Question 1: Chlorine is a halogen element with the symbol Cl and atomic number 17. It is commonly used in disinfectants and bleach. Unlike some gases, Chlorine is toxic and has a pungent smell. Explain why Chlorine gas is considered a halogen and describe one key property that makes it useful in water treatment.

Answer: Chlorine is a halogen because it is in Group 17 of the periodic table. Its key property is its ability to disinfect water by killing bacteria and other pathogens.

Question 1: Describe the colour, smell, and solubility of Chlorine gas.

Answer: Chlorine gas is greenish-yellow in colour, has a pungent smell, and is soluble in water.

Question 2: Which common reagent is used to test for the presence of Chlorine gas? What is the observable result?

Answer: A damp litmus paper test; Chlorine turns moist litmus paper red and then bleaches it to white.

Question 3: Multiple Choice: Which of the following is a characteristic reaction of Chlorine with water?

Answer: Formation of hydrochloric acid and hypochlorous acid

Question 1: Explain the chemical basis for using damp litmus paper to identify Chlorine gas.

Answer: Chlorine is an oxidising gas that bleaches the dye in litmus paper and turns it white; it also reacts with moisture to produce hydrochloric acid, which further acidifies the paper.

Question 2: Describe what happens when Chlorine gas reacts with an aqueous solution of sodium hydroxide.

Answer: Chlorine reacts with sodium hydroxide to produce sodium chloride and sodium hypochlorite, which is used in bleach.

Question 1: Design a simple experiment to test for Chlorine gas using litmus paper. Include the variables involved and safety precautions.

Answer: To test for Chlorine, expose a damp litmus paper to the suspected gas in a well-ventilated area, wearing gloves and eye protection. The independent variable is the presence of Chlorine; the dependent variable is the change in litmus paper colour. Ensure the gas source is contained and handle all reagents with care to prevent inhalation or contact.

Question 1: A sample of gas reacts with moisture and turns moist litmus paper white. What gas could this be and why?

Answer: It could be Chlorine because it bleaches litmus paper and reacts with moisture to form hydrochloric acid.

Question 2: In a water treatment plant, Chlorine is added to disinfect the water. Explain how this process works at the molecular level.

Answer: Chlorine dissolves in water and reacts to form hydrochloric acid and hypochlorous acid, which are powerful oxidising agents. These acids attack the cell walls of bacteria and viruses, destroying their ability to reproduce and thus disinfecting the water.

Question 1: Describe one way in which Chlorine is used in industry outside of water treatment, and mention one safety concern associated with its use.

Answer: Chlorine is used in the production of plastics like PVC. A safety concern is that Chlorine gas is toxic and can cause respiratory problems if inhaled in high concentrations.