Collecting gas over water with a eudiometer

In summary, when using a eudiometer in a lab to collect gas over water, the final volume of water displaced is equal to the sum of the water displaced in the first and second eudiometers. The pressure can be calculated by adding the heights of both eudiometer tubes. In the given example, the total volume of gas produced is 73mL and the final pressure is 770mmH2O. Ignoring the first portion of gas collected would result in a different final volume. The reasoning behind this is that the first portion of gas collected is also a part of the overall gas produced and should not be ignored.
  • #1
elements
29
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Homework Statement


When, using a eudiometer in a lab to collect gas over water, if you have to switch eudiometers is the final volume of water displaced equal to the water displaced in the first tube + the water displaced in the second, and would the pressure be calculated through the total height displaced?

i.e.

Collecting butene gas from a reaction of BuBr and KOH in a 50mL eudiometer tube. The first tube all of the 50mL of H2O is displaced and the second tube 23mL is displaced.

Homework Equations


Total Volume = Volume displaced in first tube + Volume displaced in second
Pressure = Pressure of both heights combined

The Attempt at a Solution


Total Volume of gas produced = 50mL + 23mL=73mL of gas produced
Pressure = 50cm+(50-23cm)=770mmH2O
 
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  • #2
elements said:
is the final volume of water displaced equal to the water displaced in the first tube + the water displaced in the second

And what is the alternative?
 
  • #3
just the final volume of water displaced in the second eudiometer tube
 
  • #4
So, what its the reasoning behind ignoring the first portion of gas collected?

Imagine using twice larger tube - should you get the same result, or a different one from the same experiment? Would you get the same result if you ignore the volume collected in the first tube?
 

FAQ: Collecting gas over water with a eudiometer

1. How does a eudiometer collect gas over water?

A eudiometer is a laboratory apparatus used to collect gas over water. It consists of a graduated glass tube with one end closed and the other end open. The open end is submerged in a beaker or trough filled with water. As gas is produced or introduced into the eudiometer, it displaces the water, causing it to rise up the tube.

2. Why is collecting gas over water important in scientific experiments?

Collecting gas over water allows for the measurement of the volume of gas produced or introduced. This is important in many scientific experiments, as the volume of gas can be used to calculate important variables such as molar mass and gas laws.

3. What is the purpose of the inverted water displacement method in collecting gas over water?

The inverted water displacement method is used to ensure that the gas collected in the eudiometer is pure. This is because the water acts as a barrier, preventing any impurities from entering the gas sample. This method also allows for the measurement of the volume of gas collected.

4. How do you calculate the volume of gas collected over water using a eudiometer?

To calculate the volume of gas collected, subtract the initial volume of water in the eudiometer from the final volume after the gas has been collected. The difference in volume represents the volume of gas collected.

5. Are there any limitations to using a eudiometer to collect gas over water?

One limitation of using a eudiometer is that it can only collect gases that are soluble in water. This means that some gases may not be able to be accurately measured using this method. Additionally, the water temperature and pressure can also affect the volume of gas collected, so these factors should be taken into consideration during experimentation.

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