Cambridge IGCSE Chemistry Laboratory Practical Book Answer

Answers to Cambridge IGCSE ® Chemistry Laboratory Practical Book Experimental skills and abilities Skills for scientific enquiry 1 (a) measuring cylinder (e) stopwatch (b) digital balance (f) digital timer (c) metre ruler (g) ruler (d) liquid in glass thermometer 2 (a) Time at least 10 oscillations with a stopwatch and divide the result by 10 to obtain the average time for one oscillation. (b) Weigh at least 20 pins on a balance and divide the result by 20 to obtain the average mass of one pin. 3 Device Accuracy metre ruler 1 mm vernier scale 0.1 mm stopwatch 0.5 s digital timer 1 ms digital balance typically 1 g or 0.1 g liquid in glass thermometer 1.0 °C 100 cm 3 measuring cylinder 1 cm 3 4 (a) 9.75 (b) 9.8 (c) 1 × 10 1 5 (a) (i) Effect of temperature on rate (ii) Light intensity, concentrations of solutions (iii) Manipulated variable Fixed variable Responding variable temperature light, concentration rate of reaction (b) 25 20 15 10 Temperature/°C 5 0 0 2 4 6 8 10 Rate of reaction (c) Increase in temperature will result in increase in rate of reaction. 1 Cambridge IGCSE Chemistry Laboratory Practical Book © Doug Wilford & Bryan Earl 2015

Answers to Cambridge IGCSE ® Chemistry Laboratory Practical Book Experimental skills and abilities Skills for scientific enquiry 1 (a) measuring cylinder (e) stopwatch (b) digital balance (f) digital timer (c) metre ruler (g) ruler (d) liquid in glass thermometer 2 (a) Time at least 10 oscillations with a stopwatch and divide the result by 10 to obtain the average time for one oscillation. (b) Weigh at least 20 pins on a balance and divide the result by 20 to obtain the average mass of one pin. 3 Device Accuracy metre ruler 1 mm vernier scale 0.1 mm stopwatch 0.5 s digital timer 1 ms digital balance typically 1 g or 0.1 g liquid in glass thermometer 1.0 °C 100 cm 3 measuring cylinder 1 cm 3 4 (a) 9.75 (b) 9.8 (c) 1 × 10 1 5 (a) (i) Effect of temperature on rate (ii) Light intensity, concentrations of solutions (iii) Manipulated variable Fixed variable Responding variable temperature light, concentration rate of reaction (b) 25 20 15 10 Temperature/°C 5 0 0 2 4 6 8 10 Rate of reaction (c) Increase in temperature will result in increase in rate of reaction. 1 Cambridge IGCSE Chemistry Laboratory Practical Book © Doug Wilford & Bryan Earl 2015

1 The particulate nature of matter Answers 1.1 Rate of diffusion of ammonia and hydrogen chloride Method 1 To ensure that it is a fair test. 2 It would be too difficult to deal with the gases. The gases would begin to diffuse before the experiment started. 3 Ammonia is toxic. Concentrated hydrochloric acid is corrosive. Results and calculations Students should be able to show that the ammonia particles (molecules) have moved along the tube at a faster rate than the hydrogen chloride particles (molecules). Conclusions 1 The longer the tube, the longer the time taken for the white cloud of ammonium chloride to form. This is because the rate of diffusion will be slower for both gases. 2 The greater the diameter of the tube, the longer the time taken for the white cloud to form. 3 Temperature of the laboratory – the higher the temperature the faster the time; concentration of the gases used – the higher their concentration the faster the time; pressure – the higher the room pressure the slower the time. 4 Hydrogen chloride end. 5 The hydrogen chloride molecules are heavier and therefore have the slower rate of diffusion, so do not travel as far along the tube as the ammonia particles. Evaluation The experiment could be repeated to gain an average times and rates. Extension The rate of diffusion is not the same as the speed of the particles. The speed of the particles will be much greater than the rate of diffusion. The reason is that the rate of diffusion is lower due to the random collisions between the particles which prevent the particles from travelling in straight lines. 1.2 Reaction of potassium iodide with lead(II) nitrate Method 1 Because the particles in both solids are vibrating about a fixed point. For the reaction to occur their particles need to be forced to collide with one another. Shaking causes this to happen. 2 In case, when you are shaking the tube, you hit a bench or other solid object. 3 So that there was no contamination of each chemical. Results A yellow tinge should be visible on the solid particles, which takes a long time to form. When the two colourless solutions are mixed, a yellow precipitate (solid) forms. If left, the yellow precipitate sinks to the bottom of the tube and a colourless solution is visible above it. 2 Cambridge IGCSE Chemistry Laboratory Practical Book © Doug Wilford & Bryan Earl 2015

1 The particulate nature of matter Answers 1.1 Rate of diffusion of ammonia and hydrogen chloride Method 1 To ensure that it is a fair test. 2 It would be too difficult to deal with the gases. The gases would begin to diffuse before the experiment started. 3 Ammonia is toxic. Concentrated hydrochloric acid is corrosive. Results and calculations Students should be able to show that the ammonia particles (molecules) have moved along the tube at a faster rate than the hydrogen chloride particles (molecules). Conclusions 1 The longer the tube, the longer the time taken for the white cloud of ammonium chloride to form. This is because the rate of diffusion will be slower for both gases. 2 The greater the diameter of the tube, the longer the time taken for the white cloud to form. 3 Temperature of the laboratory – the higher the temperature the faster the time; concentration of the gases used – the higher their concentration the faster the time; pressure – the higher the room pressure the slower the time. 4 Hydrogen chloride end. 5 The hydrogen chloride molecules are heavier and therefore have the slower rate of diffusion, so do not travel as far along the tube as the ammonia particles. Evaluation The experiment could be repeated to gain an average times and rates. Extension The rate of diffusion is not the same as the speed of the particles. The speed of the particles will be much greater than the rate of diffusion. The reason is that the rate of diffusion is lower due to the random collisions between the particles which prevent the particles from travelling in straight lines. 1.2 Reaction of potassium iodide with lead(II) nitrate Method 1 Because the particles in both solids are vibrating about a fixed point. For the reaction to occur their particles need to be forced to collide with one another. Shaking causes this to happen. 2 In case, when you are shaking the tube, you hit a bench or other solid object. 3 So that there was no contamination of each chemical. Results A yellow tinge should be visible on the solid particles, which takes a long time to form. When the two colourless solutions are mixed, a yellow precipitate (solid) forms. If left, the yellow precipitate sinks to the bottom of the tube and a colourless solution is visible above it. 2 Cambridge IGCSE Chemistry Laboratory Practical Book © Doug Wilford & Bryan Earl 2015

Answers Conclusions 1 A yellow tinge on the solid particles. 2 Two colourless solutions reacted to give another colourless solution and a yellow precipitate. 3 The reaction between the solutions. 4 The reaction in Procedure 2 occurred faster because, in solutions, the particles are able to move relative to one another. This allows them to collide more frequently with one another, causing the reaction to occur more rapidly. 5 Colourless. Evaluation In Procedure 1, the same mass, or, better, the same number of moles of each were used. In Procedure 2, the same volume of each solution, of the same concentration, could have been used. Extension Any one of: 1 The shaking could have been more vigorous, resulting in more collisions, and more successful collisions. 2 The solids could have been more finely crushed. With a larger surface area, more collisions and more successful collisions would occur. 3 The experiment could have been carried out at a higher temperature, so particles have more kinetic energy. More collisions and more successful collisions would occur. 1.3 Sublimation of iodine Method 1 Iodine is harmful. Its fumes are dangerous for the environment. 2 To prevent the majority of the iodine vapour from escaping. The iodine vapour returns to a solid on the large, cool surface area given by the glass wool. 3 No. The pressure build up in the tube when the iodine solid changed to iodine vapour would have caused it to be blown off. Results Much of the iodine will have moved from the bottom of the tube to the top. The black/violet solid iodine sublimed on heating to give violet iodine vapour. The iodine vapour returned to its solid form when it reached the cooler parts of the tube. Conclusions 1 Black/violet. 2 Violet. 3 At the top of the tube. The top of the tube is cooler than the bottom and so the iodine vapour sublimes to iodine solid. Evaluation A longer tube could have been used. Extension Any two from: arsenic, carbon and phosphorus (red). 3 Cambridge IGCSE Chemistry Laboratory Practical Book © Doug Wilford & Bryan Earl 2015

Conclusions Answers 1 A yellow tinge on the solid particles. 2 Two colourless solutions reacted to give another colourless solution and a yellow precipitate. 3 The reaction between the solutions. 4 The reaction in Procedure 2 occurred faster because, in solutions, the particles are able to move relative to one another. This allows them to collide more frequently with one another, causing the reaction to occur more rapidly. 5 Colourless. Evaluation In Procedure 1, the same mass, or, better, the same number of moles of each were used. In Procedure 2, the same volume of each solution, of the same concentration, could have been used. Extension Any one of: 1 The shaking could have been more vigorous, resulting in more collisions, and more successful collisions. 2 The solids could have been more finely crushed. With a larger surface area, more collisions and more successful collisions would occur. 3 The experiment could have been carried out at a higher temperature, so particles have more kinetic energy. More collisions and more successful collisions would occur. 1.3 Sublimation of iodine Method 1 Iodine is harmful. Its fumes are dangerous for the environment. 2 To prevent the majority of the iodine vapour from escaping. The iodine vapour returns to a solid on the large, cool surface area given by the glass wool. 3 No. The pressure build up in the tube when the iodine solid changed to iodine vapour would have caused it to be blown off. Results Much of the iodine will have moved from the bottom of the tube to the top. The black/violet solid iodine sublimed on heating to give violet iodine vapour. The iodine vapour returned to its solid form when it reached the cooler parts of the tube. Conclusions 1 Black/violet. 2 Violet. 3 At the top of the tube. The top of the tube is cooler than the bottom and so the iodine vapour sublimes to iodine solid. Evaluation A longer tube could have been used. Extension Any two from: arsenic, carbon and phosphorus (red). 3 Cambridge IGCSE Chemistry Laboratory Practical Book © Doug Wilford & Bryan Earl 2015