Gravimetric Analysis and Solubility Product

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Questions and Answers

What term describes the compound that is formed by the reaction of a reagent from a solution in gravimetric analysis?

  • Saturated form
  • Weighed form
  • Soluble form
  • Precipitated form (correct)

What condition indicates that a solution of lead sulphate is supersaturated?

  • [Pb++][SO4--] = 2.2*10-8
  • [Pb++][SO4--] > 2.2*10-8 (correct)
  • [Pb++][SO4--] = 0
  • [Pb++][SO4--] < 2.2*10-8

Which of the following statements correctly explains the effect of using an equivalent amount of precipitant during precipitation?

  • It leads to incomplete precipitation. (correct)
  • It allows for the exact weighing of the precipitate.
  • It has no effect on precipitation completeness.
  • It ensures complete precipitation.

According to the first solubility product rule, what must occur for a precipitate to form?

<p>The concentration of ions must exceed the solubility product. (D)</p> Signup and view all the answers

What is the value of the solubility product (SP) for lead sulfate at 25°C?

<p>2.2*10-8 (C)</p> Signup and view all the answers

To achieve more complete precipitation of Pb++, what must be done with the concentration of SO4-- ions?

<p>It should be increased. (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of desiccators?

<p>Used for precipitate weighing (A)</p> Signup and view all the answers

What consequence follows if the concentration of [Pb++][SO4--] is less than the solubility product?

<p>More PbSO4 can dissolve into the solution. (C)</p> Signup and view all the answers

Which statement describes the relationship between the product of the concentrations of the ions and the solubility product in a concentrated solution?

<p>It is constant at a given temperature and equals the SP. (A)</p> Signup and view all the answers

What must be understood about the different forms in gravimetric analysis?

<p>The two forms represent different aspects of a compound. (D)</p> Signup and view all the answers

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Flashcards

Precipitated form

The compound that is formed when a reagent is added to a solution and causes a solid to precipitate out.

Weighed form

The compound that is weighed at the end of a gravimetric analysis to determine the amount of analyte present.

Solubility Product (SP)

The product of the concentrations of the ions of a sparingly soluble electrolyte in a saturated solution at a given temperature.

Unsaturated solution

A solution where the product of the ion concentrations is less than its SP. More solute can dissolve.

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Saturated Solution

A solution where the product of the ion concentrations is equal to its SP. No more solute can dissolve.

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Supersaturated solution

A solution where the product of the ion concentrations is greater than its SP. Precipitation will occur.

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Excess precipitant

Adding excess of the precipitant to ensure complete precipitation of the analyte.

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2nd Solubility Product Rule

The product of the concentrations of the ions of a sparingly soluble electrolyte in a concentrated solution is always constant at a given temperature, and equals its SP.

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Desiccator

A container used for storing and drying solids by isolating them from external moisture.

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Desiccation

The process of removing moisture from a substance.

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Study Notes

Gravimetric Analysis

  • Distinction between precipitated and weighed forms:
    • Precipitated form: Compound precipitated from solution.
    • Weighed form: Compound weighed to determine final result.

Solubility Product (SP)

  • Saturated solution: Ions' product reaches a constant value (Solubility Product) at a given temperature.
  • Example (PbSO₄ at 25°C): [Pb²⁺][SO₄²⁻] = 2.2 × 10⁻⁸
  • Unsaturated solution: [Pb²⁺][SO₄²⁻] < 2.2 × 10⁻⁸ (more PbSO₄ can dissolve)
  • Supersaturated solution: [Pb²⁺][SO₄²⁻] > 2.2 × 10⁻⁸ (some PbSO₄ must precipitate)
  • Solubility Product Rule 1: Precipitate forms when ion product exceeds SP.

Effect of Excess Precipitant

  • Incomplete precipitation with equivalent amounts.
  • More complete precipitation with excess precipitant .
  • Solubility Product Rule 2: Ion product in concentrated solution equals SP.
  • Higher precipitant concentration reduces ion concentration (to precipitate more completely).

Desiccators

  • Use: Storage and final drying of moisture-sensitive solids.
  • Materials: Plastic, glass, or metal.
  • Function: Maintains dry environment (not drying the material directly).
  • Applications: Electronics, pharmaceuticals, optics, etc.
  • Desiccating agent: Absorbent material (e.g., concentrated sulfuric acid, calcium chloride) - needs replenishing.

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