Gravimetric and Limiting Reagent

Four fundamental types (methods)

1. physical gravimetry
2. Thermogravimetry
3. precipitative gravimetric analysis, and
4. Electrodeposition

Physical gravimetry

is the most common type used in
environmental engineering. It involves the physical separation and classification of matter in environmental samples based on volatility and particle size (e.g., total suspended solids).

Thermogravimetry

samples are heated and changes in sample mass are recorded. Volatile solids analysis is an important example of this type of gravimetric analysis.

Precipitative gravimetry

relies on the chemical precipitation of an analyte.

Electrodeposition

involves the electrochemical reduction of metal ions at a cathode, and simultaneous deposition of the ions on the cathode.

Common Procedures in Gravimetric Analysis

1.Drying to a Constant Weight
2. Drying to a Constant Weight
3. Use of the Analytical Balance

hygroscopic

Reagents that readily pick up water are termed(n)

deliquescent

Those that absorb so much water that they will dissolve in it and
form a concentrated solution are called (n)

0.3 mg

The procedure is repeated until successive weighing agree to
within (n)

Analytical Balance

the most accurate and precise instrument
in an environmental laboratory.

thermogravimetry

Either the change of sample weight is determined

(combustion analysis

the combustion gases are trapped are weighed

Fixed solids

are those that remain as residue after ignition at
550° C for 15 minutes.

volatile solids.

The weight of material lost is called

The two most common gravimetric methods using
volatilization are those for water and carbon dioxide.

1. isolation of sodium hydrogen bicarbonate (the main
ingredient in most antacid tablets) from a mixture of
carbonate and bicarbonate.
2. Determination of water content of a compound by
vaporizing the water using thermal energy (heat).

pure, dry oxygen.

Total carbon and hydrogen can be determined in a solid by
combustion in the presence of

Combustion analysis : Carbon & Hydrogen Analysis

Technique is accurate and usable with a wide range of
compounds.

PRECIPITATIVE GRAVIMETRIC ANALYSIS

requires that the substance to be weighed be readily
removed by filtration.

Mechanism of Precipitation

A supersaturated solution is an unstable solution that
contains more solutes than a saturated solution. With
time, supersaturation is relieved by precipitation
of the excess solute.

Reagent + Analyte → Solid Product (collect
and measure mass)

Principle a

Desired Properties of Solid product

Principle b

Desired Properties of Solid product

Should be very insoluble, Easily filterable, Very Pure, Known and constant composition

10 mg

Macroscopic technique-requires at least ___mg ppt
to collect and weigh properly

ELECTRODEPOSITION

Electrodeposition may be thought of as a special case of
precipitative gravimetry where electrons are the
precipitant. It is generally used for the determination of
metals in concentrated solution. However, it has few, if
any applications in environmental engineering analysis.

500 – 550 deg C

Very dull red heat

550 – 700 deg C

Dull red heat

800 – 1000 deg C

Bright red heat

1000 – 1200 deg C

Yellow red heat

1200-1600 deg C

White heat

Limiting Reagent

-It is defined as a substance /reactant ,that completely get
consumed when the chemical reaction is complete.