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

2. 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

3. 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

4. pH tolerance

5. 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
Low pH increase the solubility of Pb, Cu, Zn and Fe metals in pipes!

6. 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 mL of your unfiltered sample in a 100 mL beaker

7. 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

8. 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

9. 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 oC till Wednesday

10. 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

11. 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

12. 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)

13. 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

14. 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