In a school laboratory a group of students carried out investigations on water from a nearby river - Leaving Cert Chemistry - Question 3 - 2015

A brown ring is a positive test for the nitrate ion.

Sulfuric acid (H₂SO₄) is added during the test.

Fertilizer run-off can lead to algal blooms in the water, causing eutrophication. This can result in the water becoming smelly, polluted, and unsuitable for drinking or recreation, as well as harming aquatic life due to decreased oxygen levels.

1. Filter a known volume of river water through filter paper.
2. Pre-weigh the filter paper before the process.
3. Wash the filter paper with distilled water to ensure all solids are collected.
4. Dry and weigh the filter paper again after filtering the water.
5. Calculate the mass of suspended solids by finding the difference in mass before and after the filtration.

1. Use a known volume of previously filtered river water in a clean beaker.
2. Weigh the beaker with water beforehand to know its initial mass.
3. Evaporate the water by applying heat to dry the solids.
4. Re-weigh the beaker after evaporation to find the mass of the remaining solids.
5. The difference in masses gives the concentration of dissolved solids in the water sample. (A labeled diagram would show the beaker with water and the process of evaporation.)

The concentration of suspended solids can be calculated as follows:

dissolved ext{ concentration} = rac{0.03 ext{ g}}{0.5 ext{ L}} = 0.06 ext{ g/L}

For dissolved solids:

(i) The concentration in grams per litre:

dissolved ext{ concentration} = rac{0.13 ext{ g}}{0.2 ext{ L}} = 0.65 ext{ g/L}

(ii) To convert grams per litre to parts per million:

ext{ppm} = 0.65 	ext{ g/L} 	imes 1000 = 650 	ext{ mg/L} 	ext{ (or p.p.m.)}