1. How Healthy is Your Water?

2. pH of natural water sources
pH has major consequences for the organisms that live in it
As water becomes more acidic
shells of crustaceans and mollusks weaken
Disturbs balance of Na+, K+, Cl-, Ca2+ in fish
Solubility of Pb, Cu, Zn and Fe in water pipes increase (Plumbing comes from Plumbum and Pb pipes in Rome - till 1986 water pipes in the US contained Pb)
pH of natural water sources

3. Effect of pH on Aquatic Life
Fish cannot survive more than a few hours
pH = 4.0 – 4.5
All fish, most frogs, insects absent
pH =
Many insects absent, most fish eggs won’t hatch
pH = 5.0 – 5.5
Bottom dwelling bacteria die, detritus accumulates, Al, Pb normally trapped in sediment released making water toxic
pH =
Optimal for most organisms
pH = 10.5 – 11.0
Lethal to fish

4. Why is water becoming more acidic?
Acid Rain
Humans are releasing non-metal oxides into the air through combustion of fossil fuels, and coals
𝐻 2 𝑂 (𝑙) + 𝐶𝑂 2 𝑔 ⇌ 𝐻 𝑎𝑞 + + 𝐻𝐶𝑂 3 (𝑎𝑞) −
𝐻 2 𝑂 (𝑙) + 𝑆𝑂 2 𝑔 ⇌ 𝐻 𝑎𝑞 + + 𝐻𝑆𝑂 3 (𝑎𝑞) −
𝐻 2 𝑂 (𝑙) + 𝑆𝑂 3 𝑔 → 𝐻 𝑎𝑞 + + 𝐻𝑆𝑂 4 (𝑎𝑞) −

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

6. Day 1 3 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

7. Procedure for Determining pH
To calibrate the pH you will need
Wash bottle
2 beakers (50—150 mL) on containing pH 7 buffer and one containing pH 4 buffer
Plug pH sensor into the USB port on the LabQuest interface
Calibrate with pH 4 buffer and then pH 7 buffer, by tabbing on Sensor, then Calibrate, choose 2-point calibration
Follow prompts start with pH 4, give 1 min to stabilize, then click keep/apply
Wash the sensor then place it in the pH 7 beaker wait 1 minute for it to stabilize then click keep/apply
Determine the pH of your mL of your unfiltered sample in a 100 mL beaker
Procedure for Determining pH

8. 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

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 30 mins
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

10. Total Dissolved Solids
Total amount of dissolved chemical species in water
Good measure of the concentration of ionic substances in the water
Fresh water: <1,500 mg/L of TDS
Brackish water: 1,500 – 5,000 mg/L of TDS
Seawater: 30,000– 40,000 mg/L of TDS
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, in drinking water it leads to mineral deposits building up on pipes and affect the taste of the water
Humans contribute to TDS via runoff from industry, construction, agriculture, logging, sewage treatment discharge
TDS levels are regulated in drinking water
Total Dissolved Solids

11. 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

12. 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

13. 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)

14. 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

15. 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

16. calcium carbonate (ppm)
Day 3 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

17. 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

18. 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

19. 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

20. 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+]