Cl₂(aq) + KBr(aq) A Br₂(aq) + KCl(aq) B Fig. 1 shows a laboratory test in which chlorine water is shaken with colourless potassium bromide solution. A stopp...
Question 1 Report
Fig. 1 shows a laboratory test in which chlorine water is shaken with colourless potassium bromide solution. A stopper is fitted before the test tube is shaken. A second tube contains bromine water and potassium chloride solution. The student uses the colour change to compare the reactivity of halogens.
(a) Name the type of reaction taking place when chlorine is added to potassium bromide solution. [1]
(b) Complete the ionic equation.
Cl2 + 2Br- → 2Cl- + ______ [1]
(c) Suggest the colour seen if bromine is formed. [1]
(d) Use the results to state which is more reactive, chlorine or bromine. [2]
Fig. 1 shows a sealed food packet flushed with nitrogen before it is closed. Nitrogen is not a Group 0 element, but the company is considering using argon instead. Both gases reduce the amount of oxygen around the food. The packet contains crisps made with vegetable oil.
(a) Name the Group 0 gas that could be used instead of nitrogen. [1]
(b) Suggest why oxygen is removed from the packet. [1]
(c) Give one property of argon that makes it appropriate for this use. [1]
(d) What name is given to reactions in which a substance combines with oxygen? [2]
Answer Details
Halogen displacement
- Chlorine added to potassium bromide is a displacement reaction. [1]
- \[\mathrm{Cl_2+2Br^-\rightarrow2Cl^-+Br_2}\] The missing product is \(\mathrm{Br_2}\). [1]
- If bromine forms, the colour is orange or orange-brown. [1]
- Chlorine is more reactive than bromine because it displaces bromine from bromide ions. In electron terms, chlorine gains electrons from bromide ions. [2]
Food packet
- The Group 0 gas that could be used is argon. [1]
- Oxygen is removed to prevent the oil oxidising and becoming rancid. [1]
- Argon is suitable because it is unreactive or inert. [1]
- Reactions in which a substance combines with oxygen are called oxidation. Oxidation is the gain of oxygen. [2]
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