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Flashcards in Heterogeneous Solutions Deck (25)
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1
Q

Gravimetric analysis

A
  1. ) preparation of analyte solution
  2. ) precipitation
  3. ) digestion of the precipitate
  4. ) filtration and washing of the precipitate
  5. ) drying and weighing of the precipitate
  6. ) determination of amount of analyte present
2
Q

Properties of precipitates and precipitants

A

Specificity and Selectivity- should be specific and react with only one chemical species

3
Q

Important points of gravimetric analysis

A

Ease of recovery of analyte, particle size, colloidal and crystalline suspensions, factors determining particle size

4
Q

Factors determining particle size

A

Precipitate solubility (S) & solute concentration (Q) determine particle size which is related to a property for he system called relative supersaturation

5
Q

Relative supersaturation (rs)

A

Q-S/S = relative supersaturation

When rs is large = colloidal
When rs is small = crystalline

6
Q

Experimental conditions

A

Should be chosen to minimize Q and maximize S

7
Q

Mechanism of precipitate formation

A

Nucleatuon & particle growth

8
Q

Nucleation

A

A small number of particles join together to produce a small solid, which may then grow further

9
Q

Solubility

A

Defined as the number of grams of solute necessary to form a saturated solution in one kilogram of water

10
Q

Fundamental rule of solubility

A

Like dissolves like

11
Q

Heat of dissociation

A

The change in enthalpy that accompanies the formation of a solution

12
Q

Factors influencing dissolution

A
  1. ) structure
  2. ) pressure
  3. ) temperature
13
Q

Structure

A

Solubility increases if both solute and solvent have similar polarities

14
Q

Pressure

A

Pressure exerts a remarkable effect on only gasses, the influence of pressure on solubility of gases is best expressed by Henry’s Law

15
Q

Henry’s Law

A

In the absence of chemical reaction between the solute and the solvent, the quantity of gases dissolved in a solution is directly proportional to the pressure of the gas above the solution

16
Q

Temperature

A

Dissolution of solids occurs more rapidly at higher temps

The solubility of gas and liquid decrease with temperature

17
Q

Solubility product constant (Ksp)

A

Equilibrium expression for equilibrium that exists between the solute and its ions in a saturated solution of slightly soluble ionic compound

18
Q

Solubility product constant for PbI2

A

Ksp = [Pb^2+][I^-]^2

The equilibrium is independent of the amount of undissolved solute present

19
Q

Precipitation titrations

C- analyte with the concentration Mc-, with AgNO3

A

Preequivalence points
Equivalence point
Postequivalence points

20
Q

Preequivalence points

Ag+ + C- -> AgC, Ksp = [Ag+][C-]

A

Up to equivalence point, C- will be present in excess. Two steps are required to calculate the preequivalence point concentration of [C-].

21
Q

Preequivalence points

Ag+ + C- -> AgC, Ksp = [Ag+][C-]

A

[C-] = ((Vc•Mc)-(Vag•Mag)/Vc + Vag) + Ksp/[C-]

22
Q

Correction factor

A

= [C-] = [Ag+] = Ksp/ ([Ag]/[C-])

Not needed if solution is very dilute or very near equivalence point

23
Q

Equivalence point

A

[Ag+] = [C-] = (Ksp)^1/2

24
Q

Post equivalence point

A

[Ag+] = (((VAg•MAg)-(Va-•Mac-))/ Vc- + Vag) + Ksp/[Ag]

25
Q

Complexing agents

A

EDTA