1. Magnetic resonance imaging (MRI) is a diagnostic technique in which protons, in water and other molecules inside a patient, interact with a magnetic field.
(a) State the property of protons that allows them to be detected by MRI.
(b) State one advantage, other than reducing health risks, of using MRI rather than X-ray radiography.
2. (a) The mass spectrum of an unknown acidic compound, X, with empirical formula CH2O,is shown below.
(i) Determine the relative molecular mass, to the nearest integer, of the compound from the mass spectrum and deduce the formula of the molecular ion.
(ii) Deduce the formula of the fragment responsible for the peak at 45.
(iii) Deduce the formula of the fragment responsible for the peak at 29.
(b) The low-resolution 1H NMR spectrum of X shows four peaks. A simplified representation is shown alongside a table with relative peak areas.
(i) Identify the group responsible for the peak at D.
(ii) Suggest a possible structure for X.
(c) Infrared (IR) spectroscopy is widely used as a technique in analytical chemistry to show the presence of chemical bonds. Explain what happens at a molecular level during the absorption of IR radiation by the C–H bonds in an organic molecule.
3. Paper chromatography and thin-layer chromatography (TLC) can both be used to separate and analyse a mixture of amino acids.
(a) Compare the two techniques by completing the following table.
(b) State one advantage of using TLC rather than paper chromatography.
(c) Amino acids can be identified by their retention factor (Rf value). Calculate the Rf value of the amino acid, A, from the chromatogram below.
4. Aluminium salts are widely used in water treatment, but levels need to be continually monitored because high exposure to Al3+ ions may increase the risk of Alzheimer’s disease. A sample of drinking water was analysed using atomic absorption (AA) spectroscopy. A simplified diagram of the AA spectrometer is shown below.
(a) Outline the essential characteristics of the hollow cathode lamp.
(b) Describe the changes that the sample undergoes at Y and Z.
(c) The AA spectrometer was calibrated and the following results were obtained.
Draw a calibration curve on the grid provided and determine the concentration, in μg cm–3, of Al3+ ions in the unknown sample.