Formaldehyde Standard.doc

RUSSEL GARMENTS 56/1 S.M. MALEH ROAD, OSMAN TOWER, NARAYANGANJ

Preparation & STD of Formaldehyde (HCHO) stock solution General: The stock solution containing approximately 1500µg/ml shall be accurately standardize in order to make precise calibration curve for use in colorimetric analysis .This solution can be prepared by taking 3.8ml of 37% (3,70,000ppm) HCHO solution followed by standardization. Principle: An aliquot of the stock solution is reacted with an excess of Na2SO3 (Sodium Sulfite) followed by back titration with standard H2SO4 (Sulfuric Acid) solution in the presence of THYMOLPHTHALEIN indicator. Apparatus: Burette 50ml, pipette 1ml, 10ml, 20ml, Erlenmeyer flask 250ml. Checking: Check that all the glass wares are washed and dried properly. Also check that all the reagents and reference standards are made properly and the place of working should be clean. Environmental Condition: Cool and dry place. Reagents: 1. 1M Na2SO3 (prepared by dissolving 126g of anhydrous Na2SO3 in 1 L). 2. Thymolphthalein indicator (10g/l in ethanol). 3. 0.01M H2SO4 (take 0.54g or 1ml of conc. H2SO4 in 1L of DW and Standardized). Procedure: 1. Fill the burette with 0.01M H2SO4. Pipette out 50 ml of 1M Na2SO3 in to Erlenmeyer flask. Add two drops of Thymolphthalein indicator. Add a few drops of 0.01M H2SO4, if necessary until the blue color disappears. 2. Pipette 10 ml of the stock HCOH solution to the flask (the blue color will reappear).Titrate the solution with 0.01M H2SO4 until the blue color is discharged. Record the volume of H2SO4 solution used. 3. Carry out the procedure in duplicate. Calculation & Results:

RUSSEL GARMENTS 56/1 S.M. MALEH ROAD, OSMAN TOWER, NARAYANGANJ

1 ml of 0.01M H2SO4 is equal to 0.6 mg of HCHO. Calculate the average of the results and use the accurate concentration in the stock solution (in µg/ml) from the following equation: Formaldehyde (µg/ml) = vol of H2SO4 (ml) x 0.6 x1000 x Ac.con of H2SO4 (M) Volume of sample (ml) x Con. of H2SO4 used (0.01M) No. 1 2 3

Burette reading of H2SO4 Initial volume final volume 0.0

Let, Volume of H2SO4 Volume of sample Actual Con. of H2SO4

Difference

Mean value

= 17.8 ml = 10ml = 0.0098 M (previous find out)

Con. of HCHO, ppm or µg/ml = 17.8 x 0.6 x 1000 x 0.0098 / 10 x 0.01 = 1047. % of HCHO = 37 x 1047 / 1500 = 25.82 %

Approval/ Rejection Criteria: Difference in burette reading for the duplicate analysis should be = +0.1 Con. of Formaldehyde stock Solution should be = 1500µg/ml + 50 Shelf life and Standardization Interval: 1. Shelf life of formaldehyde stock solution is 30 days, after that it should be discarded and fresh solution should be prepared and standardized 2. Standardization of HCOH stock solution should be carried out after every 5 days (max.) if not used. In case of daily usage, it should be standardize before use, each day. Precaution: 1. Before starting work with chemicals, must go through the M.S.D.S. of all the chemicals and follow all the instruction strictly. 2. Wear gloves, goggles, mask, and apron before use of harmful chemicals and use all the chemicals in fume hood. a. In case of any damage or harm, stop the working immediately and inform to supervisor. 1. Preparation of Potassium Hydrogen Phthalate (KHP) soln- 0.01M:

RUSSEL GARMENTS 56/1 S.M. MALEH ROAD, OSMAN TOWER, NARAYANGANJ

2.0422 g KHP was dissolved in 1L DW into a 1L volumetric flax. Molarity of KHP =

W1

Mw x V Here, W1= weight of KHP= 2.0422 g. Mw = Molecular weight of KHP = 204.22 g/mol. V = Volume of KHP = 1 L. So,

Molarity of KHP = 2.0422 / 204.22 x 1 = 0.01 M

2. Preparation of Sodium Hydroxide (NaOH) soln- 0.01M: 0.4g NaOH (Mw = 40 g/mol) dissolved in 1L DW into a 1L VF. Let, 1000ml 1molar solution is 40 g. 1ml 1 ---------= 40 / 1000 x 1. 500ml 0.01 ---------- = 40 x 500 x 0.01 / 1000 x 1 = 0.2 g. 3. Pre. of Phenolphthalein or Thymolphthalein soln (10g/l in Ethanol): 10g Phenolphthalein dissolved in 1L ethanol into a 1L volumetric flax. Or 1g Phenolphthalein dissolved in 100ml ethanol into a 150 ml CF. 4. Titration of Sodium Hydroxide by KHP (0.01M): 10ml Sodium Hydroxide was taken into a conical flax & added 2-3 drops Phenolphthalein solution then titration it by KHP until the pink color change to colorless.

No. 1 2 3

Burette reading of KHP Initial volume final volume 0.0

Difference

Mean value

So, Conc. Of NaOH = Conc. Of KHP x Volume of KHP Volume of NaOH Suppose, Vol. of NaOH = 10 ml, Conc. Of KHP = 0.01M, Vol. of KHP = 10.1 ml So, Conc. Of NaOH = Conc. Of KHP x Volume of KHP Volume of NaOH = 0.01 x 10.1 / 10 = 0.0101M. 5. Preparation of Sulfuric acid (H2SO4) soln- 0.01M:

RUSSEL GARMENTS 56/1 S.M. MALEH ROAD, OSMAN TOWER, NARAYANGANJ

0.54ml of Sulfuric acid was diluted into 100ml DW. 1mol H2SO4 = 98 g. Let, 1000ml 1molar solution is 98 g. 1ml 1 ------------= 98 / 1000 x 1. 1000ml 0.01 ---------= 98 x 1000 x 0.01 / 1000 x 1. = 0.98 g. [100 ml-------------- 98 gm] 98 gm ------------------- = 100 ml 0.98 gm ----------------- = 100 x 0.98 / 98 = 1ml. Specific gravity = 1 / 1.84 = 0.54 ml. 6. STD of Sulfuric acid with NaOH (0.01M): 20ml Sodium Hydroxide was taken into conical flax & added 2-3 drops Phenolphthalein solution then titrate Sodium Hydroxide (0.0101M) by Sulfuric acid (0.01M) until the pink color change to colorless. No. 1 2 3

Burette reading of Sulfuric acid Initial volume final volume 0.0

Difference

So, Conc. of H2SO4 = Strength of NaOH x Volume of NaOH Volume of H2SO4 x 2 Suppose, Volume of NaOH = 20 ml Strength of NaOH = 0.0101M (previous find out) Volume of H2SO4 = 10.3 ml So, Conc. of H2SO4 = Strength of NaOH x Volume of NaOH Volume of H2SO4 x 2 = 0.0101 x 20 / 10.3 x 2. = 0.0098 M.

Mean value