This reaction is part of a water-treatment process. Fig. 1 shows acidic water entering a tank containing calcium carbonate granules. The outlet water is tes...
Question 1 Report
This reaction is part of a water-treatment process. Fig. 1 shows acidic water entering a tank containing calcium carbonate granules. The outlet water is tested before it enters a reservoir. The granules react slowly with acid, producing calcium ions, water and carbon dioxide. A mesh keeps the solid granules inside the tank.
(a) Give the name of the reaction occurring in the tank. [1]
(b) Use the information to give the gas released. [1]
(c) Describe why the pH of the outlet water is higher than the pH of the incoming water. [2]
This reaction is used by a metal workshop to identify an unlabelled cleaning liquid. Fig. 1 shows a small magnesium ribbon placed into the liquid in a test tube. Bubbles form and a lit splint held at the mouth gives a squeaky pop. The workshop has hydrochloric acid, sodium hydroxide solution and water in unlabelled bottles. The technician wears eye protection because the liquid may splash during the reaction.
(a) Give the name of the gas tested by the squeaky pop. [1]
(b) Use the observation to give the type of cleaning liquid. [1]
(c) Describe the test-tube safety precaution shown in Fig. 1 that reduces injury from splashes. [2]
Answer Details
Water-treatment tank
(a) The reaction in the tank is neutralisation. [1]
(b) The gas released is carbon dioxide. [1]
(c) Calcium carbonate reacts with and removes acid from the incoming water. The water therefore becomes less acidic, so its pH rises. [2]
Cleaning-liquid identification
(a) The squeaky-pop test identifies hydrogen. [1]
(b) The cleaning liquid is an acid, specifically hydrochloric acid from the listed possibilities. Magnesium reacting with acid produces hydrogen. [1]
(c) The test tube should be held or pointed away from people. This prevents splashing liquid being projected towards somebody's face or body. [2]
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