Electrolysis of Water: How Rheostat Affects Bubbles Produced

In summary, when the resistance of a rheostat is increased, the number of bubbles produced per second decreases. This is due to the decrease in current.
  • #1
chanller
25
0
While doing electrolysis of water, I have put a rheostat and a battery in series with the apparatus. I found that when I increase the resistance of the rheostat, the number of bubbles produced per second decreases. How can you explain that?
 
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  • #2
Before we can respond, we need to see what you think. Do you have any idea what other electrical quantities are affected by changing the resistance in a constant-voltage circuit? And the bubbles - what physical quantity do they relate to?
 
  • #3
If the power withdrawn from a battery depends on the resistance of the circuit, then i guess current changes if P=IV. But, how can you keep the voltage from a battery constant while varying power withdrawn?
 
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  • #4
Yes, that's correct, though it actually follows more directly from Ohm's Law, V=IR. So, does the current increase or decrease?
 
  • #5
I believe current for the electrolysis decreases if the voltage is constant and if current = electrons and electrons= gas bubbles, current decreases. Is it that when i increase resistance of the rheostat, power through it increases and that through the electrolysis decreases? This would explain why gas flow decreases but then it would mean power from the battery is constant! But, how can you keep the voltage from a battery constant while varying power withdrawn?
 
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  • #6
There is no need to worry about power here. A bettery is, by definition, a device which produces a constant voltage over a large range of currents. The power dropped (both at the rheostat and at the cell) decreases as you increase the resistance (because the current decreases, while the voltage is constant) but that's not the relevant quantity here. The relevant quantity is the current, which decreases.

As you mentioned, the current is simply the rate at which electrons are transferred between the electrodes. Each pair of electrons arriving at the cathode makes a molecule of hydrogen gas form there. The slower the rate of electrons, the slower will be the rate of hydrogen bubble formation.
 
  • #7
Well, what I did not know is that voltage from a battery is constant; now everything is clear! But can the voltage be changed and if yes, how?
 
  • #8
The battery represents the maximum allowable voltage, and then there is a voltage drop proportional to resisance and current.

Two resistance in series represent a voltage divider.
 
  • #9
I finally had to leaf through my physics book. Well I learned that physics was not just theory which I have to learn by heart! Thanks everyone!
 
  • #10
Talking about electrolysis, what happens to the excess power input when gas production rate remains constant even though power is increased? Droplets of water settled at the top of my gas storage cylinder, does this mean excess power is converted into heat which vaporises water in the electrolyte?
 
  • #11
chanller said:
Talking about electrolysis, what happens to the excess power input when gas production rate remains constant even though power is increased? Droplets of water settled at the top of my gas storage cylinder, does this mean excess power is converted into heat which vaporises water in the electrolyte?
There is heat involved from resistance, and the heat will cause some liquid to evaporate which would condense on a cooler surface.
 
  • #12
If i use 1 molar sulphuric acid at rtp what voltage do you think i should use? 1.5V will be good?

Also, how can i keep the concentration of the acid constant?
 

1. How does a rheostat affect the amount of bubbles produced during the electrolysis of water?

A rheostat is a variable resistor that is used to control the flow of electric current. When a rheostat is used in the electrolysis of water, it can adjust the voltage and current being delivered to the electrodes. This affects the rate at which the water molecules are split into hydrogen and oxygen gas, resulting in more or less bubbles being produced.

2. What is the purpose of using a rheostat in the electrolysis of water?

The purpose of using a rheostat in the electrolysis of water is to control the rate of the electrolysis reaction. This allows for a more controlled and gradual production of hydrogen and oxygen gas, rather than a sudden and potentially dangerous release of gas.

3. Does the type of rheostat used affect the amount of bubbles produced during electrolysis of water?

Yes, the type of rheostat used can affect the amount of bubbles produced during electrolysis of water. Different types of rheostats have different resistance values and can handle different amounts of current. This can impact the voltage and current being delivered to the electrodes, ultimately affecting the rate of the electrolysis reaction and the amount of bubbles produced.

4. How can the amount of bubbles produced during electrolysis of water be measured?

The amount of bubbles produced during electrolysis of water can be measured by collecting the gas in a graduated cylinder or gas collection tube. The volume of gas can then be measured and compared to the expected stoichiometric ratio of hydrogen and oxygen gas produced during electrolysis.

5. Is there an ideal rheostat setting for maximum bubble production during electrolysis of water?

There is no one ideal rheostat setting for maximum bubble production during electrolysis of water. The optimal setting will depend on factors such as the type of electrolysis setup, the concentration of the electrolyte solution, and the type of electrodes being used. It is important to carefully adjust the rheostat and monitor the bubble production in order to achieve the desired result.

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