A technician needs to determine the concentration of lead ions in a sample of water
a) Suggest a test chemical that can be added to the water sample to preciitate the lead ions. Show a chemical euation for the formation of the precipitate
b) after a precipitate forms, it is filtered and the mass of the dry precipitate is measured. This informationis used to determine the concentrationof lead. Comment on the accuracy of the test. Suggest and explain a potential source of error
Do you know where to start? What do you not understand?
I do not know where to start with this question. How can i find a substance that will form a precipitae with the lead. Could you suggest one and the possible formula
a) One test chemical that can be added to the water sample to precipitate lead ions is sodium sulfide (Na2S). The chemical equation for the formation of lead sulfide (PbS) precipitate is as follows:
Pb2+ (aq) + S2- (aq) → PbS (s)
In this reaction, sodium sulfide reacts with lead ions to form a black insoluble precipitate of lead sulfide.
b) After the formation of the precipitate, filtering and measuring the mass of the dry precipitate can be used to determine the concentration of lead. This method is commonly known as gravimetric analysis.
Regarding the accuracy of this test, gravimetric analysis is generally considered to be a highly accurate method for determining the concentration of a substance. By measuring the mass of the precipitate, one can indirectly determine the amount of lead present in the sample.
However, there can be potential sources of error in this test:
1. Contamination: If the filter paper used for filtration is contaminated or impure, it can introduce additional substances into the precipitate, affecting the accuracy of the results.
2. Loss of Precipitate: During the filtration process, it is possible to lose some of the precipitate. This loss can happen due to imperfect filtration, transfer of the precipitate from the filter paper to the weighing apparatus, or even environmental factors like air currents. These losses can lead to underestimation of the concentration of lead.
3. Incomplete Precipitation: If some lead ions do not completely precipitate as lead sulfide due to low concentrations or incomplete reaction, the mass of the precipitate will be lower than expected, resulting in an underestimation of the lead concentration.
To minimize these errors, it is essential to use high-quality filter paper, ensure thorough and careful filtration, handle the precipitate with caution to prevent loss, and perform the test in controlled conditions to minimize any potential environmental factors. Regular calibration and validation of the equipment used in the analysis can also improve the accuracy of the test.