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gravimetric chapter 26 homework

gravimetric chapter 26 homework - washed with water the...

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Kimberly Hargraves Chem 210 Ch. 26 Homework April 13, 2011 2) The four desirable properties of a gravimetric precipitate are high purity, insolubility, stable composition, and easy filterability. 3) Relative high supersaturation is undesirable in gravimetric precipitation because the supersaturation produces tiny particles or colloids. Gravimetric analysis favors large, easily filtered particles. 4) Measures that are taken to decrease the relative supersaturation during a precipitation are raising the temperature during precipitation, slowly adding and vigorously mixing reagents, maintaining a large sample volume, and using homogenous precipitation. 5) Many ionic precipitates are washed with electrolyte solution instead of pure water because the ionic atmosphere is required to neutralize the surface charge of tiny particles, if the electrolyte is
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Unformatted text preview: washed with water, the charged particles repel each other and the product breaks up or peptization occurs. Peptization results in loss of product through the filter. 6) AgCl will peptize if washed with water so it is washed with HNO 3 instead. Washing the AgCl precipitate helps to remove the droplets of liquid, containing excess liquid. The electrolyte used for washing must be volatile so it will be lost drying. HNO 3 is a volatile electrolyte and it evaporates during drying whereas NaNO 3 is not volatize. 7) Re precipitation improves the purity of the precipitates. During the second precipitation, the concentration of the impurities in the solution is lower than during the first precipitation, and the degree of co-precipitation therefore tends to be lower. For this reason reprecipitation would be employed in gravimetric analysis....
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