American Chemical Society Grade Analytical Chemistry Part 8 Summary PDF

Preview

Summary

PRECIPITATION May also be referred to American Chemical Society Grade (ACS) Exceeds most chemicals in purity. 98-99% purity. Mohr pipette Serological pipette Graduated Cylinder Erlenmeyer Flask Beaker Reagent Bottles Uses centrifugal force to separate suspended elements in a solution.  A weighing i...

Description

• • •

May also be referred to American Chemical Society Grade (ACS) Exceeds most chemicals in purity. 98-99% purity.

OTHER TOOLS FOR MEASUREMENT

• • • • • •

Mohr pipette Serological pipette Graduated Cylinder Erlenmeyer Flask Beaker Reagent Bottles

•

Uses centrifugal force to separate suspended elements in a solution.

•

Filters are used to remove suspended particles in a solution by the use of gravity (sometimes assisted by a vacuum)

BALANCES •

 A weighing instrument with the platform enclosed by glass doors in all directions. Sensitive enough that a slight breeze could alter the reading.

INSTRUMENT CARE  A lesser precision instrument than the analytical balance. The platform has no enclosures as the readings usually only includes 1/10th of a gram.  A crude weighing tool that uses counterweights to measure the weight of an analyte.

CALIPER • •

A tool for precisely measuring length or diameter. 2 different sides can be used to measure inner and outer diameter.

VOLUMETRIC GLASSWARE •

Volumetric glasswares are used for precise and accurate measurements as they are typically the instruments with the lowest margin of error.

1. Like all other materials, it is important to read and understand about the different requirements to care for laboratory instruments. 2. For machines, annual calibration is recommended. This should be done by the manufacturer/distributor’s authorized technicians. 3. Pipettes should be washed regularly with mild detergent and water. Take note that some chemicals can etch or damage glasswares, and thus alter the volume that it can contain/transfer. 4. Instruments should not be used irresponsibly. There is no “one-size-fits-all” for these instruments, and so, it is important for you to find out if the instrument/glassware can handle the experiment that you will be doing.

CONTINUATION OF PRECIPITATION METHOD

AUTOMATIC PIPETTES •

• •



Pipettes with a built-in vacuum system that allows for consistent aspiration of a variable or fixed volume. Precision is high. Accuracy is only high if regularly maintained and calibrated. In precipitation gravimetry an insoluble

PRECIPITATION 

Most precipitation gravimetric methods were developed in the nineteenth century compound

forms

when

we

add

a



















precipitating reagent, or precipitant, to a solution that contains our analyte. In most cases the precipitate is the product of a simple metathesis reaction between the analyte and the precipitant; however, any reaction that generates a precipitate potentially can serve as a gravimetric method. after the precipitate has been separated from the solution, it has in some cases to be dried and then weighed; in others, it has to be dried and ignited before weighing. the operations of drying and ignition and the necessary apparatus will now be described.

After separating the precipitate from its supernatant solution, we dry the precipitate to remove residual traces of rinse solution and to remove any volatile impurities. The temperature and method of drying depend on the method of filtration and the precipitate’s desired chemical form. Placing the precipitate in a laboratory oven and heating to a temperature of 110oC is sufficient to remove water and other easily volatilized impurities. Higher temperatures require a muffle furnace, a Bunsen burner, or a Meker burner, and are necessary if we need to decompose the precipitate before its weight is determined. A absorbs moisture, we must remove it before we weigh the precipitate, this is accomplished by folding the filter paper over the precipitate and transferring both the filter paper and the precipitate to a porcelain or platinum crucible. can not withstand high temperatures and are dried in an oven at a temperature below 200oC. gravimetry.

WHAT IS A PRECIPITATION REACTION? In this topic, we will go through an example of finding the





The used in Gooch crucibles can be heated to a maximum temperature of approximately 500oC. Precipitates that are dried (below 250°C) or ignited (above 250°C) should be collected on filter paper, porcelain filtering crucibles or silica filtering crucibles. The temperature at which precipitates are dried or ignited can be determined by a study of thermogravimetry.

THERMOGRAVIMETRY 

is a technique in which a change in the weight of a substance is recorded as a function of temperature or time. It is used in conjunction with other techniques like differential thermal analysis (DTA), gas chromatography and mass spectrometry.



Crystalline precipitates absorb water or solvent can be easily removed by heating the precipitates e. g. cuprous thiocyanate.

WHAT IS PRECIPITATION GRAVIMETRY? 





an analytical technique that uses a precipitation reaction to separate ions from a solution The chemical that is added to cause the precipitation is called the precipitant or precipitating agent. Sometimes you might hear people referring to precipitation gravimetry simply as gravimetric analysis, which is a broader class of analytical techniques that includes precipitation gravimetry and volatilization

amount of an aqueous ionic compound using precipitation ...