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A student was given a bucket of sea water for analysis - Leaving Cert Chemistry - Question 3 - 2006
Question 3
A student was given a bucket of sea water for analysis. The student was asked to find out the concentrations of suspended and dissolved solids in the sea water. The ... show full transcript
Worked Solution & Example Answer:A student was given a bucket of sea water for analysis - Leaving Cert Chemistry - Question 3 - 2006
Step 1
Why did the student wash the filter paper with distilled water after filtering the sea water?
Answer
The student washed the filter paper with distilled water to remove any dissolved solids that may remain on the filter paper after the filtration process. This ensures that only the suspended solids are left on the paper, allowing for an accurate measurement of the mass. Washing with distilled water also helps to transfer any remaining solids into the collected filtrate.
Step 2
Express the concentration of suspended solids in p.p.m.
Answer
To find the concentration of suspended solids in p.p.m., use the formula:
ext{Concentration} = rac{ ext{Mass of solids (g)}}{ ext{Volume of solution (L)}} imes 1000 \ = rac{0.44 ext{ g}}{0.5 ext{ L}} imes 1000 = 880 ext{ p.p.m.}Step 3
Describe how the student could have measured the concentration of dissolved solids in the sea water.
Answer
The student could have measured the concentration of dissolved solids by weighing a beaker, adding a known volume of sea water, and then evaporating the water completely. After evaporation, the student would weigh the beaker again to find the increase in mass. By calculating the difference in mass, the concentration of dissolved solids can be determined based on the initial volume of the sea water used.
Step 4
Describe how the student could have carried out a flame test to show that a sodium salt was present in the dissolved solids collected. What flame colour would indicate the presence of sodium ions?
Answer
To conduct a flame test, the student should take a sample of the collected solids and prepare it into a paste or solution. Using a clean, dry metal probe, such as a nichrome wire, the student would then dip it into the sample and place it in a Bunsen burner flame. The flame should turn a bright yellow/orange if sodium ions are present, confirming the presence of sodium salts.
Step 5
How could the student have tested the sea water to show that chloride ions were present?
Answer
To test for the presence of chloride ions, the student could add silver nitrate solution (AgNO₃) to a sample of the sea water. If chloride ions are present, a white (or pale) precipitate of silver chloride (AgCl) will form, indicating the presence of chloride ions in the water.