'to test for gases, collect hydrogen by inverting a test tube over water. a pop sound with a lit splint indicates its presence.' -- i dontunderstand, why is that chemical reaction happening? how is there a pop sound?
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When testing for hydrogen gas, we collect it by inverting a test tube over water. A lit splint creates a distinctive pop sound if hydrogen is present. But why does this pop sound occur? The answer lies in a rapid chemical reaction between hydrogen and oxygen in the air.
The pop sound is caused by a combustion reaction between hydrogen gas and oxygen from the air. The chemical equation is: two H two plus O two yields two H two O plus energy. This reaction is highly exothermic, meaning it releases a large amount of energy very quickly.
Here's how the pop sound forms step by step. First, the lit splint provides activation energy to start the reaction. Second, rapid energy release heats the gases, causing sudden expansion. Third, this sudden gas expansion creates a pressure wave. Fourth, the pressure wave travels through the air as sound - the pop!
The hydrogen test is highly specific because hydrogen is the only common gas that produces this distinctive pop sound when ignited. Other gases behave differently. Oxygen supports combustion but doesn't burn itself, so no pop. Carbon dioxide extinguishes flames with no reaction. Methane burns with a steady flame but no sharp pop sound. This makes the pop test a reliable and safe method for identifying hydrogen gas in the laboratory.