AQA A-level CHEMISTRY Paper 2 Organic and Physical Chemistry 2020 QP. Phosphinate ions (H2PO2 – ) react with hydroxide ions to produce hydrogen gas as shown. H2PO2 – + OH− → HPO3 2– + H2 A student completed an experiment to determine the initial rate of this reaction. The student used a solution containing phosphinate ions and measured the volume of hydrogen gas collected every 20 seconds at a constant temperature. Figure 1 shows a graph of the student’s results.