Навчальне дослідження 8. Дослідження електропровідності речовин і розчинів — Transcript

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1. 0:04Greetings, dear students. Have you ever
2. 0:08wondered why some substances conduct
3. 0:10electric current while others do not?
4. 0:14To answer this question, we will
5. 0:15conduct an investigation into the
6. 0:17electrical conductivity of various
7. 0:19substances and their aqueous solutions.
8. 0:21We will compare the results and find
9. 0:24out what role ions play in conducting
10. 0:26electric current. I suggest you not
11. 0:29only observe but also predict the
12. 0:31result before each experiment. Try to
13. 0:35explain whether the light bulb will
14. 0:37turn on, and check your hypothesis
15. 0:39after the experiment. So, please open
16. 0:42your notebooks and write down the topic
17. 0:44: investigation of the electrical
18. 0:46conductivity of substances and
19. 0:47solutions. Objective: to experimentally
20. 0:51investigate the electrical conductivity
21. 0:53of certain substances and their aqueous
22. 0:56solutions. To establish the connection
23. 0:59between electrical conductivity and the
24. 1:01presence of mobile charged particles.
25. 1:04Equipment and materials. A device for
26. 1:08determining electrical conductivity
27. 1:10with a power source, electrodes, and a
28. 1:12light bulb. Distilled water, sugar,
29. 1:16citric acid, alkali, sodium hydroxide,
30. 1:19copper sulfate, hydrochloric acid
31. 1:22solution, glassware. Procedure. First,
32. 1:28draw a table in which you will record
33. 1:30the results of the research. Experiment
34. 1:36one. Distilled water. Let's start our
35. 1:39investigation with distilled water. It
36. 1:41contains very few ions, so it conducts
37. 1:44electric current extremely poorly. We
38. 1:47immerse the electrodes in distilled
39. 1:49water and observe the light bulb. As we
40. 1:54can see, the light bulb does not light
41. 1:56up. This means that the electric
42. 1:59current in our experiment is
43. 2:00insufficient for it to light up.
44. 2:03Distilled water has extremely low
45. 2:05electrical conductivity, so it is
46. 2:07practically considered a dielectric.
47. 2:10Experiment two. Sugar. Now let's check
48. 2:13the electrical conductivity of dry
49. 2:15sugar. Sugar belongs to molecular
50. 2:18substances. Its particles are
51. 2:20electrically neutral molecules. which
52. 2:23cannot freely carry an electric charge.
53. 2:26We check the sample using the device.
54. 2:33The light bulb does not light up. Thus,
55. 2:35under normal conditions, dry sugar does
56. 2:38not conduct electric current in a way
57. 2:41that our device could detect.
58. 2:43Experiment three. Sugar solution. And
59. 2:46now let's dissolve the sugar in water.
60. 2:48It would seem that after dissolving,
61. 2:50the properties of the substance could
62. 2:52change. Let's check this. The light
63. 3:00bulb still does not light up. Why?
64. 3:07During dissolution, sugar breaks down
65. 3:10into individual molecules that are
66. 3:12evenly distributed among the water
67. 3:14molecules. However, these molecules do
68. 3:17not turn into ions. Therefore, the
69. 3:19sugar solution practically does not
70. 3:21conduct electric current. Dissolving
71. 3:23substances in water is not always
72. 3:25accompanied by the formation of ions.
73. 3:28Experiment four. Citric acid. The next
74. 3:32object of our research is citric acid.
75. 3:35First, let's check the dry substance.
76. 3:39As we can see, the light bulb does not
77. 3:41light up. This is an expected result,
78. 3:46as there are no free mobile ions in dry
79. 3:48citric acid capable of ensuring a
80. 3:50noticeable flow of current through the
81. 3:53sample. But what will happen if we
82. 3:56dissolve citric acid in water?
83. 3:58Experiment five. Citric acid solution.
84. 4:02We prepare an aqueous solution of
85. 4:04citric acid and immerse the electrodes.
86. 4:12Note that the light bulb still does not
87. 4:15light up. Can we conclude that a citric
88. 4:18acid solution does not conduct electric
89. 4:20current at all? No, we cannot. In an
90. 4:25aqueous solution, only a small portion
91. 4:27of its molecules form ions, so the
92. 4:29solution conducts electricity, but its
93. 4:31conductivity may not be sufficient for
94. 4:33our device's light bulb to glow. So, as
95. 4:37we can see, the result depends on both
96. 4:39the properties of the solution and the
97. 4:41sensitivity of the device. Experiment
98. 4:44six. Crystalline alkali. Moving on to
99. 4:47examine alkali. Unlike sugar, alkali is
100. 4:50an ionic substance. Its crystal lattice
101. 4:53contains positively and negatively
102. 4:55charged ions. However, in the solid
103. 4:59state, these ions are fixed in the
104. 5:01crystal lattice nodes and cannot move
105. 5:03freely. We check the electrical
106. 5:06conductivity of the sample and see that
107. 5:12the bulb does not light up. Therefore,
108. 5:14the mere presence of ions in a
109. 5:16substance does not guarantee electrical
110. 5:18conductivity. It is important that
111. 5:20these ions are able to move. Experiment
112. 5:23seven. Alkali solution. Now let's
113. 5:26examine an aqueous solution of alkali.
114. 5:28After dissolving in water, the ions
115. 5:30become mobile. They can move under the
116. 5:33influence of an electric field and
117. 5:36carry an electric charge. As we can see
118. 5:46, the bulb lights up. This indicates
119. 5:48that the solution conducts electric
120. 5:51current well. It is the mobility of the
121. 5:53ions that explains this difference.
122. 5:55Experiment eight. Copper sulfate. The
123. 5:59next substance is copper sulfate or
124. 6:01copper (II) sulfate pentahydrate. It is
125. 6:04easily recognized by the characteristic
126. 6:06blue color of its crystals. Let's check
127. 6:08the electrical conductivity of the dry
128. 6:10sample. The bulb does not light up. As
129. 6:14in the case of solid alkali, the ions
130. 6:17are contained in a crystal lattice but
131. 6:19do not have the ability to move freely.
132. 6:22Therefore, solid copper sulfate does
133. 6:25not ensure a noticeable passage of
134. 6:27electric current in our experiment.
135. 6:31Experiment nine. Copper (II) sulfate
136. 6:34solution. Now we dissolve copper
137. 6:37sulfate in water. A blue solution is
138. 6:40formed. Let's check its electrical
139. 6:43conductivity. The bulb lights up.
140. 6:47During dissolution in water, mobile
141. 6:50ions are formed. copper and sulfate
142. 6:54ions. They provide the transfer of
143. 6:57electric charge. Solid copper sulfate
144. 7:00did not cause the bulb to glow, but its
145. 7:02aqueous solution conducts electric
146. 7:04current. Thus, electrical conductivity
147. 7:08depends on whether the charged
148. 7:10particles can move freely. Experiment
149. 7:1310. Hydrochloric acid solution.
150. 7:17Hydrochloric acid is an aqueous
151. 7:18solution of hydrogen chloride. Hydrogen
152. 7:22chloride forms hydrogen ions and
153. 7:24chloride anions almost completely. The
154. 7:27bulb lights up. This means that the
155. 7:30solution conducts electric current well
156. 7:32. Hydrochloric acid belongs to strong
157. 7:35electrolytes because it ionizes almost
158. 7:37completely in water. Compare this
159. 7:40experiment with the experiment
160. 7:41involving citric acid solution. In both
161. 7:44cases, we are dealing with acids, but
162. 7:46the results differ. In the hydrochloric
163. 7:50acid solution, the bulb lights up, but
164. 7:52in the citric acid solution, it does
165. 7:53not. Next, write the conclusions for
166. 7:57the work. I invite you to answer the
167. 8:00following questions: why was the bulb
168. 8:02not glowing in the experiments with dry
169. 8:05substances? What does the electrical
170. 8:08conductivity of solutions depend on?
171. 8:10Why can't one claim that a solution
172. 8:12does not conduct current at all just
173. 8:15because the bulb did not light up?
174. 8:19Reflection. In conclusion, I suggest
175. 8:22you reflect on these questions. What
176. 8:24new things did you learn during the
177. 8:27research? Which result surprised you
178. 8:29the most? Thank you for your work. I
179. 8:33hope today's experiment helped you see
180. 8:36that chemistry is not just formulas and
181. 8:38equations, but also a chance to explore
182. 8:41the properties of substances and
183. 8:43explain the phenomena around us. Until
184. 8:47next time, and happy researching.