We test for gases in the laboratory because it is nearly impossible to determine the identity of a gas just by its appearance.

我們之所以會在實驗室檢測氣體存在，是因為單憑外表幾乎不可能判定氣體種類。

As an example, hydrogen, oxygen, and carbon dioxide are all colorless and odorless.

舉例而言，氫氣、氧氣以及二氧化碳都無色無味。

How would we be able to determine which is which?

我們要怎麼能夠判別何者為何呢？

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

要檢測氫氣存在與否，在反應器口放置點燃的木條。

You should hear a very distinctive, squeaky "pop", which confirms its presence.

你應該會聽到很清楚、吱吱作響的「碰」一聲，這足以確認其存在。

This is due to the combustion reaction of hydrogen in the presence of oxygen, creating water as the only product.

這是因為氫氣在氧氣存在狀態下的燃燒反應，並生成單一產物，也就是水。

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

要檢測氧氣存在，在反應器口放置具火光的木條。

Keep in mind that the splint should be glowing, not lit.

注意木條應該是火光閃爍，而不是燃燒狀態。

A glowing splint relights in the presence of oxygen.

火光閃爍的木條會因為氧氣存在重新燃起。

Why does hydrogen burn with a squeaky "pop"?

那氫氣燃燒時為什麼會有吱吱響的「砰」聲呢？

Why does oxygen relight the glowing splint?

氧氣為什麼會讓閃火光的木條重新燃起火焰？

Hint: recall some properties of hydrogen and oxygen.

提示：回想氫氣以及氧氣的一些特性。

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

請暫停課程稍作思考，並在完成後繼續播放。

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

氫氣高度可燃，所以你聽到的「碰」聲其實是一個微型爆炸。

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.

閃火光木條在有氧氣存在時重燃是因為反應器中跟空氣中相比之下，有較高度濃縮的氧氣，空氣中只有 21% 氧氣。

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

二氧化碳會將點燃的木條熄滅，但同樣的現象也會發生在有氨氣存在時。

A more accurate test is to bubble carbon dioxide through limewater, which is an aqueous solution of calcium hydroxide, also known as slaked lime.

較準確的測試方式是透過鹼水煮沸二氧化碳，鹼水是氫氧化鈣的水溶液，又稱石灰水。

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

鹼水會在有二氧化碳存在的時候變得混濁，這是歸因於碳酸钙的生成。

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

氨氣會將點燃的木條熄滅，並會將浸濕的石蕊試紙由紅轉藍。

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

若有高度濃縮的鹽酸存在，將會有白煙生成。

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

這就是氯化銨，證實了氨氣的存在。

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

氯氣會將浸濕的石蕊試紙由藍轉紅，最終漂白。

In conclusion, hydrogen burns with a squeaky "pop", oxygen relights a glowing splint, and carbon dioxide turns limewater milky.

結論如下：氫氣燃燒時會發出吱吱響的「砰」聲、氧氣會將發火光的木條重新點燃，而二氧化碳則會將鹼水變混濁。

Ammonia turns damp red litmus paper blue and forms a white smoke of ammonium chloride in the presence of concentrated hydrochloric acid.

氨氣會將浸濕的石蕊試紙由紅轉藍，且在有高度濃縮鹽酸存在時，生成稱為氯化銨的白煙。

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

氯氣會將浸濕的石蕊試紙由藍轉紅，進而將其漂白。