Why Should a Thistle Tube Be Kept Below the Acid Level in Acid-Metal Reactions?

[apchemstudent]

This might seem like a chemistry question, but the principle behind it is mainly physics.

How does keeping the thistle tube below the acid level prevent gas from seeping through it in a acid and metal reaction? In case you are wondering the thistle tube is the tube with a bulb-like opening at the top in the attachment. In the diagram, the thistle tube is above the acid level, but that's not the point, since it's just to show you what it looks like. Please explain this. Thanks.

 

[Andrew Mason]

This might seem like a chemistry question, but the principle behind it is mainly physics.

How does keeping the thistle tube below the acid level prevent gas from seeping through it in a acid and metal reaction? In case you are wondering the thistle tube is the tube with a bulb-like opening at the top in the attachment. In the diagram, the thistle tube is above the acid level, but that's not the point, since it's just to show you what it looks like. Please explain this. Thanks.

Where is the metal?

The metal reacting with the acid will create gas bubbles which will rise vertically through the acid to the surface and add to the pressure in the stoppered bottle. If the thistle tube end is below the surface of the acid and to the side of the metal, no gas will enter the tube. If it is above the metal or if the metal is a powder distributed throughtout the acid, some portion of the gas being emitted would enter the tube. I would think that this proportion would be: area of tube opening/area of metal if the metal is a surface below the tube. If the metal is mixed with the acid, the proportion would be: (volume of acid below tube end)/(volume of total liquid/metal) .

So if you make the diameter small compared to the surface of the metal, and, in the case of powdered metal in suspension in the acid, if you lower the end to a point near the bottom, not much gas will get through.

AM

 

[wais]

The principle behind keeping the thistle tube below the acid level in an acid and metal reaction is based on the concept of pressure. When the thistle tube is below the acid level, the gas produced in the reaction is trapped inside the tube, creating a higher pressure inside the tube compared to the surrounding atmosphere. This higher pressure prevents any gas from seeping through the tube and escaping into the atmosphere.

On the other hand, if the thistle tube was above the acid level, the gas produced in the reaction would be able to escape into the atmosphere, equalizing the pressure inside and outside the tube. This would result in a lower pressure inside the tube, allowing gas to seep through and escape.

Furthermore, the thistle tube also acts as a barrier between the acid and the metal, preventing direct contact between the two. This is important because the reaction between the acid and metal can become more vigorous and produce larger amounts of gas, which could potentially cause the reaction to become uncontrollable or even dangerous. The thistle tube helps to control the release of gas and maintain a safe environment.

In summary, keeping the thistle tube below the acid level in an acid and metal reaction is crucial in maintaining a controlled and safe environment. It prevents gas from seeping through and escaping, and also acts as a barrier between the acid and metal to control the reaction. This principle is based on the physics of pressure and is an important concept to understand in chemistry experiments.