Prelab 3 PDF

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EXPERIMENT NO 3: NEUTRALIZATION SEQUENCE AND POTENTIOMETRIC TITRATIONS. OBJECTIVE  To standardize sodium hydroxide  To standardize HCl  To perform soda ash unknown solution titration EQUIPMENT AND CHEMICALS 

150ml Beakers

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250ml Volumetric flask

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1L Volumetric flask

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Boston bottle

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Analytical balance

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Glass Funnel

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250ml Erlenmeyer flask

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250ml Pipette

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50ml Burette

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pH meter

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Graduated cylinder

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6M HCl

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NaOH

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Distilled water

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Potassium Hydrogen Phthalate (KHP)

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Soda ash

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Phenolphthalein indicator

PROCEDURE PREPARATION OF 0.1M HCL 1. Fill 1L of volumetric flask with 500ml quantity of distilled water. 2. Measure 17.5ml of 6M HCl with the help of graduated cylinder. 3. Transfer in volumetric flask and fill the flask up to volume with distilled water. 4. Transfer to the Boston bottle and marked it as “HCl-0.1M”.

PREPARATION OF 0.1M NAOH 1. Weigh 4.2g of NaOH and add to the 1L volumetric flask filled with 500ml water. 2. Bring the flask up to volume with distilled water and mix the solution 3. Cool down to room temperature. 4. Mark as “NaOH-0.1M”. STANDARDISATION OF 0.1M NAOH 1. KHP is weighed by difference with the help of analytical balance. 2. Four samples of KPH weighing within the range of 0.6-0.8g are poured into 250ml flask. 3. Weight of KPH is noted down. 4. Mix 50ml of water. 5. Add 3 to 4 drops of phenolphthalein indicator to each. 6. Wash 50 ml of burette with 0.1M NaOH solution and then completely fill the burette with this solution, without any air bubble. 7. Titration is performed until faint pink color in flask is achieved. 8. Volume of NaOH used is recorded (2 decimal places). 9. Molarity is calculated for each titration and mean of three values should be 0.0003M. STANDARDISATION OF 0.1M HCL 1. Rinse 25ml volumetric pipette with 0.1M HCl solution and pipette 25ml sample into 3 250ml Erlenmeyer flask. 2. Add 50ml distilled water and add 2 to 3 drops of phenolphthalein indicator. 3. Perform titration with standardized solution of NaOH till faint pink color is achieved. 4. Note values. Molarity is calculated and average of three values should be between -0.1 to +0.1 ml. SODA ASH UNKNOWN SOLUTION 1. Weigh 4-4.5g of dried soda ash unknown 2. Put into funnel placed in volumetric flask.

3. Add water and mix.

DIRECTIONS FOR THE USE OF pH METRE 1. pH with combined electrode is used with proper tip. 2. Plug in and calibrate in fresh pH buffer liquid. 3. Wash and dry electrodes when liquid is exchanged. TITRATION OF SODA ASH UNKNOWN SOLUTION 1. Add 25ml of sodium carbonate solution using 25ml pipette into 150ml beaker. 2. Add 50ml water with 3 drops of phenolphthalein indicator and use a magnetic stirrer. 3. Decrease the pH into beaker by starting the stirring bar. 4. First inflection point occurs where indicator becomes colorless and pH decreases. 5. 0.2ml of HCl is added depending on pH of the solution to obtain second inflection point which occur double the volume of first inflection and will depict rapid change in pH but no color change. pH is analyzed by adding small volumes of HCl. Thus, results are plotted....