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standardising sodium hydroxide

Standardizing Sodium Hydroxide A Crucial Process in Analytical Chemistry

Sodium hydroxide (NaOH), commonly known as caustic soda, is a key reagent in various chemical processes and analytical applications. It is a strong base and is widely used in laboratories for titrations, pH adjustments, and in the synthesis of different compounds. However, the concentration of sodium hydroxide solutions can change over time due to factors such as evaporation, absorption of moisture, and impurities. Therefore, standardizing sodium hydroxide is essential to ensure accurate and reliable results in analytical chemistry.

Standardization is the process of determining the exact concentration of a solution. For sodium hydroxide, this typically involves titrating it against a primary standard, which is a highly pure substance with a known concentration. A commonly used primary standard for this purpose is potassium hydrogen phthalate (KHP, KHC8H4O4). KHP is advantageous because it is stable, non-hygroscopic, and has a well-defined molecular weight, making it ideal for use in standardization procedures.

The procedure for standardizing sodium hydroxide using KHP involves several steps. First, a known mass of KHP is accurately weighed and dissolved in distilled water. The NaOH solution of unknown concentration is then titrated against the KHP solution. During the titration, the point at which the reaction is complete is determined using a suitable indicator, such as phenolphthalein, which changes color at pH values around 8.2 to 10.0, indicating the transition from acidic to slightly basic conditions.

The reaction between NaOH and KHP can be represented by the balanced equation

\[ \text{KHP (aq) + NaOH (aq) → NaKP (aq) + H2O (l)} \]

From the balanced equation, it is clear that one mole of KHP reacts with one mole of NaOH. Therefore, by measuring the volume of NaOH solution required to reach the endpoint of the titration, the concentration of the sodium hydroxide solution can be calculated using the formulas

standardising sodium hydroxide

\[ \text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}} \]

After performing the titration, the average volume of NaOH used can be used to calculate its molarity. If, for example, 0.1 grams of KHP (with a molar mass of approximately 204.22 g/mol) were used and the average volume of NaOH required was 25.0 mL (or 0.025 L), the calculation would be as follows

1. Calculate moles of KHP \[ \text{Moles of KHP} = \frac{0.1 \text{ g}}{204.22 \text{ g/mol}} \approx 0.00049 \text{ moles} \]

2. Since the stoichiometry shows a 11 ratio, moles of NaOH will also be 0.00049.

3. Calculate the molarity of NaOH \[ \text{Molarity of NaOH} = \frac{0.00049 \text{ moles}}{0.025 \text{ L}} \approx 0.0196 \text{ M} \]

By following this process, chemists can ensure their sodium hydroxide solution is accurately standardized, leading to high-quality results in subsequent experiments and analyses.

In conclusion, standardizing sodium hydroxide is a fundamental procedure that plays a critical role in analytical chemistry. This process not only enhances the accuracy of titrations but also ensures that conclusions drawn from experiments are based on reliable data. As sodium hydroxide continues to be a vital component in a range of chemical applications, understanding and implementing the standardization process remains crucial for scientists and researchers in the field.

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