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  • In this lesson, we will learn how to test for the presence of hydrogen, oxygen, carbon

  • dioxide, ammonia, and chlorine.

  • We test for gases in the laboratory because it is nearly impossible to determine the identity

  • of a gas just by its appearance.

  • As an example, hydrogen, oxygen, and carbon dioxide are all colourless and odourless.

  • How would we be able to determine which is which?

  • To test for hydrogen, place a lit splint at the mouth of the reaction vessel.

  • You should hear a very distinctivesqueaky pop�, which confirms its presence.

  • This is due to the combustion reaction of hydrogen in the presence of oxygen, creating

  • water as the only product.

  • To test for oxygen, place a glowing splint at the mouth of the reaction vessel.

  • Keep in mind that the splint should beglowing�, not lit.

  • A glowing splint relights in the presence of oxygen.

  • Why does hydrogen burn with a �squeakypop?

  • Why does oxygen relight the glowing splint?

  • Hint: recall some properties of hydrogen and oxygen.

  • Please pause the lesson to think about this and resume once you are done.

  • Hydrogen is highly flammable and the pop sound that you hear is actually a mini-explosion.

  • The glowing splint relights in the presence of oxygen as there is a higher concentration

  • of oxygen in the reaction vessel than compared with air, which is only 21% oxygen.

  • Carbon dioxide will extinguish a lit splint, but the same occurs in the presence of ammonia.

  • A more accurate test is to bubble carbon dioxide though limewater, which is an aqueous solution

  • of calcium hydroxide, also known as slaked lime.

  • Limewater turns milky in the presence of carbon dioxide due to the formation of calcium carbonate.

  • Ammonia extinguishes a lit split, and turns damp red litmus paper blue.

  • In the presence of concentrated hydrochloric acid, a white smoke will form.

  • This is ammonium chloride, and confirms the presence of ammonia.

  • Chlorine turns damp blue litmus paper red and eventually bleaches it to white.

  • In conclusion, hydrogen burns with a �squeakypop, oxygen relights a glowing splint, and

  • carbon dioxide turns limewater milky.

  • Ammonia turns damp red litmus paper blue and forms a white smoke of ammonium chloride in

  • the presence of concentrated hydrochloric acid.

  • Chlorine turns damp blue litmus paper red and continues to bleach it white.

In this lesson, we will learn how to test for the presence of hydrogen, oxygen, carbon

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氫氣、氧氣、二氧化碳、氨氣和氯氣的測試|化學之旅 (Testing for Hydrogen, Oxygen, Carbon Dioxide, Ammonia and Chlorine | The Chemistry Journey)

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    Yrchinese 發佈於 2021 年 01 月 14 日
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