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You have performed first-hand investigations on water samples using qualitative and quantitative analyses - HSC - SSCE Chemistry - Question 21 - 2004 - Paper 1
Question 21
You have performed first-hand investigations on water samples using qualitative and quantitative analyses. (a) Distinguish between qualitative analysis and quantita... show full transcript
Worked Solution & Example Answer:You have performed first-hand investigations on water samples using qualitative and quantitative analyses - HSC - SSCE Chemistry - Question 21 - 2004 - Paper 1
Step 1
Distinguish between qualitative analysis and quantitative analysis.
Answer
Qualitative analysis refers to the determination of the presence or absence of particular substances within a sample. It focuses on identifying the chemical constituents present in the sample without measuring their quantities. In contrast, quantitative analysis involves measuring the exact amount or concentration of those substances, providing numerical data that allows for a detailed understanding of the composition of the sample.
Step 2
Describe TWO factors that affect the concentrations of ions in natural bodies of water.
Answer
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Runoff and Pollution: The concentration of ions in natural bodies of water can be significantly influenced by runoff from agricultural or urban areas, where fertilizers, pesticides, and other chemicals enter water sources, increasing the levels of ions like nitrates and phosphates.
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Evaporation and Salinity: In areas with high evaporation rates, such as lakes in arid regions, the concentration of ions can increase as water evaporates, leaving behind salts and minerals, thus raising the salinity of the body of water.
Step 3
Complete the following table to show how the anions listed can be identified.
Answer
| Anion | Reagent | Observations if anion is present |
|---|---|---|
| Cl^- | Silver nitrate (AgNO₃) | A white precipitate of silver chloride (AgCl) forms. |
| PO_4^{3-} | Ammonium molybdate | A yellow precipitate of ammonium phosphomolybdate forms. |
| SO_4^{2-} | Barium chloride (BaCl₂) | A white precipitate of barium sulfate (BaSO₄) forms. |