In an experiment to measure the heat of reaction (ΔH) for the neutralisation of hydrochloric acid and sodium hydroxide solution, 100 cm³ of 1 M HCl solution was added to 100 cm³ of 1 M NaOH solution in a polystyrene container with a cardboard lid - Leaving Cert Chemistry - Question 3 - 2012
Question 3
In an experiment to measure the heat of reaction (ΔH) for the neutralisation of hydrochloric acid and sodium hydroxide solution, 100 cm³ of 1 M HCl solution was adde... show full transcript
Worked Solution & Example Answer:In an experiment to measure the heat of reaction (ΔH) for the neutralisation of hydrochloric acid and sodium hydroxide solution, 100 cm³ of 1 M HCl solution was added to 100 cm³ of 1 M NaOH solution in a polystyrene container with a cardboard lid - Leaving Cert Chemistry - Question 3 - 2012
Step 1
Was heat released or absorbed when the HCl and NaOH solutions reacted?
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Answer
Heat was released during the reaction.
This is because the temperature of the container increased, indicating an exothermic reaction. The ΔH value being negative supports the conclusion that heat is released.
Step 2
What features of the apparatus described help prevent heat loss to the surroundings? Why should the mixture be stirred before taking temperature readings?
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Answer
The apparatus includes insulation made of plastic (polystyrene) and a cardboard lid, which help to retain heat.
Stirring the mixture ensures even distribution of temperature throughout the solution, preventing localized cold spots and allowing for a more accurate temperature reading.
Step 3
Name a piece of apparatus that could have been used to measure accurately 100 cm³ of the NaOH solution.
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A graduated cylinder or volumetric flask could be used to measure 100 cm³ accurately.
Step 4
What chemical hazard is indicated by this symbol?
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Answer
The symbol indicates that the NaOH solution is corrosive.
Step 5
Describe the precautions that should be taken to ensure safety.
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Precautions include wearing gloves and eye protection to prevent skin and eye contact with the corrosive solution, as well as ensuring that bottles are carried by the neck and not by the body to avoid spills.
Step 6
What temperature rise would you expect to record?
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The expected temperature rise would be approximately 3.4 °C, as only half the acid is neutralised when 0.5 M NaOH is used.
Step 7
Justify your answer.
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This is because using a lower concentration of NaOH reduces the amount of base available to react with the acid, leading to a smaller temperature change compared to the reaction with 1 M NaOH.
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