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A student is given a bucket of seawater - Leaving Cert Chemistry - Question a - 2008
Question a
A student is given a bucket of seawater. (i) Describe how the student could determine by filtration the total suspended solids (expressed as ppm) in the water. (ii... show full transcript
Worked Solution & Example Answer:A student is given a bucket of seawater - Leaving Cert Chemistry - Question a - 2008
Step 1
Describe how the student could determine by filtration the total suspended solids (expressed as ppm) in the water.
Answer
To determine the total suspended solids in the seawater, the student should follow these steps:
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Preparation of Equipment: Start by preparing a clean, dry filter paper. Weigh the filter paper accurately and record this initial weight.
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Filtration Process: Pour a known volume of seawater through the weighed filter paper. Ensure that the filtration process allows for the suspended solids to be trapped on the filter paper.
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Drying the Filter Paper: After the filtration, place the filter paper in an oven to dry completely. This ensures that all moisture is removed, which is crucial for accurate weighing.
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Weighing the Filter Paper: Once dried, allow the filter paper to cool in a desiccator to prevent moisture absorption. Then, reweigh the filter paper with the suspended solids.
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Calculating Suspended Solids: Subtract the initial weight of the dry filter paper from the final weight to find the mass of the suspended solids. Convert the mass obtained into parts per million (ppm) by applying the formula:
ext{ppm} = rac{ ext{mass of solids (mg)}}{ ext{volume of water (L)}} \times 1000
This calculation provides the total suspended solids in ppm.
Step 2
How could the student determine the total dissolved solids (expressed as ppm) in a sample of the filtered seawater?
Answer
To determine the total dissolved solids in the filtered seawater, the student should do the following:
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Evaporating the Water: Take a known volume of the filtered seawater and transfer it to a weighed container, such as a clean dish.
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Evaporation Process: Heat the container gently to evaporate the water completely. Be careful to avoid overheating, which may alter some dissolved solids.
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Cooling and Weighing: Once all the water has evaporated, allow the container to cool. Weigh the container again to find the new weight, including the dissolved solids.
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Calculating Total Dissolved Solids: Subtract the initial weight of the empty container from the final weight to find the mass of the dissolved solids. Again, to express this result in ppm, use the following formula:
ext{ppm} = rac{ ext{mass of solids (mg)}}{ ext{volume of water (L)}} \times 1000
This calculation allows the student to quantify the total dissolved solids in ppm.
Step 3
Describe a test to confirm the presence of the chloride ion in aqueous solution.
Answer
To confirm the presence of chloride ions in an aqueous solution, the student can perform the following test:
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Adding Reagents: Take a small sample of the suspected chloride solution in a test tube and add a few drops of silver nitrate solution (AgNO₃).
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Observing the Reaction: If chloride ions are present, a white precipitate of silver chloride (AgCl) will form immediately. This precipitate indicates the presence of chloride ions in the solution.
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Solubility in Ammonia: To further confirm the presence, the white precipitate can be treated with dilute ammonia solution. Silver chloride will dissolve in ammonia, producing a colorless solution, which serves as an additional confirmation that chloride ions were present initially.