CHEMICAL MONITORING & MANAGEMENT LESSON 6: WATER QUALITY 1 SAMPLE RESOURCES

Transcription

1 YEAR 2 CHEM ISTRY CHEMICAL MONITORING & MANAGEMENT SAMPLE RESOURCES

2 YEAR 2 CHEMISTRY. Water Quality Students perform first hand investigations to use qualitative and quantitative tests to analyse and compare thee quality of water samples. Clean water is an essential resource. When might water quality be important? Due to the importance off clean water, most countries havee government organisations in chargee of monitoring and managing their water systems. What Influences Water Quality? Water quality is highly dependent on the surrounding environment Page 80 of 334

3 YEAR 2 CHEMISTRY Water quality is influenced by human activities, such as land clearing, agriculture, urban and industrial activity, and ecreational use. What substances might be added to a bodyy of water by human activity? 2 Natural phenomena such as changing weather patterns and the presence of wildlife will also affect water quality. By 80 trading 24 (Own work) [CC BY-SA Wikipedia [CCC BY 3.0 ( via Wikimedia Commons 3.0 ( via Wikimedia Commons Mrcricket48 at English By Kingbob86 (Timothy) ( [CC BY 2.0 ( via v Wikimedia Commons What substances might be added to a bodyy of water by different weather phenomena? 3 The location of the water has a large impact on its composition and characteristics. Generally, water quality is best at the headwater source. Water quality often declines as it flows through areas of human activity. Rivers can carry substances large distances before discharging into the ocean. 207 Page 8 of 334

4 YEAR 2 CHEMISTRY Types of Water Match the type of water with its description. 4 Drinking water, Fresh water, Greywater, Groundwater, Industrial discharge, Irrigation water, Rainwater, Sea water, Sewage, Stormwater, Surface water Water Description Water found beneath the Earth s surface, in the spaces between rocks and soil. Large reservoirs are known as aquifers. All water that is exposed to the Earth s atmosphere, including water in lakes, rivers, streams, oceans. Naturally occurring water that contains low concentrations of salts and other dissolved solids. Typically found in rivers, lakes, ponds, bogs, ice sheets, glaciers and groundwater. Also known as saltwater, and is found in seas and oceans. It is denser than pure and fresh water due to the presence of dissolved salts. Water collected from roof runoff. As it has minimal surface contact, it is generally relatively free of impurities, especially in non-urban areas, and is sometimes collected for drinking. Urban surface water runoff after heavy rain. Its quality and quantity can vary greatly. Water of a quality suitable for consumption, cooking and bathing. Also called potable water Water discharged into the sewerage network. Consists of greywater and toilet water, and must be treated before it is released into the environment or reused. Also known as wastewater. Household water from baths, showers, laundries and kitchens. May contain pathogens, nutrients and other contaminants. Water that has been artificially diverted to assist in growing vegetation. Water that is released into the environment after use in industry, such as for cooling. Contamination with industrial waste is carefully monitored. 207 Page 82 of 334 this publication may be reproduced, stored in or introduced into a retrieval system, or transmitted, in any

5 YEAR 2 CHEMISTRY 2. Monitoring Water Quality Students learn to identify factors that affect the concentrations off a range off ions in solution in natural bodies of water such as rivers and oceans Water quality refers to the characteristics andd composition of a sample of water. Water quality can be monitored qualitatively or quantitatively. Monitoring qualitatively involves using human senses to check for colour transparency odour taste Qualitatively analyse these water samples (make a guess if you don tt know): Property Colour Transparency Odour Taste Sydney Tap Water Cooks Riverr (Inner Sydney) 207 Page 83 of 334

6 YEAR 2 CHEMISTRY Account for f any differences in your analyses of the two water samples. 5 Account for f the low quality of water from the Cooks River. 6 Although qualitative analysis is insightful, in order to effectively monitor and manage water sources, it is necessary to quantify the extent of the pollution with analytical techniques that can determinee water quality. By Biatch33 (Own work) [Public domain], via Wikimedia W Commons Monitoring quantitativelyy involves using chemicals or equipment to measure: turbidity total dissolved solids (TDS) concentration of common ions chemical hardness (Ca 2+ and Mg 2+ ) heavy metals (e.g. Hg, Pb and Cd) acidity dissolved oxygen (DO) biochemical oxygen demand (BOD) nitrogen-to-phosphorus ratio 207 Page 84 of 334

7 YEAR 2 CHEMISTRY 3. Turbidity Students learn to identify that water quality can be determined by b considering turbidity Students perform first hand investigations to use qualitative and quantitative tests to analyse and compare the quality of water samples. Turbidity Turbidity is a measure off water clarity. Suspended solids in water can scatter light, which makes the water appear cloudy or murky. Causes of water turbidityy include soil runoff from earth disturbances (clay, silt, sand), plankton, microbes, plant matter, industrial waste and sewage. Turbidity often increasess sharply after heavy rain. High turbidity in waterways is problematic for several s reasons. The penetration of sunlight, essential for photosynthep esis by aquatic plants, can be reduced by turbidity. Small particles in thee upper layers of a water body cann absorb infrared radiation from sunlight, raising water temperature. Particles can clog fish gills, which leads too disease, slowed growth and impeded egg and larval development. Predators which require light to find food will w also die off. 207 []Public Domain] Page 85 of 334

8 YEAR 2 CHEMISTRY Measuring Turbidity Turbidity can be measured visually using a Secchi disk or turbidity tube, electronically by using ann electronicc turbidity meter or by gravimetric means. A Secchi disk is a plastic disk with alternating black and white segments, mounted ontoo a rod. It is lowered into a body off water until the mark on it can no longer be seen, and the depth is recorded. The greater the turbidity, the more quickly the t mark will disappear. This method has limited accuracy as glare from the water s surface can cause errors, and it is highly dependent on the eyesight of the observer. A very similarr method is the use of a turbidity tube. 207 Page 86 of 334

9 YEAR 2 CHEMISTRY Using the diagram, briefly outline how a turbidity tube would be used. 7 A more accurate measurement can be obtained by using a turbidity meter. A sample of water is placed in front of a light source. The intensity of light scattered by thee particles in the sample is measured, giving a reading in nephelometric turbidity units (NTUs). 207 Page 87 of 334

10 YEAR 2 CHEMISTRY However, turbidity meters are expensive (~ ~$000), which limits their usefulness. The total suspended solids in a water sample can c also be determinedd by filtering the water sample, providing the filter paper p has suitably small pores. Drying and weighing the filtered solids then allows the total quantity of suspended solids to be determined (gravimetricc analysis). Concept Check 3. (i) Explain what is meant by the term turbidity, with respect to water. 8 (ii) Discuss any detrimental effects resulting from high readings of turbidity Page 88 of 334