Gravimetric Analysis

Gravimetric Analysis

• Determination of an analyte based on the

_____________
• Simple, but __________ in chemical analysis

• Involves ___________reaction at controlled

condition to _______________________.

mass of a solid

most accurate
precipitation reaction

selectively precipitate species.

Gravimetric Analysis
selectively precipitate
removing?

removing interfering species before measurement

GRAVIMETRIC ANALYSIS
Used to find the % of ________________ in a mixture

• Involves forming a suitable ___________ with the ion in the sample

One particular component

suitable precipitate

Gravimetric Analysis
This procedure is especially suitable for determining of metal ions and anions such as _________.

This procedure is especially suitable for determining of metal ions and anions such as sulphates.

Steps in Gravimetric Analysis

wspdfdwd

weigh the sample

Sample dissolution

Precipitation

Digestion

Filtration & washing of ppt

Drying

Weighing

Data calculation

Steps in Gravimetric Analysis
precipitation

Steps in Gravimetric Analysis

IDEAL— HOW?

• Control parameters to achieve ideal precipitate

• vol os sol’n

• type of precipitate agent

• Presence/concentration of other species in solution that may affect precipitation process

• temp of sol’n

• Ph of sol’n

Gravimetric Analysis
A ______________ amount of some product can be obtained from a ______ like the component of the ______ being assayed by any one of the various methods.

chemically equivalent, , reactant, sample

Gravimetric Analysis
1 may be ________ from solution

2 may be ___________ product resulting from

______ of a compound

3 may be _______ on an _______ by ___________

may be precipitated from solution.
may be decomposition product resulting from

ignition of a compound.

may be deposited on an electrode by electrolysis

Properties of precipitates

• To obtain good results, we must be able to

produce “_______” precipitate that can be

recovered with _______________.

pure, high efficiency

Criteria of Good precipitate

-Have ___ _____

-Be easy to _____ by _______

-Be _______ to air, water.

-Be something where our analyte is only a ______ portion of the ppt.

➢Have low solubility

➢Be easy to recover by filtration

➢Be unreactive to air, water...

➢Be something where our analyte is only a small

portion of the ppt.

The precipitate should:
1. Have a known _______

2. Have a _____ solubility

3. Be stable when ______ (so it does not __________ and can be easily dried

4. Not form ___________ with other _____ that are likely to be present

formula

low solubility

heated, decompose,
precipitates, ions

precipitate form by gravimetric analysis

filtering

vacuum filtering apparatus

Type of suspension and filterability

Colloidal and Crystalline

Type of suspension and filterability

Colloidal
Size range :
Tendency to settle:

Filterability:
Purity:

10-6 – 10-4mm

no
Difficult or impossible
not pure

Type of suspension and filterability

Crystalline

Size range:
Tendency to settle:

Filterability:
Purity:

10-1 – 10 mm
Will settle spontaneously
Readily filtered
Typically higher purity than colloids.

THE FACTORS GOVERN THE PARTICLES

SIZE OF A PRECIPITATE
ptrt

• Precipitate solubility

• Temperature

• Reactant concentration,

• The rate at which reactants are mixed.

The net effect of these variables can be

accounted for, at least qualitatively, by assuming

that the particle size is related to a single

property of the sytem called its

relative supersaturation RSS

The net effect of these variables can be

accounted for, at least qualitatively, by assuming

that the particle size is related to a single

property of the sytem called its

______ __________ ____

relative supersaturation RSS

relative supersaturation where

Q:
S:

Q= conc of the solution everytime

S= equilibrium solubility of the solute

______ can be used to estimate or control the type of precipitate that is formed

RSS

if RSS is large tend to form
if RSS is small tend to form

colloids

crystaline ppt

we can keep crystalline small by

When designing a _____________________ , a knowledge of the __________ of the __________ likely to be produced is important

gravimetric procedure, SOLUBILITIES, precipitates

table the solubility of compoun

Gravimetric Analysis

• Assay of ____________

• Assay of _____ ______ _____ for _________ content

• Assay of _____________________
• Assay of ______________

Sodium chloride

Sodium Lauryl sulfate for Sodium sulfate content

Mercaptomerin Sodium

Sodium phosphate solution

Sodium Lauryl sulfate tx for

surfactant emulsifying agent

Mercaptomerin Sodium tx for

congestive heart failure

Sodium phosphate

laxative to cleans colon before colonoscopy
tx for hypophosphatemid

2 types of method

precipitate and volatilization methods

precipitation method

Based on isolation of an insoluble

precipitate of known composition,

volatization method

–Analyte is volatilized, weighed and the

concentration is determined.

Gravimetric analysis
nitric acid prevent——
helps to——-

• precipitation of ther subs
  insol in water but sol in nitric acid

• coagulate any colloidal silver chloride

Gravimetric analysis
“ The _____ has relationship with the _______

and the _______ _____ or _______ _______”

weight, analyte, material used, actually weight

Gravimetric analysis

Calculations associated with the method are

based on

stoichiometry

stoichiometry definition

quantitative rel. of reactants and products

Stoichiometry of Reaction

• A ________________ gives the ratios, in moles of

materials produced or consumed in a reaction.

balanced formula

Stoichiometry of Reaction
If the _____of anyone species used or produced is __________, the others are ______ calculated.

weight, known, readily

___________________ are simple an extension of

______________________

• Our ___________ _______ is most often based on the amount (in ______) of our analyte in the material actually weighed.

Gravimetric calculations, stoichiometric calculations
stoichiometric factor, moles