12. Estimation of sodium and potassium present in water using flame photometer

12. ESTIMATION OF SODIUM AND POTASSIUM PRESENT IN WATER USING FLAME PHOTOMETER

Expt. No.

Date:

AIM

To estimate the amount of sodium and present in the given water sample using flame photometer.

PRINCIPLE

Flame photometry (or) Flame Emission Spectroscopy is based on the principle of emission of certain radiation in the visible region by a metal atom.

In this technique metal atom is thermally excited from the ground state. The excited atom emits light of particular intensity while returning to the ground state depending upon the concentration of the metal ions.

A water sample to be analysed is sprayed into the flame, where the water evaporates leaving the fine salt particles. This salt decomposes into constituent atoms, when they are heated to about 1700°C. The vapours containing metal atoms are excited by the thermal energy of the flame to higher energy state.

When the electrons fall down from the excited state to ground state, they emit radiation. The emitted radiation is measured and recorded.

The emission spectrum for each metal is different and its intensity depends on the concentration of the atoms in the flame.

Sodium produces a characteristic yellow emission at 589 nm.

Potassium produces a characteristics red emission at 766 nm.

Different standard solutions (say 1, 2, 4, 6, 8 & 10 ppm ) are prepared and the calibration curve is drawn between concentration (ppm) Vs intensity of emitted light (photometric readings).

PROCEDURE

Step l: Preparation of stock Na+ ion solution

A stock solution of Na⁺ ion is prepared by dissolving 25.4 gms of NaCl in 1 litre of distilled water.

1 ml of stock solution = 10 ppm of Na⁺ ion

From the stock solution, various concentrations are prepared (1, 2, 4, 6 and 8 ppm) as shown in table I.

Step II: Preparation of stock k solution

A stock solution of K⁺ is prepared by dissolving 1.809 gms of KCI in 1 litre of distilled water.

1 ml of stock solution = 1 ppm of K⁺

From the stock solution various concentrations are prepared (1, 2, 4, 6 and 8 ppm) as shown in table II.

Step III: Working with instrument

The instrument is switched on. Air supply and gas supply are regulated. First distilled water is sent and ignition is started. After the instrument is warmed up for 10 min, the instrument is adjusted for zero reading in the display.

 (a) Determination of sodium in the water sample.

NaCl solution of 8 ppm is sent and the reading is adjusted for 100. Now the instrument is said to be calibrated.

The solution of NaCl of other known concentrations (1, 2, 4 6 and 8 ppm) is sent one by one and the reading (intensity of emitted light) is noted. The calibration graph is drawn between the concentration Vs. intensity of the emitted light (readings).

Now the unknown water sample is sent and the intensity of emitted light (reading) is noted. Then the concentration of sodium in the water sample is determined from the calibration curve.

(b) Determination of potassium in the water sample

KCI solution of 8 ppm is sent and the reading is adjusted for 100. Now the instrument is said to be calibrated.

The solution of KCl of other known concentration (1, 2, 4 and 6 ppm) is sent one by one and the reading is noted as before. The calibration graph is drawn between the concentration Vs readings.

Now unknown water sample is sent and the reading is noted. Then the concentration of potassium in the water sample is determined from the calibration curve.

RESULT

(a) The amount of sodium present in the water sample = …….. ppm

(b) The amount of potassium present in the water sample = …….. ppm