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a) The diagram shows a sequence of steps in the removal of grease from a surface - HSC - SSCE Chemistry - Question 32 - 2013 - Paper 1
Question 32
a) The diagram shows a sequence of steps in the removal of grease from a surface. Explain the process shown in these steps. b) Hydrogen iodide is a colourless gas t... show full transcript
Worked Solution & Example Answer:a) The diagram shows a sequence of steps in the removal of grease from a surface - HSC - SSCE Chemistry - Question 32 - 2013 - Paper 1
Step 1
Explain the process shown in these steps.
Answer
The steps illustrate the mechanism by which grease is removed from a surface using a surfactant.
- Step 1: Grease particles adhere to the surface due to strong intermolecular forces.
- Step 2: The surfactant, which has both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions, is introduced. The hydrophobic part of the surfactant interacts with the grease, while the hydrophilic part interacts with water, forming an emulsion.
- Step 3: As the surfactant molecules surround the grease, they reduce its surface tension, allowing it to be easily washed away with water.
Step 2
Calculate the equilibrium constant for this reaction.
Answer
Given the reaction:
At equilibrium,
- Moles of HI = Initial moles - Used moles
- Moles of HI = 0.60 - 0.25 = 0.35 moles
- Volume = 1.0 L
Concentration of each species at equilibrium:
- [HI] = 0.35 M
- [H2] = 0.25 M
- [I2] = 0.25 M
The equilibrium constant expression is:
Substituting in the equilibrium concentrations:
Step 3
Explain the change in the appearance of its contents.
Answer
Since the reaction is endothermic, cooling the reaction vessel will shift the equilibrium position to the left, favoring the formation of the reactants.
As a result, the concentration of purple iodine gas I2 will decrease, leading to a lighter shade of purple in the container's contents.