(2) The chemical properties of acids require metals, metal oxides, etc. , not shown in the figure, so it won't be ①; The purification of crude salt requires an alcohol lamp, which is not shown in the figure, so it can't be ②. Calcium carbonate and dilute hydrochloric acid are needed to prepare carbon dioxide in the laboratory. The instruments used are large test tubes, double-hole rubber plugs, long-necked funnels, gas cylinders and matches, all of which are shown in the figure, so it is ③. To prepare a solution with a certain solute mass fraction, it is necessary to use a tray balance and a measuring cylinder, which are not shown in the figure, so it is not ④, so fill in: ③;
(3) As can be seen from the figure, when the liquid medicine is added to the test tube, the cork is not reversed. Check whether the carbon dioxide is completely collected and the burning match cannot reach into the gas container, so fill in: ②, ④;
(4) Operation analysis of checking the air tightness of the device: put the catheter mouth into the water, hold the test tube by hand, and observe that bubbles emerge from the catheter mouth in the beaker, which shows that the device has good air tightness; Therefore, filling: bubbles emerge from the mouth of the catheter;
(5) The oxygen produced by mixing hydrogen peroxide solution and manganese dioxide in the laboratory does not need to be heated, and the density of oxygen is higher than that of air, so it can be collected by upward exhaust method; So we use: test tube, iron frame, single-hole rubber plug with catheter, gas container. Therefore, it is: ABCE. ..