How Healthy is Your Water? Objectives: To learn how to analyze water for total dissolved solids, alkalinity and phosphates

Day 1 Three tasks to complete today Determine the pH of the water Filter the water to remove bacteria Initiate the determination of the total dissolved solids in your water

pH of a water sample Acid Rain CO2 dissolves in rain water Low pH water dissolves more minerals (inc Al3+, Pb2+ …) Dissolves the CaCO3 in the shells of crustaceans Disturbs ion balance in fish which lose Na+ through the gills and may ultimately die Little Echo Pond in Franklin, New York. Little Echo Pond has a pH of 4.2

pH tolerance

pH of drinking water Humans and mammals can have a bigger tolerance to the pH of water Soda drinks have pH 2-4. Public water pH 4-9 Public Health Service Act states water needs to be in the range 6.5-8.5 Low pH increase the solubility of Pb, Cu, Zn and Fe metals in pipes!

Procedure for Determining pH Use a pH sensor with the Science Workshop Interface, along with phmeters.sws in the Chem 1B folder on the desktop Calibrate with pH 4 buffer and then pH 7 buffer Determine the pH of your 50-75 mL of your unfiltered sample in a 100 mL beaker

Filtering your Water Sample Before continuing with the analysis you will need to remove any bacteria that could interfere with the subsequent tests This is done in 2 stages Pre-filter about 300 mL with a Buchner funnel first Then filter this 300 mL using a 0.45μm filter

Total Dissolved Solids (TDS) The total amount of dissolved chemical species in water = total dissolved solids Good measure of the concentration of ionic substances present Seawater = 30,000 – 40,000 mg/L Freshwater < 1500 mg/L If an organism is placed in water with low salinity (distilled water) the cells absorb water (osmosis) If an organism is placed in water with high salinity the cell loses water (osmosis) – if it loses too much it may die. High TDS makes water cloudy, inhibits photosynthesis, heats up the water Humans contribute to TDS via runoff from industry, construction, agriculture, logging, sewage treatment discharge

Gravimetric Determination of TDS Label a clean 150 mL beaker with the sample number and your name Place it in a drying oven for 1 hour Then place beaker in desicator until cool weigh beaker Place 50 mL of your filtered water in the beaker and heat just below boiling reducing the volume from 50  10 mL Place beaker in over at 103-105oC till Wednesday

Day 2: Water Analysis Alkalinity 1 drop (0.05mL) of 0.1 M HCl added to 250 mL of distilled water changes the pH from 7 to 4 Natural waters are protected from drastic changes in pH by natural buffers The capacity of water to neutralize acid is called its alkalinity

Alkalinity continued … carbonates, bicarbonates and hydroxides are anions responsible for alkalinity Originate from calcite (CaCO3), magnesite, (MgCO3), dolomites, and brucite (Mg(OH)2) Typical neutralization reactions will be

Measuring Alkalinity Best done by titrating the water with a strong acid (H2SO4) To make life simple assume alkalinity due mainly (solely) to CaCO3 Titrate water with 0.1M H2SO4 with Bromocresol green indicator Titrate till indicator = light green pH = 4 (pH of carbonic acid)

Determining Phosphate Concentration Ammonium heptamolybdate (NH4)6Mo7O24·4H2O or simply as ammonium molybdate (NH4)2MoO4 react with phosphates to form molybdophosphoric acid This reacts with ammonium metavanadata to form the yellow vanadomolybdophosphoric acid complex H3+nPVnMo12−nO40: PVn The intensity of the yellow is proportional to the phosphate concentration

Determining Phosphate Concentration Standardize the Spectrometer Blank, 2, 5, 8 and 10 ppm solutions of the phosphate Measure the absorbance Construct a absorbance vs. concentration curve Compare with your sample