Gravimetric Analysis
GRAVIMETRIC ANALYSIS
Methods in GA
Precipitation Method
- involves isolation of an ion in solution by a precipitation reaction, filtering, washing the precipitate free of contaminants, conversion of the precipitate to a product of known composition, and finally weighing the precipitate and determining its mass by difference. From the mass and known composition of the precipitate, the amount of the original ion can be determined.
Volatilization Method
-the analyte or its decomposition products are volatilized at a suitable temperature. The volatile product is then collected and weighed, or alternatively the mass of the product is determined indirectly from the loss in the mass of the sample.
Gravimetric Calculations
Sample Exercise #1:
The piperazine content of an impure commercial material can be determined by precipitating and weighing the diacetate:
(C2H4)2N2H2 + 2 CH3COOH → (C2H4)2N2H2(CH3COOH)2 piperazine piperazine diacetate
In one experiment, 0.3126 gram of the sample was dissolved in 25 mL of acetone, and 1 mL of acetic acid was added. After 5 minutes, the precipitate was filtered, washed with acetone, dried at 110 °C and found to weigh 0.7121 gram. What is the weight percent of piperazine in the commercial material?
Answer: 95.14%
Sample Exercise #2:
To measure the nickel content in steel, the alloy is dissolved in 12 M HCl and neutralized in the presence of citrate ion, which maintains iron in solution. The slightly basic solution is warmed, and dimethylglyoxime (DMG) is added to precipitate the red DMG-nickel complex quantitatively. The product is filtered, washed with cold water and dried at 110 °C.
Ni 2+ + 2 (CH3CNOH)2 → (CH3CNO)4H2Ni + 2 H+ DMG bis-DMG-Nickel complex
If the nickel content is known to be near 3 % by weight and you wish to analyze 1.0 gram of the steel, what volume of 1.0 % by weight alcoholic DMG solution should be used to give a 50% excess of DMG for the analysis? Assume that the
Methods in GA
Precipitation Method
- involves isolation of an ion in solution by a precipitation reaction, filtering, washing the precipitate free of contaminants, conversion of the precipitate to a product of known composition, and finally weighing the precipitate and determining its mass by difference. From the mass and known composition of the precipitate, the amount of the original ion can be determined.
Volatilization Method
-the analyte or its decomposition products are volatilized at a suitable temperature. The volatile product is then collected and weighed, or alternatively the mass of the product is determined indirectly from the loss in the mass of the sample.
Gravimetric Calculations
Sample Exercise #1:
The piperazine content of an impure commercial material can be determined by precipitating and weighing the diacetate:
(C2H4)2N2H2 + 2 CH3COOH → (C2H4)2N2H2(CH3COOH)2 piperazine piperazine diacetate
In one experiment, 0.3126 gram of the sample was dissolved in 25 mL of acetone, and 1 mL of acetic acid was added. After 5 minutes, the precipitate was filtered, washed with acetone, dried at 110 °C and found to weigh 0.7121 gram. What is the weight percent of piperazine in the commercial material?
Answer: 95.14%
Sample Exercise #2:
To measure the nickel content in steel, the alloy is dissolved in 12 M HCl and neutralized in the presence of citrate ion, which maintains iron in solution. The slightly basic solution is warmed, and dimethylglyoxime (DMG) is added to precipitate the red DMG-nickel complex quantitatively. The product is filtered, washed with cold water and dried at 110 °C.
Ni 2+ + 2 (CH3CNOH)2 → (CH3CNO)4H2Ni + 2 H+ DMG bis-DMG-Nickel complex
If the nickel content is known to be near 3 % by weight and you wish to analyze 1.0 gram of the steel, what volume of 1.0 % by weight alcoholic DMG solution should be used to give a 50% excess of DMG for the analysis? Assume that the