Lab 1: LANGeLIERS index [Document subtitle]
Water and Environmental
Sean O’Brien
C14738175
20/October/2016
Aim of experiment
The aim of the Langeliers index experiment is to test three water samples and calculate the Langaliers
index of all three at 19° and 80°C.
The index shows if a water sample is corrosive, degrading metal in pipes, or if the sample is scaling,
causing scale build up in pipes with no corrosion.
Parameters measured
pH. - The level of acidity or basicity of the supply on the scale of 1 – 14.
Temperature – Temperature of sample at time of experiment, measured in degrees Centigrade.
Alkilinity - The capability of the sample to neutralize acid. Measured in mg/l.
Hardness - Hardness of the sample is the amount of dissolved calcium present. Measured in mg/l.
Total Dissolved Solids - These are all the minerals, salts, metals and anions dissolved in the sample.
Measured in mg/l.
Sources of Calcium/alkalinity in drinking water
Alkalinity of water depends on the number of ions. These include hydroxide, carbonates and
bicarbonates.
The cause of Hardness in water is the amount of calcium and magnesium present.
“Water alkalinity and hardness are primarily a function of 1) the geology of the area where the surface
water is located and 2) the dissolution of carbon dioxide (CO2) from the atmosphere. The ions
responsible for alkalinity and hardness originate from the dissolution of geological minerals into rain and
ground water. Rainwater is naturally acidic, which tends to solubilize some minerals more easily. Surface
and ground water sources in areas with limestone formations are especially likely to have high hardness
and alkalinity due to the dissolution of bicarbonates and carbonates.”1
1
http://edis.ifas.ufl.edu/ss540
Experimental Method
The class split into groups to carry out the experiments. The experiment covered in this report is
alkalinity. In addition, the results obtained from the other experiments are collected. The results form
the derivation of Langeliers index.
The measure of alkalinity of the sample method is as follows. Place 100ml of sample in beaker with pH
electrode. Titrate HCl solution into the beaker in steady amounts. Stop when reaching a pH of 4.5.
Take amount of HCl solution added at 4.5. Add this value into formula supplied. With the result. Read a
value of the table for Log Alkalinity. Use this value form table Log Alkalinity in pHs formula.
Experimental Results Table
Burette reading PH Value mls Added pH Required
Initial Values 0.02 8.03 0 4.5
0.2 7.69 0.18 4.5
0.38 7.35 0.18 4.5
0.52 7.21 0.14 4.5
0.72 6.97 0.2 4.5
0.88 6.84 0.16 4.5
1.12 6.71 0.24 4.5
1.38 6.58 0.26 4.5
1.72 6.4 0.34 4.5
2.2 6.18 0.48 4.5
2.7 5.91 0.5 4.5
3.18 5.48 0.68 4.5
3.56 4.46 0.38 4.5
pH Sample vs mls HCL added
8.5
7.5
6.5
6
pH
5.5
4.5 4.46
3.5
0 0.5 1 1.5 2 2.5 3 3.5 4
mls Added
Experimental Results Calculations
3.56ml x 0.1M x
→
Alkalinity AS mg/l CaCO3 = A x N x 50,000 50,000
ml of sample → 100ml
178 mg/l
Alkalinity AS mg/l CaCO3 = CaCO3
Results Table 1
Water Temp. Alkanlinit Hardnes TDS(g/ TDS
pH
Source °C y mg/l s mg/l dl) (mg/l)
Kildare 7.96 19 178 278 0.0445 445
Tipperary 7.5 19 264 324 0.0106 106
Blackrock 7.34 19 35 70 0.2379 2379
Calculation of Langeliers index based on Results
Is (Lang.index) = pH – pHs
pHs = A + B – Log[Ca++] – Log [Alk.]
Kildare @ 19°C Kildare @ 80°C
pHs = 2.125 + 9.863 – 2.44 – 2.234 = 7.314 pHs = 1.15 + 9.863 – 2.44 – 2.234 = 6.339
Is = 7.96 – 7.314 = 0.646 Is = 7.96 – 6.339 = 1.620
Tipperary @ 19°C Tipperary @ 80°C
pHs = 2.125 + 9.77 – 2.508 – 2.415 = 6.972 pHs = 1.15 + 9.77 – 2.508 – 2.415 = 5.997
Is = 7.50 – 6.972 = 0.528 Is = 7.50 – 5.997 = 1.503
Blackrock @ 19°C Blackrock @ 80°C
pHs = 2.125 + 9.900 – 1.84 – 1.54 = 8.645 pHs = 1.15 + 9.900 – 1.84 – 1.54 = 7.670
Is = 7.34 – 8.645 = -1.305 Is = 7.34 – 7.670 = - 0.33
Results Table 2 and Index
LSI (Carrier) Indication
-2,0 < -0,5 Serious corrosion
-0,5 < 0 Slightly corrosion but non-scale forming
LSI = 0,0 Balanced but pitting corrosion possible
0,0 < 0,5 Sligthly scale forming and corrosive
0,5 < 2 Scale forming but non corrosive
Water Source Temperature Lang.Index Obtained Indication
Kildare 19°C 0.646 Scale forming, non-
corrosive
80°C 1.642 Scale forming, non-
corrosive
Tipperary 19°C 0.528 Scale forming, non-
corrosive
80°C 1.503 Scale forming, non-
corrosive
Blackrock 19°C -1.305 Serious Corrosion
80°C -0.330 Slight Corrosion, non-scale
forming
http://www.lenntech.com/calculators/langelier/index/langelier.htm#ixzz4OyDqJFKE
Significance/Conclusion of Langeliers indication
The first two water sources have scale-forming water. These supplies will form a scale on metal pipes
and offer protection. If the water is heated to high temperature, it may cause buildup of scale.
The BlackRock supply shows a corrosive water that will wear down any metal elements in contact with
it. If this water is heated, though it becomes more neutral and less corrosive.
By observing the results, the BlackRock supply contains soft water. This water is naturally low in
hardness and alkalinity therefore it has not reaches it saturation point for CaCo3. This leads the water to
stripping the pipes as it passes through which in turn leaves it higher in TDS than the other water
supplies.
References
http://www.lenntech.com/calculators/langelier/index/langelier.htm#ixzz4OyDqJFKE
http://edis.ifas.ufl.edu/ss540
https://www.epa.ie/pubs/advice/water/quality/Water_Quality.pdf
