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12. (a) The concentration of sodium hypochlorite in swimming pool water can be determined by redox titration - Scottish Highers Chemistry - Question 12 - 2015
Question 12
12. (a) The concentration of sodium hypochlorite in swimming pool water can be determined by redox titration. Step 1 A 100-0 cm³ sample from the swimming pool is fi... show full transcript
Worked Solution & Example Answer:12. (a) The concentration of sodium hypochlorite in swimming pool water can be determined by redox titration - Scottish Highers Chemistry - Question 12 - 2015
Step 1
Describe in detail how a burette should be prepared and set up, ready to begin the titration.
Answer
To prepare and set up the burette:
- Rinse the Burette: Start by rinsing the burette with the sodium thiosulfate solution to avoid contamination.
- Fill the Burette: Fill the burette with the thiosulfate solution, making sure to remove any air bubbles that may be trapped.
- Ensure Proper Setup: Ensure the burette is positioned vertically and the reading is taken from the bottom of the meniscus to ensure accuracy.
Step 2
Calculate the concentration, in mol⁻¹, of sodium hypochlorite in the swimming pool water, if an average volume of 12·4 cm³ of sodium thiosulfate was required.
Answer
To calculate the concentration:
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Convert Volume to Litres: The average volume of sodium thiosulfate used is 12.4 cm³, which is equal to 0.0124 L.
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Calculate Moles of Thiosulfate: Using the concentration of sodium thiosulfate (0.00100 mol·L⁻¹), the moles of thiosulfate used can be calculated:
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Use Stoichiometric Relationships: According to the reaction:
ightarrow I₂ + ext{NaCl} + H₂O$$
1 mole of sodium hypochlorite reacts with 2 moles of thiosulfate, giving:
ext{Moles of NaOCl} = rac{0.0000124}{2} = 0.0000062 ext{ moles}
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Calculate Concentration of NaOCl: The volume of the NaOCl sample was 0.1 L, thus:
ext{Concentration of NaOCl} = rac{0.0000062 ext{ moles}}{0.1 ext{ L}} = 0.000062 ext{ mol·L⁻¹}
Step 3
Explain the difference in polarities of ammonia and trichloramine molecules.
Answer
Ammonia (NH₃) is a polar molecule because of the electronegativity difference between nitrogen and hydrogen, resulting in a net dipole moment. On the other hand, trichloramine (NCl₃) has non-polar characteristics because chlorine's electronegativity is similar to that of nitrogen, causing the dipoles to cancel each other out. This results in trichloramine not having a net dipole moment, making it non-polar.
Step 4
State what is meant by the term free radical.
Answer
A free radical is defined as an atom or a molecule that contains an unpaired electron in its outer shell, making it highly reactive. Free radicals can initiate chain reactions because they seek to pair their unpaired electron by interacting with other molecules.
Step 5