A student was asked to confirm that a sample of water from the Dead Sea, a lake in Israel, had a very high concentration of dissolved solids including sodium chloride (NaCl) - Leaving Cert Chemistry - Question 3 - 2019
Question 3
A student was asked to confirm that a sample of water from the Dead Sea, a lake in Israel, had a very high concentration of dissolved solids including sodium chlorid... show full transcript
Worked Solution & Example Answer:A student was asked to confirm that a sample of water from the Dead Sea, a lake in Israel, had a very high concentration of dissolved solids including sodium chloride (NaCl) - Leaving Cert Chemistry - Question 3 - 2019
Step 1
Why was the lake water filtered first?
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Answer
The lake water was filtered first to remove suspended (insoluble) solids such as dirt, stones, grit, seeds, and small pieces of plant material, ensuring that only dissolved solids remain in the solution.
Step 2
Name a suitable piece of apparatus to measure accurately 200 cm³ of the filtered water.
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A suitable piece of apparatus would be a burette, a large syringe, or a graduated cylinder.
Step 3
Name the container, A or B, in which the 200 cm³ sample was heated to dryness.
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The container in which the 200 cm³ sample was heated to dryness is container B.
Step 4
Give one safety precaution taken during this part of the experiment.
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One safety precaution is to wear safety goggles to protect the eyes from any potential splashes or heat.
Step 5
Describe a procedure for carrying out a flame test on the solid residue left in A or B.
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Clean a platinum wire by dipping it into hydrochloric acid and then rinsing it with distilled water.
Dip the clean wire into the solid residue from container A or B.
Hold the wire in the flame of a Bunsen burner and observe the colour produced.
A distinct flame colour will indicate the presence of certain metal ions in the residue.
Step 6
What was the mass of dissolved solids in 200 cm³ of filtered water?
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The mass of dissolved solids can be calculated as follows:
Mass of the container and residue = 201.1 g
Mass of the empty container = 135.4 g
Mass of dissolved solids = 201.1 g - 135.4 g = 65.7 g.
Step 7
Calculate the concentration of dissolved solids in grams per litre.
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Concentration can be calculated using the formula:
