Gravimetric Analysis Ppt Chem

5/24/2018 Gravimetric Analysis Ppt Chem

1/19


2/19

Weighing the sample Forming a precipitate Filtering the solution Weighing the dry precipitate

This analytical technique includes: Empirical formula and Molecular formula

Gas equations Eg. Pv=nrt

Percentage of water/ measuring water content

Limiting and Excess reactant equations

Precipitation reactions

Key steps in a

precipitation reaction-

what this looks like


3/19

#1: Accurately weigh the

mixture to be analysed.

#4: Filter off the precipitate

and wash it with a small

quantity of substance.

#2: Dissolve the mixture in a

suitable solvent; filter off anddiscard any insoluble material.

#3: Add an excess amount of

solution, that will form a

precipitate with the substance

being analysed.

#5: Dry the precipitate and,

cool and accurately weigh.Repeat until a constant mass is

achieved.


4/19

Gravimetric analysis is a technique through which the

amount of an analyte (the ion being analyzed) can be

determined through the measurement of mass.

Gravimetric analysis depend on comparing the masses of

two compounds containing the analyte.

http://www.youtube.com/watch?v=g6nXg

zjW7nw&feature=related
http://www.youtube.com/watch?v=g6nXgzjW7nw&feature=relatedhttp://www.youtube.com/watch?v=g6nXgzjW7nw&feature=relatedhttp://www.youtube.com/watch?v=g6nXgzjW7nw&feature=relatedhttp://www.youtube.com/watch?v=g6nXgzjW7nw&feature=related


5/19

Advantages

Precise measurement/

high degree of accuracy

(6-figure)

Helps in determination ofatomic mass, of elements

Doesnt require a series of

standards to calibrate the

unknown solution

concentration Helps in calibration of

other instruments

Disadvantages

Limited group of

elemental analysis

Convoluted methods

Only suitable for highconcentrations


6/19

Gravimetric analytical data is interpreted from the

weighing of the precipitate at the end of the experiment.

To do this, you must weigh the instrument in which the

precipitate will be weighed in, note the weight, and then

weigh the precipitate. The solid weight is determined bythe difference between the two.


7/19

Calibration is predominantly undertaken by gravimetricanalysis and is the method most commonly used bylaboratories accredited to ISO17025. There are colorimetricmethods in use and these are often used for checking pipettesand for non-accredited calibration. Gravimetric analysis ispreferred due to the simplicity and the traceability to an

absolute standard. Gravimetric methods are also oftenrecognsied as a more economical way of calibration.

Gravimetric analysis for pipette calibration entails dispensingsamples of distilled water into a receiving vessel in aprecision analytical balance. The density of water is a known

constant, the temperature, barometric pressure and humidityare recorded (the Z-factor used in the final mass calculation)and kept within certain limits and thus the mass of thedispensed sample provides an accurate indication of thevolume dispensed.


8/19

Determination of atomic

mass of elements

Purity evaluation

Determining water content of

complex materials. Eg. Food

and soil

Treating ore (part

of earths layer)


9/19

Geomarine survey systems

A chunk of ore is treated with concentrated nitric acid and

potassium chlorate to convert all of the sulfur to sulfate.

The nitrate and chlorate are removed by treating the

solution with concentrated HCl. The sulfate is precipitatedwith Barium and weighed as BaSo4.

Monitoring the air

Sulfate with

nitrate and

chlorate

Concentrated HCl to

remove nitrate and

chlorate BaSO4


10/19

Gravimetric analysis obtains more accurate data about the

composition of a sample than volumetric analysis does,

however it takes longer to perform in the laboratory.

Gravimetric analysis is analysis by weight, where as

volumetric analysis is by volume. Gravimetric analysis is less sensitive to temperature than

volumetric analysis is.

volumetricGravimetric-less sensitive

Temp.

Gravimetric-weight

Volumetric- volume


11/19


12/19

Looks like a titration/ same as

Measure from bottom of meniscus

Wherever there is a concentration of a known solution, to

be found, then volumetric analysis is the method to use.

Quantative analytical technique

Measure from bottom

of meniscus

Titration/

volumetric

analysis


13/19

Steps

Clean the pipette and rinse it with a

bit of the solution to be used.

Clean a conical flask using distilled

water.

Pipette the specified volume of one

reactant into the flask.

Rinse down the edges of the flaskwith distilled water.

Add the indicator if required.

Clean the burette and rinse with bit

of the second reactant solution. Fill

with the solution. Does not need to

be exactly on zero. Note the reading

on the bottom of the meniscus.

Perform a preliminary (rough)

titration by running the burette

solution into the flask, making sure to

swirl the mix, until the end point is

reached.

Read the meniscus again. Subtract the

first reading to find the volume

added.

Repeat the first 5 steps.

Read the burette and perform an

accurate titration by repeating step

7.

Stop as soon as the end point is

reached.

Subtract the initial reading from theend point reading to give an accurate

titre.

Repeat the accurate titration (steps

9-12) at least twice more. The titres

should be within 0.1cm of each other.

Take an average of your three

accurate titres. Use this as the

volume added in the calculations.

http://www.youtube.com/watch?v=8UiuE

7Xx5l8&feature=fvsr
http://www.youtube.com/watch?v=8UiuE7Xx5l8&feature=fvsrhttp://www.youtube.com/watch?v=8UiuE7Xx5l8&feature=fvsrhttp://www.youtube.com/watch?v=8UiuE7Xx5l8&feature=fvsrhttp://www.youtube.com/watch?v=8UiuE7Xx5l8&feature=fvsr


14/19

Equipment


15/19

Advantages

Fast and easy to perform

Only basic laboratory

equipment needed

Very cheap Accurate results

Different methods

available for different

substances

Disadvantages

Relatively large sample

size needed

Only suitable for relatively

high concentrations


16/19

Data is interpreted by using three concordant titres. These

help to give accurate results and need to be within 0.1 of

each other.

Concordant titres- they shouldall be a similar colour


17/19

To ensure proper measurement of

large volumes in the laboratory,

volumetric apparatus should be

calibrated regularly. Two of the most

common apparatus calibrated are

volumetric flasks and serological

pipettes.

*If the error is more than 0.03% then

the apparatus should be discarded or

changed into a volumetric apparatus

Manual procedure via volumetric flask

- Weigh the volumetric flask.

- Fill the volumetric flask with distilled

water, up to the mark

- Weigh the volume of distilled water

contained in the flask.

- Calculate the true volume of

glassware via the formula

- Record the data

- Do the same procedure with the

serological pipette.

- Record again your data.


18/19

Used in bio diesel manufacture to ensure that the mix has

a neutral pH.

To determine the amount of acetic acid in manufactured

vinegar.

To determine fatty-acid content and unsaturated-fatty acidcontent.

Brain imaging and MR imaging, as well as routine clinical

use.

Suitable for direct titrations

Suitable in Determination of iron

Manufactured

vinegar

brain imaging


19/19

Compared to other analysis; for example gravimetric

analysis, volumetric analysis is less accurate and less

reliable.

In volumetric analysis, you are more likely to encounter

limits of sensitivity in volume measurements, compared toother analytical techniques.

A mass is generally easier to determine and standardize

than a concentration.

Errors associated with volume measurements are

minimized in other analytical techniques, such asgravimetric analysis.

Volumetric analysis less accurate

Gravimetric Analysis Ppt Chem

Documents

Transcript of Gravimetric Analysis Ppt Chem