BLSS Prelim P2 ans

2 BLS/PRELIM/2024/4E/CHEMISTRY/6092/02 Section A [70 marks] Answer all questions. 1 The formulae of some elements are given in the following list. Al Cu Fe H 2 Na O 2 Zn (a) Choose elements from the list to answer the questions. (i) Which element is used as a catalyst in the Haber process? Fe [1] (ii) Choose one element which shows both metallic and non-metallic character. H2 [1] (iii) Which element can be extracted from its ore by heating with carbon and is purified by electrolysis? Cu [1] (iv) Which element is produced at the graphite anode during electrolysis of aqueous sodium sulfate? O2 [1] (v) Which element is used for galvanizing? Zn [1] (b) (i) Which elements in the list are transition elements? Cu, Fe [1] (ii) Give three characteristic properties of transition elements. Form colored compounds. Have variable oxidation states in compounds. Are used as catalysts. [2] [Total: 8] 4E Chem Prelim 2024 P2 Answers

3 BLS/PRELIM/2024/4E/CHEMISTRY/6092/02 2 Read the information about the electrolysis of potassium chloride. Potassium chloride has a melting point of over 700 oC. Molten potassium chloride can be electrolysed. Chlorine gas forms at the anode. We might expect potassium metal to form at the cathode, but in practice, potassium is very soluble in molten potassium chloride. A solution of potassium in molten potassium chloride forms. This problem means that electrolysis cannot be used to extract potassium from potassium chloride. (a) The information contains an example of a compound and an example of a mixture. (i) Identify the compound and mixture in the information. compound potassium chloride mixture solution of potassium in molten potassium chloride [1] (ii) Explain the difference between a compound and a mixture. A compound is a PURE substance containing two or more ELEMENTS that are chemically combined in a FIXED RATIO while a mixture is made up of two or more SUBSTANCES that are NOT chemically combined and not in any fixed ratio. The ELEMENTS in a compound are combined in a FIXED RATIO while The COMPONENTS of a mixture can be mixed in any proportion. The physical and chemical properties of a compound are different from the elements it is made of while the chemical properties of a mixture are the same as those of its components. [any one] [1] (b) The electronic configuration of a potassium atom is 2,8,8,1. Complete Table 2.1 to show the electronic configuration of a potassium ion and a chloride ion. Table 2.1 Ion electronic configuration K+ 2,8