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Gravimetric Analysis

Instructions: Answer the following questions, based on your knowledge of gravimetric analysis. Certain questions may require the use of a calculator or of solubility tables.

1.
In gravimetric analysis, which of the following steps has to be carried out after the "drying" of the precipitate?
1. Ignition and incineration
2. Digestion
3. Filtration
4. Washing
2.
In gravimetric analysis, how is the solubility of the precipitate reduced?
1. By adding excess of precipitating reagent
2. By adding minimum precipitating agent
3. By increasing the concentration of analyte
4. By decreasing the concentration of analyte
3.
What is the temperature range for ignition during gravimetric analysis?
1. $250degC - 1200degC$
2. $200 degC - 1000 degC$
3. $150 degC - 500 degC$
4. $100 degC - 350 deg C$
4.
If Q: concentration of the substance momentarily produced in the solution by mixing the reagents
S : equilibrium solubility

then what is the correct representation for "relative supersaturation"?
1. Relative supersaturation = $[Q - S] /S$
2. Relative supersaturation = $[Q + S] / [S]$
3. Relative supersaturation = $[Q xx S] / [S]$
4. Relative supersaturation = $[Q // S] xx S$
5.
At 298 K, the solubility product of silver chloride is $1.1 xx 10^-(1 0)$. What is the solubility of silver chloride in water?
1. $1.05 xx 10^(-5) (mol//L)$
2. $1.03 xx 10^(_6) (mol//L)$
3. $1.10 xx 10^(-7) (mol//L)$
4. $1.02 xx 10^(-5) (mol // L)$
6.
Complete the following reaction, which summarizes the gravimetric estimation of iron:

$Fe^(3+) + 3OH^(-) rarr Fe(OH)_3(s)$
$2Fe(OH)_3(s) rarr$
1. $Fe_2O_3(s) + 3H_2 O$
2. $Fe_3O_4 + 2H_2O$
3. $Fe_2O_3 + 2H_2O$
4. $Fe_3O_4 + 3H_2O$
7.
Which of the following sources of error could account for a higher mass of product than is expected?
1. The precipitate was completed dried, with some loss of product
2. Most of the supposed product is dissolved in aqueous solution
3. The precipitate was not completely dried
4. None of the above
8.
Which of the following statements correctly describes the importance of the dissolved analyte in gravimetric analyses, with regards to its reaction with the solution?
1. It forms a soluble product
2. Its reaction with the solution forms an insoluble product, which can be used to determine the identity of an unknown species
3. It increases the solubility of the solution
4. Reacting with the solution decreases the solubility of the overall system
9.
To help minimize the error in the final determination of the mass of the product in a gravimetric analysis, the insoluble product must be                                             , until the measurement of the mass becomes constant.
10.
Write a net ionic equation for the following scenario in a gravimetric analysis: Lithium Carbonate reacts with Aluminum Chloride.

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