Photo AI
Ethene gas can be prepared from ethanol in a school laboratory - Leaving Cert Chemistry - Question 2 - 2012
Question 2
Ethene gas can be prepared from ethanol in a school laboratory. (a) Draw a labelled diagram showing the arrangement of apparatus and the reagents used in the prepar... show full transcript
Worked Solution & Example Answer:Ethene gas can be prepared from ethanol in a school laboratory - Leaving Cert Chemistry - Question 2 - 2012
Step 1
Draw a labelled diagram showing the arrangement of apparatus and the reagents used in the preparation and collection of the ethene.
Answer
To prepare ethene gas from ethanol, the apparatus should include:
- A suitable reaction container, such as a test tube, containing ethanol.
- Glass wool to hold the ethanol while it is heated.
- Aluminium oxide (Al₂O₃) as a catalyst.
- A heating device to heat the mixture.
- A delivery tube connecting the reaction container to a water trough for collection.
- Underneath the delivery tube, a container to collect the ethene gas, such as an inverted measuring cylinder or graduated cylinder submerged in water.
Step 2
Step 3
Step 4
How could a 'suck-back' be avoided?
Answer
To avoid a 'suck-back', a safety device such as a one-way tap (or a suitable stopper) should be fitted to the delivery tube to prevent backflow of the water. Additionally, maintaining constant heating and ensuring the test tube is not removed from the water can help mitigate this risk.
Step 5
Describe how you could test the gas produced for unsaturation.
Answer
To test the gas produced for unsaturation, bubble the ethene gas through a solution of bromine water. The solution will change color from reddish-brown to colorless if unsaturation is present, indicating the ethene has reacted with the bromine.
Step 6
Step 7
Assuming this percentage yield, what is the maximum number of 75 cm³ test tubes of ethene gas that could be collected?
Answer
First, calculate the moles of ethanol used:
- Volume of ethanol = 2.4 cm³ (which equals 0.0024 L)
- Density = 0.8 g cm³ ➔ Mass = Volume × Density = 2.4 × 0.8 = 1.92 g
- Molar mass of ethanol (C₂H₅OH) = 46.08 g/mol
- Moles of ethanol = Mass / Molar mass = 1.92 g / 46.08 g/mol = 0.0417 mol
Given the reaction shows a 1:1 ratio;
- Moles of ethene produced = 0.0417 mol × 0.60 (yield) = 0.02502 mol
Using ideal gas equation (at RTP, 1 mol ≈ 24 dm³):
- Volume of ethene at RTP = 0.02502 mol × 24 dm³/mol = 0.60048 dm³ = 600.48 cm³
Calculate the maximum number of test tubes:
- Volume of one test tube = 75 cm³.
- Maximum number of test tubes = Total volume of ethene / Volume of one test tube = 600.48 cm³ / 75 cm³ = 8.01.
Thus, you can collect a maximum of 8 test tubes of ethene gas at room temperature and pressure.