sample's lines with reference spectra; matching lines show the ions present (1)
Model answer
Each metal ion produces a unique pattern of lines. The lines in the sample's spectrum are compared with reference spectra, and any ion whose lines all appear is present.
Give one reason why flame emission spectroscopy is better than a flame test for a mixture of metal ions.
Mark scheme
- flame colours can mask each other / spectroscopy shows each ion's lines separately (1)
Model answer
In a flame test, one colour can hide another, but spectroscopy shows each ion's lines separately.
Describe how a calibration curve is used to find the concentration of sodium ions in a water sample.
Mark scheme
- measure intensity for solutions of known concentration (1)
- plot intensity against concentration (1)
- measure intensity of the sample and read the concentration from the graph (1)
Model answer
Measure the intensity for several solutions of known concentration and plot a calibration curve. Then measure the intensity of the sample and read its concentration from the curve.
Give two advantages of instrumental methods of analysis.
Mark scheme
any two from:
- accurate (1)
- sensitive (1)
- rapid (1)
Model answer
They are accurate and very sensitive.
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