To prepare different water samples of varying pH and Total Dissolved Solids (TDS) and to determine pH, TDS and electrical Conductivity (EC) of prepared water samples

To prepare different water samples of varying pH and Total Dissolved Solids (TDS) and to determine pH, TDS and Electrical Conductivity (EC) of prepared water samples

Method) DISCUSSION:

The pH of a solution is measured as negative logarithm of hydrogen ion concentration. At a given temperature, the intensity of the acidic or basic character of a solution indicated by pH or hydrogen ion concentration. pH values from 0 to 7 are diminishing acidic, 7 to 14 increasingly alkaline and 7 is neutral. Measurement of pH in one of the most important and frequently used tests, as every phase of water and wastewater treatment and waste quality management is pH dependent. The pH of natural water usually lies in the range of 4 to 9 and mostly it is slightly basic because of the presence of bicarbonates and carbonates of alkali and alkaline earth metais.

PRINCIPLE

The pH is determined by measurement of the electromotive force (cm) of a cell comprising of an indicator electrode (an electrode responsive to hydrogen ions such as glass electrode) immersed in the test solution and a reference electrode (usually a calomel electrode). Contact is achieved by means of a liquid junction, which forms a part of the reference electrode. The emf of this cell is measured with pH meter. Since the pH is defined operationally on a Potentiometric scale, the measuring instrument also calibrated potentiometrically with an indicating (glass) electrode and a reference electrode using standard buffers having assigned pH value

APPARATUS AND EQUIPMENTS

pH meter: Consisting of potentiometer, a glass electrode, a reference electrode and a temperature compensating device. A balanced circuit is completed through potentiometer when the electrodes are immersed in the test solution. Many pH meters are capable of reading pH or millivolt.

Reference electrode: Consisting of a half cell that provides a standard electrode potential. Generally calomel, silver-silver chloride electrodes are used as reference electrode.

Sensor (glass) electrode: Several types of glass electrodes are available. The glass electrode consists essentially of a very thick walled glass bulb, made of low melting point glass of high electrical conductivity, blown at the end of a glass tube. This bulb contains an electrode, which has a constant potential, e.g. a platinum wire inserted in a solution of H+ hydrochloric acid saturated with quinydrone. The bulb is placed in the liquid where pH is to be determined.

Beakers: Preferably use polyethylene or TFE beakers Stirrer: Use a magnetic TFE coated stirring bar.

REAGENTS AND STANDARDS

pH 4 buffer solution: Dissolve 10.12g potassium hydrogen phthalate, KHH4 in distilled water. Dilute to 1L

pll 7 buffer solution: Dissolve 1.361g anhydrous potassium Dehydrogenate phosphate,
KH2PO4, and 1.42g anhydrous disodium hydrogen phosphate, Na2HPO4, which have been dried at 110°C. Use distilled water which has been boiled and cooled. Dilute to IL. pII 9.2 buffer solution: Dissolve 3.8 1 gm borax, Na2B407.10H20 in distilled water, which has been previously boiled and cooled. Dilute to IL.

CALIBRATION

Before use, remove the electrodes from the water and rinse with distilled or dematerialized
water. Dry the electrodes by gentle wiping with a soft tissue. Calibrate the electrode system
against standard buffer solution of known pH, because buffer solution may deteriorate as a
result of contamination, prepare fresh as needed for work or use readily available pH buffers.
Use distilled water a conductivity of less than 2 Siemens at 25°C and distilled and pH 5.6 to
6.0 for the preparation of all standard solutions. For routine analysis, commercially available
buffer tablets, powders or solutions of tested quality also are permissible. Buffer having pH
4.0, 7.0 and 9.2 are available.

pH Meters with Buffer Solutions

PROCEDURE

1. Before use, remove electrodes from storage solutions (recommended by manufacturer)
   
2. Dry electrodes by gently blotting with a soft tissue paper, standardize instrument with electrodes immersed in a buffer solution within 2 pH units of sample pH.
   
3. Remove electrodes from buffer, rinse thoroughly with distilled water and blot dry,
   
4. Immerse in a second buffer below pH 10, approximately 3 pH units different from the first, the reading should be within 0.1 units for the pH of second buffer. (If the meter shows a difference greater than 0.1 pH unit from expected value, look for trouble with the electrodes of pH meter)
   
5. For samples analysis, establish equilibrium between electrodes and sample by stirring sample to ensure homogeneity and measure pH.
   
6. For buffered samples (or those with high ionic strength), condition the electrodes after cleaning by dipping them into the same sample, and read pH.
   
7. With poorly buffered solutions (dilute), equilibrate electrodes by immersing in three or four successive portions of samples. Take a fresh sample and record the pH.
   

Analysis of pH in water Sample

OBSERVATIONS:

(EC) DISCUSSION:
The different HACH Company meter platforms offer direct measurements for TDS; it is up to the operator to select the type of conversion factor that best matches the true TDS value. The TDS is typically used to estimate the amount of total dissolved solids in the sample. The standard method to determine TDS is to filter and evaporate the sample to dryness at 180°C, then weigh the residue. HACH Method 8163 is available for determining the total dissolved solids using the standard method.

To determine the conversion factor for a specific solution of a known TDS value, measure the solution’s conductivity and divide the mg/l TDs value by the conductivity value reported. For example, a solution of a known TDS value of 64 g/L and the measured conductivity value of
100 mS/cm has a conversion factor of 64/100 or 0.64. It is important to know the conversion factor being used, especially when comparing your TDS results with another lab’s results, another test site or when comparing results with previously published or referenced data.

MAINTENANCE:

Due to the nature of the produced and flow back water, the operator needs to be sure to rinse the conductivity cell off with clean water. Do not allow the cell to soak, or store the cell in these samples. Once the cell has been rinsed off, blot and store dry,

PROCEDURE:

1. Press the power On Button.
   
2. Clean the probe with distilled water.
   
3. Give the function (°C. CND, TDS)
   
4. Set the range for CND (as S/cm,mS/m) And for TDS (ns mol, g/L)
   
5. Pour the probe in Sample properly and Note the reading on the display of meter.
6. Conductivity =
   

OBSERVATION: