Gravimetric Analysis: the Determination of Phosphorus in Plant Food
Gravimetric Analysis:
The Determination of Phosphorus in Plant Food
Gravimetric analysis is a quantitative (i.e. how much?) method of classical analysis. The element to be determined is isolated in a solid compound of known identity and definite composition. The mass of the element that was present in the original sample can be determined from the mass of this compound. Plant foods contain three essential nutrients that are not readily available from soils. These are soluble compounds of nitrogen, phosphorus, and potassium. A typical label on a plant food will have a set of numbers such as 15-30-15. These numbers mean that the plant food is guaranteed to contain at least 15% nitrogen, 30% phosphorus (expressed as P2O5) and 15 % potassium (expressed as K2O). The remaining of the product is fillers, dyes and other anions and cations to balance the charge in the chemical compounds. In this experiment, we will illustrate a quality control analysis for the determination of phosphorus in plant food by gravimetric analysis. Phosphorus will be determined by precipitation of the insoluble salt magnesium ammonium phosphate hexahydrate according to the reaction: 5H2O(l) + HPO42-(aq) + NH4+(aq) + Mg2+(aq) + OH-(aq) ( MgNH4PO4 . 6H2O(s)
The % P and % P2O5 in the initial sample can be calculated from the mass of MgNH4PO4 . 6H2O obtained using the following method:
mass of MgNH4PO4 .. 6H2O ( moles of MgNH4PO4 .. 6H2O ( moles of P ( mass of P ( %P and mass of MgNH4PO4 .. 6H2O ( moles of MgNH4PO4 .. 6H2O ( moles of P ( moles of P2O5 ( mass of P2O5 ( %P2O5
Prelab Questions
1) Create an organized data table that will include every piece of data for both samples.
2) If a fertilizer says 10-15-10, what does it mean?
3) If a 3.45 g sample of fertilizer is found to form 2.73 g of MgNH4PO4 . 6H2O using the method below, determine the percent of phosphorus, and the percent of P2O5.
Procedure
Prepare 2 samples per group
The Determination of Phosphorus in Plant Food
Gravimetric analysis is a quantitative (i.e. how much?) method of classical analysis. The element to be determined is isolated in a solid compound of known identity and definite composition. The mass of the element that was present in the original sample can be determined from the mass of this compound. Plant foods contain three essential nutrients that are not readily available from soils. These are soluble compounds of nitrogen, phosphorus, and potassium. A typical label on a plant food will have a set of numbers such as 15-30-15. These numbers mean that the plant food is guaranteed to contain at least 15% nitrogen, 30% phosphorus (expressed as P2O5) and 15 % potassium (expressed as K2O). The remaining of the product is fillers, dyes and other anions and cations to balance the charge in the chemical compounds. In this experiment, we will illustrate a quality control analysis for the determination of phosphorus in plant food by gravimetric analysis. Phosphorus will be determined by precipitation of the insoluble salt magnesium ammonium phosphate hexahydrate according to the reaction: 5H2O(l) + HPO42-(aq) + NH4+(aq) + Mg2+(aq) + OH-(aq) ( MgNH4PO4 . 6H2O(s)
The % P and % P2O5 in the initial sample can be calculated from the mass of MgNH4PO4 . 6H2O obtained using the following method:
mass of MgNH4PO4 .. 6H2O ( moles of MgNH4PO4 .. 6H2O ( moles of P ( mass of P ( %P and mass of MgNH4PO4 .. 6H2O ( moles of MgNH4PO4 .. 6H2O ( moles of P ( moles of P2O5 ( mass of P2O5 ( %P2O5
Prelab Questions
1) Create an organized data table that will include every piece of data for both samples.
2) If a fertilizer says 10-15-10, what does it mean?
3) If a 3.45 g sample of fertilizer is found to form 2.73 g of MgNH4PO4 . 6H2O using the method below, determine the percent of phosphorus, and the percent of P2O5.
Procedure
Prepare 2 samples per group