2019年11月IB化学SL真题下载-Paper3
1. A student investigated how the type of acid in acid deposition affects limestone, a building material mainly composed of calcium carbonate.
The student monitored the mass of six similarly sized pieces of limestone. Three were placed in beakers containing 200.0 cm3 of 0.100 mol dm−3 nitric acid, HNO3 (aq), and the other three in 200.0 cm3 of 0.100 mol dm−3 sulfuric acid, H2SO4 (aq).
The limestone was removed from the acid, washed, dried with a paper towel and weighed every day at the same time and then replaced in the beakers.
The student plotted the mass of one of the pieces of limestone placed in nitric acid against time.
(a) Draw a best-fit line on the graph.
(b) (i) Determine the initial rate of reaction of limestone with nitric acid from the graph.Show your working on the graph and include the units of the initial rate.
(ii) Explain why the rate of reaction of limestone with nitric acid decreases and reaches zero over the period of five days.
(iii) Suggest a source of error in the procedure, assuming no human errors occurred and the balance was accurate.
(c) The student hypothesized that sulfuric acid would cause a larger mass loss than nitric acid.
(i) Justify this hypothesis.
(ii) The student obtained the following total mass losses.
She concluded that nitric acid caused more mass loss than sulfuric acid, which did not support her hypothesis.
Suggest an explanation for the data, assuming that no errors were made by the student.
2. Ethanol was electrolysed at different voltages. The products at the anode, ethanoic acid, ethanal and carbon dioxide, were collected and analysed.
The percentages of products obtained using three different catalysts mounted on a carbon anode, platinum (Pt/C), platinum and ruthenium alloy (PtRu/C) and platinum and tin alloy (PtSn/C) are shown.
(a) (i) Describe the effect of increasing the voltage on the chemical yield of:
Ethanal using Pt/C:
Carbon dioxide using PtRu/C:
(ii) Determine the change in the average oxidation state of carbon.
From ethanol to ethanal:
From ethanol to carbon dioxide:
(iii) List the three products at the anode from the least to the most oxidized.
(b) Deduce, giving your reason, which catalyst is most effective at fully oxidizing ethanol.
2019年11月IB化学SL真题余下省略！
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