1. Why can’t gravimetric analysis be used to determine the concentration of sodium nitrate (NaNO) in a solution?
2. Why is it important in gravimetric analysis to add an excess amount of precipitating ions to a solution containing an analyte?
3. Relate gravimetric analysis to the phosphorus content in plant food. Include the form in which phosphorus exists in plant food and the ion you could used to precipitate the phosphorus.
1. What Na compound is insoluble? What nitrate is insoluble. You must have an insoluble material to use it gravimetrically.
2. You want to use Le Chatelier's Principle. An excess of the pptng solution will cause the ppt to be less soluble and that leads to more complete pptn.
3. P in plants can get there by being soluble so the plant roots can take it into the system. Soluble P can be determined in fertilizer by pptg it as MgNH4PO4, filter, then fire in an furnace to convert to MgP2O7 (magnesium pyrophosphate), cool and weigh.
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1. Gravimetric analysis relies on the measurement of the mass of a substance to determine its concentration. However, sodium nitrate (NaNO3) is a highly soluble compound in water, meaning it dissolves easily and forms a homogeneous solution. Since gravimetric analysis requires the precipitation of the analyte to form solid particles, the solubility of sodium nitrate prevents the formation of a precipitate that can be collected and weighed accurately.
2. In gravimetric analysis, adding an excess amount of precipitating ions is crucial to ensure complete precipitation of the analyte. By adding an excess of precipitating ions, all of the analyte ions will react with the precipitating ions, leaving no residual analyte in the solution. This leads to quantitative precipitation and helps to avoid errors caused by incomplete or partial precipitation.
3. Gravimetric analysis can be used to determine the phosphorus content in plant food. Phosphorus in plant food usually exists in the form of phosphate ions (PO43-). To precipitate phosphorus from a solution, one could use a suitable precipitating ion such as ammonium molybdate (NH4)2MoO4. The addition of ammonium molybdate to a solution containing the phosphate ions will result in the formation of a yellow precipitate of ammonium phosphomolybdate, which can be collected, dried, and weighed to determine the amount of phosphorus present in the plant food sample.
1. Gravimetric analysis is a technique used to determine the amount of a substance in a sample by measuring its mass. However, it cannot be used to determine the concentration of sodium nitrate (NaNO3) in a solution because gravimetric analysis relies on the formation of a precipitate. In the case of sodium nitrate, it does not readily form a precipitate when added to a solution. Instead, it remains dissolved as individual ions (Na+ and NO3-) in the solution, making it difficult to collect and weigh the precipitate.
To determine the concentration of sodium nitrate in a solution, other analytical methods such as spectrophotometry or ion-selective electrode (ISE) can be used. Spectrophotometry involves measuring the absorption or emission of light by the solution, which is directly related to the concentration of the analyte. ISE relies on the selective response of an electrode to a particular ion present in the solution, allowing for precise measurement of the concentration.
2. In gravimetric analysis, it is crucial to add an excess amount of precipitating ions to a solution containing an analyte. The main reason for this is to ensure complete and efficient precipitation of the analyte.
By adding an excess of precipitating ions (also known as the precipitant or reagent), it ensures that all of the analyte ions are completely consumed in forming the precipitate. This is important because incomplete precipitation would result in inaccuracies in the analysis, leading to incorrect determination of the analyte's mass.
Additionally, adding an excess of precipitating ions helps promote the formation of large, easily filterable precipitates. It reduces the chance of forming small, loosely bound particles that are difficult to filter and retain during the subsequent washing and drying steps of gravimetric analysis.
3. Gravimetric analysis can be used to determine the phosphorus content in plant food. Phosphorus is a vital nutrient for plant growth and is typically present in plant food in the form of phosphates, such as monoammonium phosphate (NH4H2PO4) or diammonium phosphate ((NH4)2HPO4).
To precipitate the phosphorus in plant food for gravimetric analysis, you can use ammonium molybdate ((NH4)6Mo7O24) as the precipitating agent. When ammonium molybdate is added to a solution containing phosphates, it reacts to form a yellow precipitate of ammonium phosphomolybdate [(NH4)3PO4·12MoO3]. This precipitate can then be collected, washed, dried, and weighed to determine the amount of phosphorus present in the plant food sample.
The weight of the resulting precipitate is directly proportional to the amount of phosphorus in the sample, allowing for the determination of phosphorus content through gravimetric analysis.