Determining the concentration of sodium and potassium in water sample using flame photometer

DETERMINING THE CONCENTRATION OF SODIUM AND POTASSIUM IN WATER SAMPLE USING FLAME PHOTOMETER

AIM:-To determine the concentration of sodium and calcium using flame photometer.

APPARATUS:- Flame Photometer.

THEORY:- Sodium, potassium and calcium are abundantly available in nature and their salts are highly soluble in water. Hence most of the water samples contain these elements in varying quantities depending upon the source of water. Even though, they are harmless in small quantities, excessive concentrations may impart a bitter taste to water and may make the water hazardous  to the health of cardial and kidney patients. Sodium is corrosive to metals surface and in large concentrations it is toxic to plants.

            The principle of working of flame photometer is very simple. The sample is sprayed as fine mist into non-lumbinous flame which becomes coloured depending upon the characteristics of the emissions of the elements present in the sample water. The equipment has two channels which work simultaneously. Each channel has a detective device which views the flame through a narrow band optical filter that only passes the wave lengths centered around the characteristics emissions of the selector element. For sodium, this wave length is 589nm and for potassium it is 768nm. The output of the detector is passes on to an electronic metering device which converts the input to a digital readout

            Concentrations in the range of 0-2m.eq. per lit of sodium and 0-0.1m.eq.per lit of potassium can be measured with the equipment after calibration.

RELAVANCE:- Potassium is a major chemical constituent of potable water. The average level of sodium is greater than 100mg/lit. Higher amounts of sodium render boiler operations difficult. High concentration of sodium in blood leads to hyper tension. Soil permeability can be affected by concentration of sodium. Potassium is generally not found in water in high concentration. The ratio of sodium to potassium is generally 10:1 to 20:1.

CHEMICAL REAGENTS:

i)                    Deionized water

ii)                  Sodium chloride

iii)                Potassium chloride

PROCEDURE:-

a) Calibration of the flame photometer:-

i)                    Prepare 1000ppm Nacl solution by dissolving 2.5416 grams of Nacl salt in 1.0 lit of deionozed water. Using this stock solution, prepare a standard solution of 1.0m.eq.per lit (1.0m.eq./lit=23ppm)

ii)                  Prepare 1000ppm Kcl solution by dissolving 1.907 grams of Kcl salt in 1.0lit of deionized water. Using this stock solution, prepare standard solution of 0.08m.eq.’lit(1.0m.eq/lit=39ppm). These two standard solutions are used for the calibration of equipment.

b) Procedure:-

1. Switch on the power supply and allow the instrument to warm up for about 5 mins.
2. Switch on the air compressor and set the pressure between 0.3-0.6 kg/cm2
3. Light the flame and adjust the gas supply so that a low intensity blue flame is obtained.
4. Set all the coarse and fine controls to the maximum position and select the sodium and potassium filters.
5. Feed deionized water to atomizer and wait atleast for 30 seconds.
6. Adjust the “Set Reference” course and fine controls for zero readout for potassium and sodium.
7. Aspirate 1.0m.eq/lit. of sodium solution and wait at least 30 seconds and then adjust the “set F.S” course and fine controls for a readout of 100 for sodium only.
8. Aspirate 0.08m.eq/lit. of potassium solution and wait atleast 30 seconds and then adjust the “set F.S” coarse and fine control for a readout of 80 for potassium only.
9. Repeat steps 6 to 8 until the readings are stabilized the equipment now stands calibrated.

c) Determination of sodium and potassium concentration in the given sample water:-

Feed the sample to the atomizer and obtain the readings corresponding to sodium and potassium. If the concentrations of sodium and potassium in the sample water is more than the measurable limit of the equipment, the unit will not show a meaningful display. In that case the sample has to be diluted so as to get a meaningful digital read out. Note down the extent of dilution of the sample (i.e. dilution factor). Let 10ml of sample water is diluted to 50ml by adding deionozed water. Let the readings be 62 and 31 for sodium and potassium respectively.

Specimen calculations:

Dilution factor = ml of diluted sample   =  50  =  5

                             ml of sample                   10

Concentration of sodium

in mg/lit                                   =  62*1*23*5 = 71.3 mg/lit

                                                   100

Concentration of potassium

in mg/lit.                                  = 31 *0.08*39*5  = 6.045 mg/lit

                                                    80

OBSERVATIONS:-

Sample No.	Digital readout for		Dilution factor
	Na	K

CALCULATIONS:-

RESULTS:-

INTERPRETATION OF RESULTS:-