# Gravimetric Analysis

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## Gravimetric Analysis Answer Key

**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?

- Ignition and incineration
- Digestion
- Filtration
- Washing

2.

In gravimetric analysis, how is the solubility of the precipitate reduced?

- By adding excess of precipitating reagent
- By adding minimum precipitating agent
- By increasing the concentration of analyte
- By decreasing the concentration of analyte

3.

What is the temperature range for ignition during gravimetric analysis?

- [math]250degC - 1200degC[/math]
- [math]200 degC - 1000 degC[/math]
- [math]150 degC - 500 degC[/math]
- [math]100 degC - 350 deg C[/math]

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"?

S : equilibrium solubility

then what is the correct representation for "relative supersaturation"?

- Relative supersaturation = [math][Q - S] /S[/math]
- Relative supersaturation = [math][Q + S] / [S][/math]
- Relative supersaturation = [math][Q xx S] / [S][/math]
- Relative supersaturation = [math][Q // S] xx S[/math]

5.

At 298 K, the solubility product of silver chloride is [math]1.1 xx 10^-(1 0)[/math]. What is the solubility of silver chloride in water?

- [math]1.05 xx 10^(-5) (mol//L)[/math]
- [math]1.03 xx 10^(_6) (mol//L)[/math]
- [math]1.10 xx 10^(-7) (mol//L)[/math]
- [math]1.02 xx 10^(-5) (mol // L)[/math]

6.

Complete the following reaction, which summarizes the gravimetric estimation of iron:

[math]Fe^(3+) + 3OH^(-) rarr Fe(OH)_3(s)[/math]

[math]2Fe(OH)_3(s) rarr[/math]

[math]Fe^(3+) + 3OH^(-) rarr Fe(OH)_3(s)[/math]

[math]2Fe(OH)_3(s) rarr[/math]

- [math]Fe_2O_3(s) + 3H_2 O[/math]
- [math]Fe_3O_4 + 2H_2O[/math]
- [math]Fe_2O_3 + 2H_2O[/math]
- [math]Fe_3O_4 + 3H_2O[/math]

7.

Which of the following sources of error could account for a higher mass of product than is expected?

- The precipitate was completed dried, with some loss of product
- Most of the supposed product is dissolved in aqueous solution
- The precipitate was not completely dried
- 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?

- It forms a soluble product
- Its reaction with the solution forms an insoluble product, which can be used to determine the identity of an unknown species
- It increases the solubility of the solution
- 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 dried several times, 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.

- [math]Al^{3+} (aq)+ CO_3^{2-} (aq) rarr Al_2(CO_3)_3 (s)[/math]

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