A student prepared ethene and ethyne gases and compared their properties - Leaving Cert Chemistry - Question 2 - 2017

The first few test-tubes of gas were discarded because they likely contained moisture and impurities from the reaction. Freshly produced ethyne gas is the desired product, free from water vapor or byproducts.

The diagram should include a reaction flask with ethene being collected over water. The setup includes ethanoic acid as a reactant, a delivery tube, and a water bath. Ensure to label each component accurately.

1. Use protective eyewear to prevent eye injury from splashes or reactions.
2. Work in a well-ventilated area to avoid inhalation of any gases produced during the reaction.

During the combustion test, ethene burns with a blue flame, producing less soot and showing a clean burning. Ethyne, on the other hand, burns with a luminous yellow flame, indicating the production of more soot due to incomplete combustion.

The balanced equation for the complete combustion of ethene (C₂H₄) is:

$C_2H_4 + 3O_2 → 2CO_2 + 2H_2O$

A common reagent used to test for unsaturation in gases is bromine water (Br₂ in water), which changes color when it reacts with unsaturated hydrocarbons.

Given that 0.05 moles of calcium carbide (CaC₂) was used and considering the molar ratio from the equation, the maximum number of ethyne (C₂H₂) molecules produced can be calculated as follows:

1. Determine moles of CaC₂: 0.05 moles
2. From the reaction, 1 mole of CaC₂ produces 1 mole of C₂H₂.
3. Thus, moles of C₂H₂ produced = 0.05 moles.
4. To find the number of molecules, use Avogadro's number (6.022 x 10²³):

$0.05 ext{ moles} imes 6.022 imes 10^{23} ext{ molecules/mole} = 3.01 imes 10^{22} ext{ molecules}$