Chemical bonding

Chemical bonding - Atomic structure and Chemical Bonding 97...

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Atomic structure and Chemical Bonding p. 1 A student used the following experimental set-up to study the migration of ions. The student placed a drop of potassium dichromate solution at A and a drop of a deep blue solution at C. It is known that the two solutions do not react and the deep blue colour of the solution at C is due to the cation present. (i) Write the formula of the ion responsible for the orange colour of potassium dichromate. (ii) Why was the filter paper moistened with sodium sulphate solution? (iii) An electric current was passed through the circuit for some time. (1) What would be the colour change at A? (2) What would be the colour change at B? Explain your answer. (iv) Using the same apparatus and materials, suggest how you could show that the colour changes in (iii) are NOT due to diffusion. Lithium is a Group I element in the Periodic Table. It occurs naturally in two isotopic forms. The relative abundance of the each of these isotopes is shown in the table below: Isotope 6 Li 7 Li Relative abundance (%) 7.4 92.6 (a) What is the meaning of the term „isotope‟? (b) Calculate the relative atomic mass of lithium. (c) A piece of freshly cut lithium metal is placed in air. (i) What would be observed on the surface of the metal after some time? Write the relevant chemical equation. (ii) Draw the electronic diagram of the product in (i), showing electrons in the outermost shells only. (6 marks) Both carbon and silicon are Group IV elements in the Periodic Table. The diagrams below show the structures of dry ice (solid carbon dioxide) and quartz (a form of silicon dioxide):
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Atomic structure and Chemical Bonding p. 2 i. With reference to the structures of the two substances, explain why quartz is a solid which melts at a high temperature, while carbon dioxide is a gas at room temperature. ii. With the help of a labeled diagram, suggest how to show experimentally that dry ice sublimes to give gaseous carbon dioxide. iii. Sand (an impure form of quartz) and limestone are raw materials used for making glass. (1) Name the main chemical constituent of limestone. (2) Suggest ONE reason why glass had been used by mankind for a long time. (3) Suggest ONE reason why glass bottles are preferred to plastic bottles for the storage of champagne. With the help of electronic diagrams, describe the formation of magnesium chloride and tetrachloromethane from atoms of relevant elements. State, with explanation, which of the two compounds has a higher melting point. (9 marks) Six compounds are classified into two groups as shown in the table below: Gas Solid Ammonia Carbon dioxide Nitrogen dioxide Iron(III) oxide Magnesium oxide Potassium oxide Reclassify these compounds into two groups according to a. one of their physical properties, and b. one of their chemical properties.
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Chemical bonding - Atomic structure and Chemical Bonding 97...

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