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Ethanoic acid, ethanol and ethanol are three colourless organic substances, all liquids at 18 °C - Leaving Cert Chemistry - Question 2 - 2019
Question 2
Ethanoic acid, ethanol and ethanol are three colourless organic substances, all liquids at 18 °C. A student was provided with small, pure samples of each of these su... show full transcript
Worked Solution & Example Answer:Ethanoic acid, ethanol and ethanol are three colourless organic substances, all liquids at 18 °C - Leaving Cert Chemistry - Question 2 - 2019
Step 1
What was observed?
Answer
When magnesium ribbon is placed in ethanoic acid, a vigorous reaction occurs. This is characterized by the following observations:
- Bubbling and fizzing due to the release of hydrogen gas.
- A solid (magnesium) dissolves as it reacts with the acid.
- A white precipitate may form from the reaction.
Step 2
Step 3
Describe a chemical test to show that ethanol can be very easily oxidised.
Answer
To test for the oxidation of ethanol, you can use a mild oxidizing agent such as Tollen's reagent (AgNO₃ in aqueous ammonium hydroxide). When ethanol is oxidized, it will produce an aldehyde. The presence of the aldehyde can be detected by observing the formation of a silver mirror on the inner surface of the test tube.
Step 4
Draw a diagram of an arrangement of apparatus for the preparation and collection of ethene.
Answer
- Draw a horizontal test tube inclined downward with a delivery tube leading to a water collection jar.
- Indicate that the test tube is heated at one end and has a catalyst, such as alumina ( ( Al_2O_3 )), placed in it.
- Label all parts, including the heat source, ethene collection apparatus, and the catalyst.
Step 5
Identify the catalyst and describe its role in the beginning of the preparation.
Answer
The catalyst used is aluminum oxide (( Al_2O_3 )). Its role is to facilitate the dehydration of ethanol into ethene by providing a surface for the reaction to occur, allowing the reaction to proceed at a lower temperature and increasing the rate of production of ethene.
Step 6
Explain why there is a risk of glassware shattering, due to rapid cooling, associated with this preparation.
Answer
The risk of glassware shattering arises from rapid temperature changes. When hot glassware comes into contact with cooler substances, it can lead to uneven expansion and contraction, creating stress on the glass. This can result in cracks or even breakage, making it important to manage cooling rates carefully.
Step 7
Calculate the volume of ethene gas produced in 26% yield when measured at room temperature and pressure.
Answer
Starting with 2.9 cm³ of ethanol (density 0.8 g cm³), we first calculate the mass:
Mass = volume × density = 2.9 cm³ × 0.8 g/cm³ = 2.32 g.
Using the molar mass of ethanol (C₂H₅OH), which is approximately 46 g/mol, we find the number of moles:
( ext{moles of ethanol} = \frac{2.32 g}{46 g/mol} = 0.0504 \text{ moles} ).
From the balanced equation, each mole of ethanol produces one mole of ethene. Therefore, at 26% yield:
( ext{ethene produced} = 0.0504 imes 0.26 = 0.0131 \text{ moles} ).
At room temperature and pressure, 1 mole of gas occupies 24.0 liters:
( ext{Volume of ethene} = 0.0131 moles \times 24.0 L/mol \approx 0.315 L. )