It is an acid-base titration. The sodium hydroxide is an alkali whose strength changes over time and it can be effectively standardized utilizing primary standard viz. oxalic acid. Sodium hydroxide reacts with oxalic acid in presence of phenolphthalein indicator. The color changes from colorless to pink at the end point.1
Hence, based on the above theory our aim is to prepare and standardize sodium hydroxide using oxalic acid.
Apparatus: Cleaned and calibrated pipettes, Burettes, Conical flasks
Chemicals: Sodium hydroxide AR Grade, Oxalic acid AR Grade, Phenolpthalene indicator
Preparation of sodium hydroxide solution
Molecular weight of NaOH = 40 g
Equivalent weight of NaOH = 40/1 = 40 g
40 g of NaOH dissolved in 1000 ml water = 1N NaOH
20 g of NaOH dissolved in 1000 ml water = 0.5 N NaOH
Preparation of oxalic acid solution
Molecular weight of oxalic acid = 126gm
Equivalent weight of oxalic acid = 126/2=63gm
63 g of oxallic acid dissolved in 1000ml water = 1 N oxalic acid
31.5 g of oxallic acid dissolved in 1000ml water = 0.5 N oxalic acid
Transfer 20 ml of 0.5 N oxalic acid to a conical flask. Add 2-3 drops of phenolphthalein indicator and titrate with sodium hydroxide present in the burette. Note the end point when a pale pink color is observed. Repeat the experiment until three concordant reading.
Tabulation for standardization
|Sl. No.||Volume of Oxalic acid taken (ml)||Burette reading of sodium hydroxide (ml)||Volume of Sodium hydroxide consumed (ml)|
N1V1 = N2V2
N2=Normality of oxalic acid, N1=Normality of NaOH, V2=Volume of Oxalic acid, V1=Volume of NaOH
From the above experiment it was evident that sodium hydroxide can be effectively standardized by using oxalic acid. Addition of phenolphthalein indicator helped in easy detection of the end point. After performing the calculations, strength of the prepared sodium hydroxide solution was found to be……..N.
- Available at: http://www.webhosting.au.edu/basic-science/subjects/chemistry%20lab/experiments/12010/BG%200008-week312010.pdf. Accessed on 23 August 2017.
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