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

2. 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

3. pH tolerance

4. 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!

5. 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

6. 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

7. Day 1 4 tasks to complete today Determine the pH of the water
Filter the water to remove bacteria
Measure the Alkalinity
Initiate the determination of the total dissolved solids in your water

8. 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

9. 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

10. 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

11. 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 dessicator 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 Monday

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 100mL of your water with 6 drops of bromocresol green with 0.01M H2SO4
Titrate till indicator = light green pH = 4 (pH of carbonic acid)

13. Day 2: Determining Phosphate Concentration
Ammonium molybdate (NH4)2MoO4 reacts with phosphates to form molybdophosphoric acid
Which in turn 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
Using the 20 ppm (mg/L) phosphate standard provided make 25 ml of 1.6, 4.8, 8.0 and 11.2 ppm solutions of the phosphate, (these require 2.00, 6.00, and mL of the 20 ppm phosphate which can be dispensed from one of the two burettes set up in the lab
Put mL of each solution into a 50 mL volumetric flask add a drop of phenolphthalein if pink at 1 drop 6M HCl
Add mL of the vanadate-molybdate solution and fill to the mark with DI water
If pink add 6M HCl drop by drop till clear, then fill up to the calibration mark with DI water
Wait 10 mins for the color to develop
Measure the absorbance at 420 nm
Construct an absorbance vs. concentration curve in Excel and fit a linear trendline
Compare with your sample, by following these steps with 25 mL of your water instead of 25.00mL of the phosphate standard

15. calcium carbonate (ppm)
Day 2 Water Hardness
Water hardness is measured as the sum of calcium and magnesium ions
The [Ca2+]and [Mg2+] can be determined by titration with EDTA
Water Hardness
calcium carbonate (ppm)
designation
0-43
Soft
43-150
Slightly Hard
Moderately Hard
Hard
450
Very Hard

16. Determining Water Hardness
Water hardness can be determined by titrating our water with EDTA
The acid can lose 4H+ and becomes a chelating agent that is hexadentate, complexing with Ca2+ and Mg2+
The endpoint of the titration is when all of the Ca2+ and Mg2+ are complexed with EDTA
To see this we use a special indicator Eriochrome Black T, which forms a very stable wine-red complex, MgIn–, with the magnesium ion
At the end the Mg2+ can no longer complex with the indicator and the solution turns blue-violet

17. Determining Water Hardness
The titration is carried out at pH = 10 to ensure that we have EDTA4+(aq) in solution
EDTA4+(aq) + Ca2+(aq)  CaEDTA2+(aq)
EDTA4+(aq) + MgIn-(aq)  MgEDTA2+(aq)+ In-(aq)
But for the indicator to work there is a little Mg in the indicator to start with, so the end point for us is when it turns violet, not sky blue
End-point

18. Determining Water Hardness
2 titrations
Titrations should agree to within 5% if not do a third titration
Moles EDTA = Moles Ca2+
𝑀 𝑒𝑑𝑡𝑎 × 𝑉 𝑒𝑑𝑡𝑎 = 𝑀 𝐶𝑎 ×5.00𝑚𝑙
𝑀 𝐶𝑎 = 𝑀 𝑒𝑑𝑡𝑎 × 𝑉 𝑒𝑑𝑡𝑎 5.00𝑚𝑙
ℎ𝑎𝑟𝑑𝑛𝑒𝑠𝑠= 𝑀 𝐶𝑎 × 𝑔 𝑚𝑜𝑙
EDTA
250 mL
5.00 mL your water
50 mL DI water
3.0 mL pH 10 buffer
1 mL 1:1 Mg:EDTA
6 drops indicator

19. Ion Exchange Pour a large test tube of resin into a 250mL beaker
Add 50 ml 6M HCl
Stir for 5 mins
Decant liquid into waste container
Add 100ml DI water stir and decant
Check pH of water with pH paper in it is pH < 4 repeat last step, keep washing till the pH of the decanted water is about 4
Place 2 cm of glass wool in bottom 25 mL burette
Transfer contents of beaker into burette washing with plenty of DI water (you may want to have tap open to prevent over filling of the burette. Make sure you always have 1cm or more of water above the resin
Your resin should be about 15 cm in length when settled
Wash with 30 mL DI water – the water’s pH > 4
Pipette 5.00mL of your water into the burette and leave it 5 mins with the tap close
Collect water in a clean dry 250 mL Erlenmeyer flask, when it has drained to surface of resin, start adding DI water, and allow a total of 50 mL to drain through into the flask
Titrate the water in the flask with NaOH and phenolphthalein to determine [H+]