Why HNO3 only can used for acidification in volhard method not other acids like HCl or H2SO4?
Because the Ag^+ will ppt with AgCl and Ag2SO4 is rather insoluble, also.
HNO3 is typically used for acidification in the Volhard method due to its unique properties that make it suitable for this particular analysis. Here are the reasons why HNO3 is preferred over other acids like HCl or H2SO4 in the Volhard method:
1. Stability of Silver Nitrate: In the Volhard method, the analyte is titrated with a standard solution of silver nitrate (AgNO3). HNO3 is preferred as the acidifying agent because it does not interfere with the stability of the silver nitrate solution. Other acids like HCl or H2SO4 may react with silver ions, forming insoluble silver chloride (AgCl) or silver sulfate (Ag2SO4), respectively. This would lead to inaccurate determination of the analyte concentration.
2. pH Control: HNO3 provides the appropriate pH for the Volhard method. The acidification step is necessary to dissolve any excess silver precipitate formed during the titration. HNO3 maintains the solution at a pH range of approximately 2-3, which is optimal for redissolving the silver chloride precipitate without causing further precipitation or interfering with subsequent reactions.
3. Selectivity for Halides: The Volhard method is primarily used for the determination of halide ions, such as chloride (Cl-), bromide (Br-), and iodide (I-). HNO3 does not react with these halide ions, allowing for accurate quantification. On the other hand, HCl and H2SO4 can react with halide ions, leading to the formation of different compounds and interfering with the analysis.
In summary, HNO3 is preferred for acidification in the Volhard method because it exhibits stability with silver nitrate, provides the necessary pH, and does not interfere with the halide ions being analyzed.
In the Volhard method, acidification is required to convert any chloride ions present in a solution to silver chloride precipitate. This is essential for accurately determining the concentration of chloride ions in a sample.
HNO3 (nitric acid) is the preferred acid for acidification in the Volhard method due to several reasons:
1. Oxidizing Agent: HNO3 is a strong oxidizing agent, it can convert any Fe(II) ions that may be present in the sample to Fe(III) ions. This conversion is necessary for the subsequent reaction with silver ions.
2. Volatility: HNO3 is a volatile acid, meaning it can be easily evaporated during subsequent steps of the Volhard method. This is beneficial as it helps in removing excess acid and other volatile compounds, leaving behind the desired precipitate.
3. Insolubility: When AgNO3 (silver nitrate) is added as a reagent in the Volhard method, it reacts with chloride ions to form silver chloride precipitate. Unlike other acids, such as HCl (hydrochloric acid) or H2SO4 (sulfuric acid), HNO3 does not interfere with the formation of silver chloride. Other acids may react with AgNO3 to form other unwanted precipitates or soluble salts, hindering accurate measurement.
Therefore, HNO3 is the acid of choice for acidification in the Volhard method due to its oxidizing properties, volatility, and compatibility with silver chloride precipitation.