XMS SEC 3 WA2 2022 QP

3 6092/Chemistry/2022 WA2 Section A [5 marks] Answer all questions. Write your answers in the boxes provided at the end of the Section. 1 Copper is used in electrical wirings to conduct electricity. Why is copper able to conduct electricity? A Copper has a ‘sea’ of delocalised electrons. B Copper has free-moving ions. C Copper has a ‘sea’ of delocalised ions. D Copper has free-moving atoms. 2 Calcium phosphate is the main mineral found in human bones and teeth. What is the chemical formula of calcium phosphate? A CaPO3 B CaPO4 C Ca3(PO3)2 D Ca3(PO4)2 3 The following chromatogram was obtained by a student. What is the R f value of the spot marked ‘X’? A 8 3 + 8 B 3 3 + 8 C 3 + 8 8 D 3 8

4 6092/Chemistry/2022 WA2 4 A solid substance was found to be unable to conduct electricity. When pure water was used to dissolve the substance, the solution could conduct electricity. What could be the structure of the substance, and why can the solution conduct electricity? Structure Reason for being able to conduct electricity A giant metallic structure Water can conduct electricity. B giant metallic structure It has free-moving electrons. C giant ionic structure It has free-moving ions. D giant ionic structure Water can conduct electricity. 5 The following diagram shows a set -up used to obtain clean water from dirty river water in a rural village. Which method of separation is used to obtain clean water in this case? A using a separating funnel B filtration C distillation D evaporation Write your answers for Section A in the boxes below. 1. 2. 3. 4. 5. [Total: 5]

5 6092/Chemistry/2022 WA2 Section B [30 marks] Answer all questions. Write your answers in the spaces provided. B1 Use the list of substances to answer the questions. sulfur dioxide graphite oxygen sodium sulfate dry ice (a) (i) Which substance is ionic? ……………………………………………………………………………………… [1] (ii) Which substance has a giant molecular structure? ……………………………………………………………………………………… [1] (iii) Which two substances contain two elements from Group VI? ……………………………………………………………………………………… [1] (iv) If the substances above were mixed, which substance can be obtained by sublimation? ……………………………………………………………………………………… [1] (v) Which substance can conduct electricity in the solid state? ……………………………………………………………………………………… [1] (vi) Write down the chemical formula for one of the compounds. ……………………………………………………………………………………… [1] (b) Draw the ‘dot’-and-‘cross’ diagram for ammonia. Show outer electrons only. [2] [Total: 8 marks]

6 6092/Chemistry/2022 WA2 B2 Write down a method of separation used to obtain the underlined component of the mixture below. (a) (i) oil and water …………………………………………………………………………………………. [1] (ii) salt and oil …………………………………………………………………………………………. [1] (iii) sugar and water …………………………………………………………………………………………. [1] (b) The set-up below shows the apparatus used for distillation of a mixture of acetone and ethanol. The boiling point of acetone and ethanol are 56 oC and 78 oC respectively. (i) After heating the mixture from room temperature for some time, the thermometer reading stops increasing and remains at a constant temperature. What is the reading on the thermometer when the temperature is constant? …………………………………………………………………………………………. [1] (ii) Using arrows, show where water enters and exits the condenser. [1] (iii) Using the axes provided below, sketch a graph to show the change in temperature of the mixture against time. [2] [Total: 7 marks] temperature/ oC time/ min

7 6092/Chemistry/2022 WA2 B3 (a) Write the chemical equations for the following reactions. (i) Sodium metal reacts with water to form hydrogen gas and sodium hydroxide. …………………………………………………………………………………………. [1] (ii) Nitric acid reacts with calcium oxide to form calcium nitrate and water. …………………………………………………………………………………………. [1] (iii) Propene (C3H6) burn in oxygen to form carbon dioxide and water. …………………………………………………………………………………………. [1] (b) Draw the ‘dot’-and-‘cross’ diagram for calcium oxide. Show outer electrons. [2] [Total: 5] B4 Carbon is a highly versatile element that has many allotropes. Allotropes are different forms of the same element which includes diamond, fullerene, graphite and Single -Walled Carbon Nanotubes (SWCNT). Carbon atoms, having four valence electrons, have a preference for sharing electrons instead of transferring electrons to form a bond. Diamond occurs naturally underneath the Earth’s surface while fullerene, graphite and SWCNT can be made in a laboratory from a flat 2-dimensional honeycomb lattice of carbon atoms known as graphene. A schematic structure of how graphene can be made into fullerene, SWCNT and graphite is shown on the next page. Fullerene is formed when the carbon atoms are arranged in the form of spherical molecules. One of the most common fullerene is known as buckminsterfullerene, also known as buckyball, which is a molecule made of 60 carbon atoms. SWCNT can be visualised as one flat graphene sheet of carbon atoms rolled into a cylindrical shape while graphite can be visualised as the stacking of multiple graphene sheets. Each carbon atom in buckyball, SWCNT and graphite is bonded to three other carbon atoms. This would mean that these three structures have a delocalised electron per carbon atom that is able to conduct electricity.

8 6092/Chemistry/2022 WA2 Diamond is another allotrope of carbon with the following structure. Unlike the four allotropes above, each carbon atom in diamond is bonded to four other atoms. The physical properties of diamond, fullerene, graphite and SWCNT are shown in the table below. The electrical conductivity is measured in S/cm where high values reflect good electrical conductivity. carbon allotrope properties diamond buckyball graphite SWCNT electrical conductivity (S/cm) 0.001 0.00001 4000 1 000 000 relative electron movement speed low very low high very high melting point (oC) 4030 600 3600 3550 relative cost high very high low high solubility in organic solvents no yes no no flexibility no yes no yes graphene buckyball SWCNT graphite diamond

9 6092/Chemistry/2022 WA2 (a) Explain, in terms of electronic configuration, why carbon has a tendency to form molecules but not ions. ………………………………………………………………………………………………… ………………………………………………………………………………………………… [1] (b) (i) With reference to the table, state the relationship between the relative electron movement speed and electrical conductivity. …………………………………………………………………………………………. …………………………………………………………………………………………. [1] (ii) With reference to their structures, e xplain why SWCNT is a much better conductor of electricity than diamond. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. [3] (c) Scientists consider buckyball to have a simple molecular structure. (i) Give two pieces of evidence from the table that support this. …………………………………………………………………………………………. …………………………………………………………………………………………. [2] (ii) Using information from the passage, suggest the chemical formula of buckyball. …………………………………………………………………………………………. [1] (d) One useful application of carbon allotropes is in the development of solar panel cells that