Gravimetric Analysis

1. Gravimetric Analysis

2. Design features 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 Weighing the sample Forming a precipitate Filtering the solution Weighing the dry precipitate

3. How it works/ procedure • #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 and discard 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. analysis http://www.youtube.com/watch?v=g6nXgzjW7nw&feature=related • 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.

5. Advantages and disadvantages Advantages • Precise measurement/ high degree of accuracy (6-figure) • Helps in determination of atomic mass, of elements • Doesn’t 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 high concentrations

6. Data interpretation • 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 by the difference between the two.

7. Calibration- pipette • Calibration is predominantly undertaken by gravimetric analysis and is the method most commonly used by laboratories accredited to ISO17025.  There are colorimetric methods in use and these are often used for checking pipettes and for non-accredited calibration. Gravimetric analysis is preferred due to the simplicity and the traceability to an absolute standard. Gravimetric methods are also often recognsied as a more economical way of calibration. • Gravimetric analysis for pipette calibration entails dispensing samples of distilled water into a receiving vessel in a precision analytical balance. The density of water is a known constant, the temperature, barometric pressure and humidity are recorded (the Z-factor used in the final mass calculation) and kept within certain limits and thus the mass of the dispensed sample provides an accurate indication of the volume dispensed.

8. Usefulness and suitability Determining water content of complex materials. Eg. Food and soil Treating ore (part of earth’s layer) Purity evaluation Determination of atomic mass of elements

9. Real world examples • 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 precipitated with Barium and weighed as BaSo4. • Monitoring the air Concentrated HCl to remove nitrate and chlorate BaSO4 Sulfate with nitrate and chlorate

10. comparison • 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. Temp. Volumetric- volume Gravimetric-weight Gravimetric- less sensitive volumetric

11. Volumetric Analysis

12. Design features • 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 Titration/ volumetric analysis Measure from bottom of meniscus

13. How it works/ procedure 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 flask with 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 the end 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=8UiuE7Xx5l8&feature=fvsr

14. Procedurecompleting the titres Equipment

15. Advantages and disadvantages 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. Data interpretation • 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 should all be a similar colour

17. calibration • 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. Suitability/ use and real world examples • 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 acid content. • 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. comparison • 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 to other 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 as gravimetric analysis. Volumetric analysis less accurate